JP2015048500A - Metal material and method of producing metal material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal material which can keep ductility while increased in strength.SOLUTION: The metal structure of a metal material contains a fine grain structure region 1 composed of fine crystal grains 1a and a plurality of coarse grain structure regions 2 composed of coarse crystal grains 2a having an average crystal grain size larger than the average crystal grain size of the fine crystal grains 1a. The fine grain structure region 1 has a network structure with the plurality of coarse grain structure regions 2 dispersed and dotted in the fine grain structure region 1. The fine crystal grains 1a form a two-phase structure containing two types of crystal grains mutually different in crystal structure.

Description

  The present invention relates to a metal material obtained by sintering metal powder particles, and a method for producing the metal material.

Generally, in order to increase the strength of a metal material, the crystal structure may be refined.
For example, in Patent Document 1, regarding the refinement of the crystal structure of a Co—Cr—Mo alloy used as a biomaterial, nitrogen is added to the alloy in advance to precipitate fine nitrides in the structure. A method is disclosed. According to this method, the precipitation strengthening by nitride can be achieved while the crystal structure is refined by suppressing the growth of crystal grains by the fine nitride deposited in the structure.

Japanese Unexamined Patent Publication No. 2011-184783

  However, in the above-described conventional example, it is possible to increase the strength as a metal material by refining the crystal structure, but the higher the strength, the lower the ductility, not only lower the workability, There is a possibility that the suitability as a metal material for a living body may be impaired.

  This invention is made | formed in view of such a situation, and it aims at providing the technique for obtaining the metal material which can maintain a ductility, raising a intensity | strength.

The inventors of the present application have made extensive studies on metal materials that can maintain ductility even when the strength is increased. Among them, the knowledge that the ductility can be maintained even if the strength is increased by combining the fine crystal structure necessary for increasing the strength and the coarse crystal structure necessary for maintaining the ductility, with an appropriate structure. Got.
The present inventors have completed the present invention based on the above findings.

(1) That is, the present invention is a metal material substantially composed of a single metal or alloy, and the metal structure of the metal material is a fine grain structure region constituted by fine crystal grains; A plurality of coarse grain structure regions composed of coarse crystal grains having an average crystal grain size larger than an average crystal grain size of the crystal grains, and the fine grain structure region includes the plurality of coarse grain structure regions. By being dispersed in the fine grain structure region, a network structure is formed, and the fine crystal grains have a two-phase structure by including two kinds of crystal grains having different crystal structures.

According to the metal material configured as described above, a plurality of coarse grain structure regions are dispersed and dispersed in the fine grain structure region, whereby the fine grain structure region contributing to high strength of the metal material has a mesh shape. Since it is made into an organization, the strength of the entire material can be increased while maintaining the degree of freedom of deformation. Furthermore, since a coarse grain structure region that contributes to maintaining the ductility of the metal material is arranged inside the mesh of the fine grain structure area, strength is borne by the fine grain structure area, and ductility is borne by the coarse grain structure area. Can be made. As a result, ductility can be maintained while increasing strength.
Further, since the fine grain structure region has a two-phase structure by including two kinds of crystal grains having different crystal structures, the degree of freedom in adjusting strength and ductility by combining different crystal grains. Can be increased.

(2) In the metal material, the crystal structure of one of the two types of crystal grains is preferably a hexagonal close-packed structure. In this case, crystal grains having a hexagonal close-packed structure advantageous in terms of strength are other than the hexagonal close-packed structure. Compared to the case of a single-phase structure of only a hexagonal close-packed crystal grain or a crystal grain other than a hexagonal close-packed structure, for example, it is appropriately dispersed to such an extent that the ductility is not impaired. The strength of the fine grain structure region can be increased. As a result, the strength of the metal material can be further increased while maintaining ductility.

(3) In addition, when the crystal grains having a hexagonal close-packed structure have a ratio of less than 40% with respect to the cross-sectional area ratio of the fine grain structure region, the fine grain structure region may not be able to obtain the required strength. There is.
For this reason, it is preferable that the crystal grain whose crystal structure is a hexagonal close-packed structure is contained at a ratio of 40% or more with respect to the cross-sectional area ratio of the fine grain structure region. By comprising in this way, required intensity | strength can be provided to a fine grain structure area | region.

(4) Moreover, it is preferable that the ratio of the said fine grain structure area | region is 20% or more and 70% or less in a cross-sectional area ratio. When the ratio of the fine grain structure region is less than 20% in terms of the cross-sectional area ratio, the strength of the metal material may not be sufficiently increased. Further, if the ratio of the fine grain structure region is larger than 70% in terms of the cross-sectional area ratio, the required ductility may not be ensured.

(5) Moreover, it is preferable that the average crystal grain diameter of the said fine crystal grain is 5 micrometers or less. This is because if the average crystal grain size of the fine crystal grains is larger than 5 μm, the fine grain structure region may not obtain the required strength.

(6) It is preferable that the metal material is formed by sintering powder particles made of the substantially single metal or alloy. In this case, the crystal structure of the metal material can be easily controlled by adjusting the crystal structure of the powder particles.

(7) The single metal or alloy is preferably at least one selected from a Co—Cr—Mo alloy, an austenitic stainless steel, and a manganese steel.

(8) Moreover, this invention is a manufacturing method of the metal material obtained by sintering the powder particle which consists of the said substantially single metal or an alloy, (A) On the surface of the said powder particle, The surface portion fine grain structure region formed by the fine crystal grains having an average crystal grain size smaller than the average crystal grain size of the crystal grains constituting the powder particles is formed on the surface. And (B) said intermediate | middle which has a coarse-grain structure area | region comprised by the coarse crystal grain of an average crystal grain size larger than the average crystal grain size of said fine crystal grain in the center part, By sintering the particles, the surface fine-grain structure regions of each intermediate particle are bonded to each other, and the metal structure is a fine structure having a network structure by bonding the surface fine-grain structure regions to each other. Grain structure region and the middle A metal material including a plurality of the coarse grain structure regions included in the child, wherein the plurality of coarse grain structure regions are disposed inside the mesh of the fine grain structure region. And the step (B) is different from the solid phase of the fine crystal grains constituting the fine grain structure region before the temperature rise due to the temperature rise when the intermediate particles are sintered in the step (B). The solid phase crystal grains are precipitated in the metal structure.

  According to the method for producing a metal material having the above-described configuration, the solid phase crystal grains different from the solid phase of the fine crystal grains constituting the fine grain structure region before the temperature rise due to the temperature rise in the step (B). Therefore, the fine grain structure region can be made a metal structure composed of finer crystal grains. As a result, even if it is kept at a higher temperature thereafter, it is possible to suppress the coarsening of the fine crystal grains constituting the fine grain structure region.

(9) (10) In the step (A), it is preferable to form the surface portion fine grain structure region on the surface of the powder particles by subjecting the powder particles to strong processing. The mechanical milling process is preferred.
In this case, the surface part fine grain structure area | region which has a fine grain structure can be formed in the intermediate particle surface by performing the strong process by the mechanical milling process on the surface of a powder particle.

(11) In the step (A), the portion of the metastable phase present on the surface of the powder particles is transformed into a stable phase by the mechanical milling treatment, so that the surface of the powder particles is substantially stabilized. In the step (B), the other solid phase is a metastable phase, and the intermediate particles are heated by sintering when the intermediate particles are sintered. It is preferable to precipitate metastable phase crystal grains in the fine grain structure region.

  In this case, even if the powder particles include a metastable phase, the surface portion fine grain structure region can be substantially made into a single phase of the stable phase by the step (A). It can be made into a substantially stable single phase. For this reason, by the temperature increase in the step (B), the crystal grains of the metastable phase can be surely and uniformly precipitated, and the fine grain structure region can be uniformly refined. As a result, the coarsening of crystal grains in the fine grain structure region can be suppressed uniformly.

(12) Also, in the step (B), by raising the temperature so that the single metal or alloy passes the temperature at which solid phase transformation starts, the other solid phase crystal grains are precipitated. Is preferred.

(13) In the above method, the single metal or alloy is at least one selected from a Co—Cr—Mo alloy, an austenitic stainless steel, a Ti—Al—V alloy, a Ni—Ti alloy, and a manganese steel. It is preferable that

  According to the present invention, it is possible to obtain a metal material capable of maintaining ductility while increasing strength.

It is the figure which showed typically the metal structure of the metal material which concerns on one Embodiment of this invention. It is a figure which shows the manufacturing method of the metal material which concerns on this embodiment. It is sectional drawing which showed typically the aspect of the crystal grain of the powder particle which changes with each process at the time of manufacturing a metal material. It is a figure which shows an example of the sintering conditions in a sintering process. It is the figure which showed the change of the crystal grain of the fine-grain structure area | region of the metal material in a sintering process, (a) is the figure which showed the relationship between the temperature conditions in a sintering process, and the temperature which starts a transformation, (b) is a figure which shows the change of the crystal grain of the fine grain structure area | region in the temperature area | region of each phase. It is a figure which shows the other example which showed the change of the crystal grain of the fine-grain structure area | region 1 of the metal material in a sintering process, (a) is the temperature conditions in the sintering process of this example, and the temperature which starts a transformation (B) is a figure which shows the change of the crystal grain of the fine grain structure area | region in the temperature area | region for every phase in this example. It is a figure which shows the observation result of the intermediate particle in Test Example 1, (a) is the observation result of the intermediate particle obtained in Experimental Example 1, (b) is the observation result of the intermediate particle obtained in Experimental Example 2. (C) is an observation result of the intermediate particles obtained in Experimental Example 3, and (d) is an observation result of the intermediate particles obtained in Experimental Example 4. It is a figure which shows the X-ray-diffraction pattern of the intermediate particle by Experiment 2, the figure which shows the thing (processing time 0ks: Experimental example 1) which the lowermost stage has not performed the mechanical milling process, and the uppermost stage performed the mechanical milling process It is a figure which shows the latter thing (processing time 54ks: Experimental example 2). The second and third stages from the bottom show X-ray diffraction patterns with mechanical milling time of 0.6 ks and 3.6 ks. It is a figure which shows the X-ray-diffraction pattern of the intermediate particle by Test Example 2, and has shown the X-ray-diffraction pattern by Experimental Examples 1-4. It is a figure which shows the temperature condition and pressure condition in Experimental example 5. FIG. It is a figure which shows the crystal grain boundary map in each metal material in Test Example 3, (a) is the crystal grain boundary map of the metal material obtained in Experimental Example 5, and (b) is obtained in Experimental Example 6. The crystal grain boundary map of the metal material, (c) is the crystal grain boundary map of the metal material obtained in Experimental Example 7, and (d) is the crystal grain boundary map of the metal material obtained in Experimental Example 8. (A) is a graph which shows the relationship between the cross-sectional area ratio of a fine grain structure area | region, and the processing time of a mechanical milling process, (b) is a crystal grain which comprises a fine grain structure area | region and a coarse grain structure area | region. It is a graph which shows the relationship between an average crystal grain diameter and the processing time of a mechanical milling process. It is a Co-Cr binary state diagram. It is a figure for demonstrating the measurement location in a micro Vickers hardness test. It is a figure which shows the measurement result of the cross-sectional hardness of each metal material by Test Example 5, and is a figure which shows the average value of each cross-section hardness measurement value of Experimental Examples 5-8, and the width | variety of the value. 10 is a frequency distribution graph regarding the measurement results of the cross-sectional hardness of each of Experimental Examples 5 to 8 according to Test Example 5. 10 is a stress-strain curve obtained by a tensile test according to Test Example 6. It is a figure which shows the relationship between the tensile strength obtained by the tension test, and elongation at break. It is a figure which shows the X-ray-diffraction pattern by Test Example 7, and has shown the X-ray-diffraction pattern of the test piece before the tension test in each of Experimental Examples 5-8. It is a figure which shows the X-ray-diffraction pattern by Test Example 7, and has shown the X-ray-diffraction pattern of the test piece after the tension test in each of Experimental Examples 5-8. It is a figure which shows the observation result of the intermediate particle by Test Example 8, (a) is the observation result of the intermediate particle obtained in Experimental Example 9, (b) is the observation result of the intermediate particle obtained in Experimental Example 10. It is. It is a figure which shows the cross-sectional observation result of the intermediate particle by Test Example 9, (a) is the observation result of the whole cross section of the intermediate particle obtained in Experimental Example 9, (b) is an expansion of the surface part of (a). The observation result, (c) is the observation result of the entire cross section of the intermediate particle obtained in Experimental Example 10, and (d) is the enlarged observation result of the surface portion of (c). It is a figure which shows the temperature condition and pressure condition by Experimental example 12. It is a figure which shows the crystal grain boundary map in each metal material by Test Example 10, (a) is the crystal grain boundary map of the metal material obtained in Experimental Example 12, and (b) is obtained in Experimental Example 13. The crystal grain boundary map of the metal material, (c) is the crystal grain boundary map of the metal material obtained in Experimental Example 14. (A) is a graph which shows the relationship between the cross-sectional area ratio of a fine grain structure area | region, and the processing time of a mechanical milling process, (b) is the average crystal | crystallization of the crystal grain which comprises a fine grain structure area | region and a coarse grain structure area | region. It is a graph which shows the relationship between a particle size and the processing time of a mechanical milling process. It is a figure which shows the relationship between the tensile strength obtained by the tensile test by Test Example 12, and breaking elongation. It is a figure which shows the observation result of the intermediate particle by Test Example 13, (a) is the observation result of the intermediate particle obtained in Experimental Example 15, (b) is the observation result of the intermediate particle obtained in Experimental Example 16. It is. It is a figure which shows the cross-sectional observation result of the intermediate particle by Test Example 14, (a) is the observation result of the whole cross section of the intermediate particle obtained in Experimental Example 15, (b) is the intermediate obtained in Experimental Example 16. An observation result of the entire cross section of the particle, (c) is an enlarged observation result of the surface portion of (b). It is a figure which shows the temperature condition and pressure condition by Experimental example 17. It is a figure which shows the crystal grain boundary map in each metal material by Test Example 15, (a) is the crystal grain boundary map of the metal material obtained in Experimental Example 17, and (b) is obtained in Experimental Example 18. It is a crystal grain boundary map of a metal material. It is a figure which shows the relationship between the tensile strength obtained by the tensile test by Test Example 16, and breaking elongation. It is a figure which shows the observation result by Test example 17, (a) is a crystal grain boundary map of the metal material obtained in Experimental example 6, (b) is a figure which shows the phase distribution of the same part as (a). is there. It is a figure which shows the X-ray-diffraction pattern by Experiment 18, and shows the X-ray-diffraction pattern of Experimental Example 19 in the upper stage, and the X-ray-diffraction pattern of Experimental Example 6 in the lower stage. 20 is a stress-strain curve obtained by a tensile test according to Test Example 19.

[Composition of metal material]
Hereinafter, preferred embodiments will be described with reference to the drawings.
FIG. 1 is a diagram schematically showing a metal structure of a metal material according to an embodiment of the present invention. In FIG. 1, the crystal grain boundaries of the metal material are exaggerated.

  This metal material is formed using a substantially single metal or alloy as a raw material. Examples of the raw material used for the metal material include a Co—Cr—Mo alloy, an austenitic stainless steel, and a manganese steel.

  As shown in FIG. 1, the metal structure of the metal material of the present embodiment has a fine grain structure region 1 composed of fine crystal grains 1a and an average crystal grain size larger than the average crystal grain diameter of the fine crystal grains 1a. And a plurality of coarse grain structure regions 2 constituted by the coarse crystal grains 2a.

The metal structure of the metal material has a plurality of coarse grain structure regions 2 dispersed in the fine grain structure region 1 with the fine grain structure region 1 as a matrix. The plurality of coarse grain structure regions 2 are scattered in the fine grain structure region 1 three-dimensionally. Therefore, the fine grain structure region 1 has a three-dimensional network structure.
That is, the metal material of the present embodiment is a metal composed of a fine grain structure region 1 (shell) having a network structure and a coarse grain structure region 2 (core) disposed inside the network of the fine grain structure region 1. It is composed of an organization (harmonious organization).

  Further, the fine crystal grains 1a constituting the fine grain structure region 1 include two types of crystal grains (first crystal grains 1a1 and second crystal grains 1a2) having different crystal structures. That is, the fine grain structure region 1 has a two-phase structure including the first crystal grain 1a1 and the second crystal grain 1a2.

  As described above, in the present metal material, since the fine grain structure region 1 that contributes to increasing the strength of the metal material is a network structure, the strength of the entire metal material is increased while maintaining the degree of freedom of deformation. be able to. Furthermore, since the coarse grain structure region 2 that contributes to maintaining the ductility of the metal material is disposed inside the mesh of the fine grain structure region 1, the fine grain structure region 1 is borne for strength, and the coarse grain is obtained for ductility. The tissue area 2 can be burdened. As a result, a metal material that can maintain ductility while increasing strength can be obtained.

  In addition, since the fine grain structure region 1 has a two-phase structure including the first crystal grain 1a1 and the second crystal grain 1a2, it is possible to freely adjust the strength and ductility by combining different crystal grains. The degree can be increased.

  For example, it is preferable that the crystal structure of one of the first crystal grain 1a1 and the second crystal grain 1a2 is a hexagonal close-packed structure. The crystal grains of the hexagonal close-packed structure are more advantageous in strength than the crystal grains of other structures. Such strength-advantageous hexagonal close-packed crystal grains can be appropriately dispersed in crystal grains other than the hexagonal close-packed structure, for example, only hexagonal close-packed crystal grains, or crystal grains other than the hexagonal close-packed structure Compared with the case of this single phase structure, the strength of the fine grain structure region can be appropriately increased to such an extent that the ductility is not impaired. As a result, the strength of the metal material can be further increased while maintaining ductility.

Moreover, when the crystal grain 1a whose crystal structure is a hexagonal close-packed structure is a ratio of less than 40% with respect to the cross-sectional area ratio of a fine grain structure area | region, there exists a possibility that the fine grain structure area | region 1 cannot obtain required intensity | strength. is there.
For this reason, it is preferable that the crystal grain whose crystal structure is a hexagonal close-packed structure is contained at a ratio of 40% or more with respect to the cross-sectional area ratio of the fine grain structure region. By comprising in this way, required intensity | strength can be provided to a fine grain structure area | region.

Moreover, it is preferable that the ratio of the fine grain structure area | region 1 is 20% or more and 70% or less in a cross-sectional area ratio. When the ratio of the fine grain structure region 1 is less than 20% in terms of the cross-sectional area ratio, the strength of the metal material may not be sufficiently increased. Furthermore, the ratio of the fine grain structure region 1 is more preferably 40% or more in terms of the cross-sectional area ratio. In this case, the strength can be sufficiently increased.
Therefore, the crystal grains having a hexagonal close-packed structure may be included at least 8% or more in terms of the cross-sectional area ratio, and more preferably 16% or more.
Further, if the ratio of the fine grain structure region 1 is larger than 70% in terms of the cross-sectional area ratio, the strength can be increased, but the required ductility may not be ensured.

  The average crystal grain size of the fine crystal grains 1a is preferably 5 μm or less. This is because if the average crystal grain size of the fine crystal grains 1a is larger than 5 μm, the fine grain structure region 1 may not be able to obtain the required strength.

  In the present specification, “average crystal grain size” means processing image data of a cross-sectional structure or grain boundary map of a metal material by a scanning electron microscope (SEM) using image analysis software, It refers to a value obtained by calculating the area of the target crystal grains, averaging the diameter of a circle having the same area as the determined area as the particle diameter, and calculating the particle diameter of a predetermined number of samples.

  The “cross-sectional area ratio” is the ratio of the target tissue region in the cross section of the metal material. For example, the cross-sectional area ratio of the fine grain structure region 1 is an observation of an arbitrary cross section of the metal material. It can be obtained by measuring the area of the fine grain structure region 1 in one visual field when it is performed and calculating the ratio (%) to the area of the observation visual field.

  The “average crystal grain size” and “cross-sectional area ratio” were determined using analysis software (trade name: EBSD analysis software AZtecHKL, manufactured by Oxford Instruments Co., Ltd.).

The metal material can be formed by sintering powder particles made of the single metal or alloy described above. In this case, the crystal structure of the metal material can be easily controlled by adjusting the crystal structure of the powder particles.
Hereinafter, the manufacturing method of a metal material is demonstrated.

[Production method of metal material]
FIG. 2 is a diagram illustrating a method for manufacturing a metal material according to the present embodiment. Moreover, FIG. 3 is sectional drawing which showed typically the aspect of the crystal grain of the powder particle 3 which changes with each process at the time of manufacturing a metal material.

In order to manufacture the metal material, as shown in FIG. 2, first, powder particles 3 made of the above-mentioned raw material (single metal or alloy) and balls 4 are respectively prepared in predetermined amounts, and a ball mill device 5 is prepared. The powder particles 3 are subjected to mechanical milling (Mechanical Milling: hereinafter also referred to as MM treatment) as a strong processing to obtain intermediate particles 6 (see FIG. 3B) (see FIG. 3B). Mechanical milling process).
The mechanical milling process is a process capable of performing strong processing by continuously applying a shock to the powder to be treated by continuously rotating a container in which the powder to be treated is charged together with a metal ball or the like.
According to this mechanical milling process, the entire surface of the powder to be processed can be uniformly strongly processed.

The powder particles 3 before the mechanical milling treatment are composed of relatively coarse crystal grains 7 as shown in FIG.
In the present embodiment, the powder particles 3 are strongly processed by mechanical milling. As a result, as shown in FIG. 3 (b), the surface portion fine grain structure region 8 composed of the surface portion fine crystal grains 8 a which are fine crystal grains can be formed on the surface of the powder particle 3.
The surface portion fine grain structure region 8 formed by the mechanical milling process is uniformly formed on the entire surface of the powder particle 3.

The mechanical milling process refines only the crystal grains 7 in the vicinity of the surface without affecting the crystal grains 7 present at the center of the powder particles 3.
Therefore, the intermediate particles 6 obtained by the mechanical milling process have the coarse crystal grains 2a having the surface fine grain structure region 8 on the surface and coarser crystal grains 7 than the surface fine crystal grains 8a in the center. It has a coarse grain structure region 2 configured.

The powder particles 3 to be mechanically milled are powders produced by a rotating electrode method or an atomizing method, and the average particle size varies depending on the type of raw material, the production method, etc. In order to affect the cross-sectional area ratio of the coarse grain structure region 2 after being processed, it is necessary to set appropriately.
When the average particle diameter of the powder particles 3 is relatively small, the area of the coarse grain structure region 2 generated in the center of the powder particle 3 when the surface part fine grain structure region 8 is formed by mechanical milling processing is the surface portion. There is a concern that the fine grain structure region 8 may be significantly reduced. For this reason, the average particle diameter of the powder particles 3 is preferably set to 100 μm or more, more preferably 200 μm or more. Moreover, when the average particle diameter of the powder particles 3 is relatively large, when the surface fine grain structure region 8 is formed by mechanical milling, the area of the coarse grain structure region 2 generated in the center of the powder particle 3 is There is a concern that the surface portion fine grain structure region 8 may become significantly large. For this reason, the average particle diameter of the powder particles 3 is preferably set to 400 μm or less, more preferably 300 μm or less.

  The average crystal grain size of the powder particles 3 affects the crystal grain size of the surface portion fine crystal grains 8a obtained by the mechanical milling process and the coarse crystal grains 2a of the coarse grain structure region 2, and therefore needs to be set appropriately. is there. For example, when the average crystal grain size of the surface fine crystal grains 8a obtained by the mechanical milling process is 5 μm or less, the average crystal grain size of the powder particles 3 needs to be set larger than 5 μm. As described later, the surface portion fine grain structure region 8 and the coarse grain structure region 2 of the intermediate particle 6 constitute a fine grain structure region 1 and a coarse grain structure region 2 included in the metal material by sintering. Become. Therefore, the coarse grain structure region 2 affects the ductility when a metal material is used. Therefore, the average crystal grain size of the powder particles 3 is preferably set to 10 μm or more, more preferably 30 μm or more, from the viewpoint of ensuring the ductility of the metal material.

In addition, when a Co—Cr—Mo alloy or an austenitic stainless steel is used as a raw material, for example, an alloy powder manufactured by a rotating electrode method, an atomizing method, or the like is rapidly solidified, so that it is substantially May be a metastable single phase. That is, the crystal grains 7 of the powder particles 3 before the mechanical milling process may contain a lot of metastable phases.
Furthermore, when a Co—Cr—Mo alloy or austenitic stainless steel is processed from a metastable phase, the processed portion is transformed into a work-induced martensite and work hardening occurs.
For this reason, when the crystal grain structure of the powder particle 3 before the start of the mechanical milling process includes a metastable phase part, the metastable phase part existing on the surface of the powder particle 3 is a stable phase by the mechanical milling process. By transforming into martensite, the surface portion fine grain structure region 8 which is substantially a single phase of a stable phase can be formed on the surface of the intermediate particle 6.

  Returning to FIG. 2, the balls 4 put into the container 5 a together with the powder particles 3 can be subjected to strong processing on the surface of the powder particles 3, and can suppress the mixing of impurities derived from the balls 4. A ball made of a material that can be used is desirable. For example, a ball made of the same material as the powder particles 3, cemented carbide, bearing steel, chrome steel, ceramics, or the like can be given, but the invention is not limited to these examples.

  Since the average particle size of the balls 4 varies depending on the type of raw material, it cannot be determined unconditionally. Therefore, it is desirable to determine the average particle diameter of the balls 4 according to the type of material to be processed. Usually, the average particle diameter of the balls 4 is preferably 3.0 mm or more, more preferably 5.0 mm or more, from the viewpoint of uniformly performing mechanical milling on the powder particles 3. From the viewpoint of ensuring ease of operation, it is preferably 10 mm or less, more preferably 7.0 mm or less.

  The container 5a is preferably made of a material that can suppress the contamination of impurities derived from the container 5a. As such a material, the material similar to the material of the above-mentioned ball 4 is illustrated.

  The mass ratio between the powder particles 3 and the balls 4 put into the container 5a varies depending on the type of raw material, the type and size of the balls 4, and therefore cannot be determined unconditionally. Therefore, it is desirable that this ratio is appropriately determined according to the type of raw material, the type and size of the ball 4. Usually, the mass ratio is powder particles / ball = 1/10 to 1/2 from the viewpoint of uniformly performing mechanical milling on the powder particles 3.

The mechanical milling process is performed by putting the powder particles 3 and the balls 4 into the container 5a of the ball mill apparatus 5, and then rotating the ball mill apparatus 5 after sealing the container 5a.
As shown in FIG. 2, the mechanical milling process may use a planetary ball mill device 5 or other commercially available mechanical alloying device.
The processing time, processing temperature, processing atmosphere, and the like of the mechanical milling process may be sufficient as long as the powder particles 3 are strongly processed. For example, the treatment time affects the cross-sectional area ratio of the surface fine grain structure region 8 of the intermediate particle 6.

  As described later, the surface portion fine grain structure region 8 and the coarse grain structure region 2 of the intermediate particle 6 constitute a fine grain structure region 1 and a coarse grain structure region 2 included in the metal material by sintering. Become. The cross-sectional area ratio of the fine grain structure region 1 of the metal material is preferably 20% or more and 70% or less. In order to form the surface portion fine grain structure region 8 capable of realizing this, mechanical milling is performed. The treatment time for the treatment is preferably set to 10 hours or longer, more preferably 15 hours or longer.

  The processing temperature of the mechanical milling process is not particularly limited, and may be, for example, room temperature (for example, 20 to 30 degrees) or higher than room temperature. The surface of the powder particle 3 becomes active by strong processing. Therefore, from the viewpoint of suppressing the surface of the powder particles 3 from being oxidized, the treatment atmosphere is preferably performed in an inert gas (eg, argon gas) atmosphere.

  As described above, when the intermediate particles 6 are obtained by performing mechanical milling on the powder particles 3, the intermediate particles 6 are then sintered (sintering step).

As shown in FIG. 3 (c), by sintering the intermediate particles 6 (FIG. 3 (b)), the surface fine particle structure regions 8 on the surface of each intermediate particle 6 are bonded together to form a metal material. . At this time, in the metal structure of the metal material, the fine grain structure region 1 having a network structure is formed by bonding the surface fine grain structure regions 8 of the intermediate particles 6 to each other.
In addition, the coarse grain structure region 2 included in each intermediate particle is arranged inside the mesh of the fine grain structure region 1 because the surface fine grain structure region 8 becomes the fine grain structure region 1 of the network structure. And dispersed in the fine grain structure region 1.

  That is, the surface fine-grain structure region 8 of the intermediate particles 6 is formed as the fine-grain structure region 1 of the sintered metal material, and the coarse-grain structure region 2 of the intermediate particles 6 is the inside of the mesh of the fine-grain structure region 1. Is included in the metal structure of the sintered metal material.

  By sintering the intermediate particles 6 as described above, the surface fine grain structure regions of the intermediate particles 6 are bonded to each other, and the metal structure is bonded to the surface fine particle structure regions 8 to each other. And a plurality of coarse grain structure regions 2 included in the intermediate particles 6, and the plurality of coarse grain structure regions 2 are inside the mesh of the fine grain structure region 1. The metal material arrange | positioned in is formed.

  The sintering step can be performed using a discharge plasma sintering apparatus 20 shown in FIG. The discharge plasma sintering apparatus 20 includes a vacuum water cooling chamber 21, a die 22, upper and lower punches 23 and 24 inserted into the die 22, and a power source 25. The discharge plasma sintering apparatus 20 heats the punches 23 and 24 by applying a direct-current pulse current from a power supply 25, and at the same time, vacuum-cooled chamber 21 in which the powder filled in the die 22 is conditioned. It is comprised so that it may press and sinter with both punches 23 and 24 inside.

  The intermediate particles 6 are filled into the die 22 as it is or pressed into a predetermined shape. The intermediate particles 6 filled in the die 22 are pressurized by the upper and lower punches 23 and 24, and further heated and sintered by a direct current pulse current applied to both the punches 23 and 24.

FIG. 4 is a diagram illustrating an example of sintering conditions in the sintering process. In the sintering step, heating is started by heating and pressurization is started via both punches 23 and 24, and the temperature is raised so that a predetermined holding pressure P is reached when a predetermined holding temperature T is reached. Set the speed and boost speed.
Thereafter, the holding temperature T and the holding pressure P are held for a predetermined holding time H. After the holding time H elapses, the temperature is lowered and lowered at a predetermined temperature lowering rate and step-down rate.

  As will be described later, the rate of temperature rise and the holding temperature T are different from the solid phase of the fine crystal grains 1a constituting the fine grain structure region 1 before the temperature rise. It is determined in consideration of precipitation in the metal structure. From the viewpoint of precipitating other solid-phase crystal grains, the rate of temperature rise is preferably set to 0.8 to 1.7 K / s.

  In order to precipitate other solid phase crystal grains, for example, it is conceivable to pass a temperature at which the raw material starts solid phase transformation when the temperature is raised. In this case, the holding temperature T needs to be set to be equal to or higher than the temperature at which the raw material starts solid phase transformation.

For example, in the case of a Co-28Cr-6Mo alloy (for example, ASTM-F75), the HCP phase that is a stable phase at room temperature at about 1200 K (phase that is a hexagonal close-packed crystal structure, also referred to as ε phase) Then, solid phase transformation is started in the FCC phase which is a metastable phase (phase whose crystal structure is a face-centered cubic structure, also called α phase).
Also, in the case of Ti-6Al-4V alloy (for example, JIS 60 type), the HCC phase (also referred to as α phase) which is a stable phase at room temperature is about 1200 K, and the BCC phase (crystal) which is a metastable phase at room temperature. A solid phase transformation is initiated in a phase whose structure is a body-centered cubic structure (also called a β phase).
Furthermore, in 18Cr-8Ni stainless steel (for example, JIS SUS304 etc.), the treatment temperature of the solution heat treatment, which is a treatment for dissolving each component in the austenite phase, is generally maintained at about 1173 to 1473K.

  Furthermore, it is necessary to consider that the holding temperature T is higher than the temperature at which the intermediate particles 6 can be sufficiently sintered, and that the holding temperature T needs to be suppressed to a temperature at which the crystal grains of the metal material are not coarsened. Considering the above viewpoint, the holding temperature T is appropriately set in the range of 1173 to 1473K according to the alloy used as the raw material.

The holding pressure P is preferably set to 30 to 200 MPa from the viewpoint of the density of the metal material to be obtained and the allowable pressure of the die 22 and the punches 23 and 24 used for sintering.
The holding time H is preferably set to 1.8 to 5.4 Ks from the viewpoint of suppressing the coarsening of the crystal grains of the metal material.

  The step-down rate is appropriately set according to the temperature-decreasing rate, but is usually preferably set to 1 to 2 MPa / s.

  The temperature lowering rate is appropriately set from the viewpoint of controlling the structure of the fine grain structure region 1 described later. If the temperature is lowered at a relatively high speed, a metal material having a higher proportion of metastable phase than stable phase can be obtained. Therefore, by lowering the temperature at a sufficiently high speed, a metal material that is substantially metastable and single phase can be obtained. In addition, the lower the rate of temperature decrease, the greater the proportion of stable phase. The temperature drop rate adjustment performed when adjusting the ratio of the metastable phase varies depending on the type of raw material, but can be set to 0.5 to 6 K / s, for example.

  Further, the atmosphere in the vacuum water cooling chamber 21 in which the intermediate particles 6 are pressurized and sintered is adjusted to a vacuum atmosphere (for example, 15 Pa or less). Thereby, it is possible to suppress the formation of significant pores or the like in the metal material after the intermediate particles 6 are sintered.

  FIG. 5 is a diagram showing changes in crystal grains in the fine grain structure region 1 of the metal material in the sintering process. This FIG. 5 demonstrates the case where a Ti-6Al-4V alloy is used as a raw material of the powder particle 3. FIG.

In the Ti-6Al-4V alloy, as described above, at about 1200 K, the solid phase transformation starts from the HCP phase that is a stable phase at room temperature to the BCC phase that is a metastable phase at room temperature.
FIG. 5A is a diagram showing the relationship between the temperature condition in the sintering process and the temperature at which transformation starts. As shown in the figure, when a Ti-6Al-4V alloy is used, the holding temperature T is set in the region of the BCC phase and passes through the transformation start temperature for starting the solid phase transformation from the HCP phase to the BCC phase. The temperature conditions are set as follows. Therefore, the temperature in the sintering process is raised from the HCP single-phase region to the two-phase region of the HCP phase and the BCC phase and the BCC single-phase region, and after reaching the holding temperature T, the temperature is held for the holding time H. Thereafter, the temperature is lowered by cooling at a predetermined temperature lowering rate.

FIG. 5B is a diagram showing changes in crystal grains of the fine grain structure region 1 in the temperature region of each phase.
As shown in the figure, the crystal grains near the surface of the powder particles before mechanical milling (before MM) in the Ti-6Al-4V alloy are composed of relatively coarse crystal grains. At this time, the Ti-6Al-4V alloy is substantially a single phase of the HCP phase.
The crystal grains near the surface of the powder particles are then refined by a mechanical milling process to form a surface portion fine grain structure region 8.

  In the HCP single phase region after the mechanical milling process (after MM) and below the transformation start temperature, the fine grain structure region 1 (surface portion fine grain structure region 8) is a fine crystal grain refined by the mechanical milling process. It is configured. In the Ti-6Al-4V alloy, the crystal grains maintain the HCP phase even after being refined by mechanical milling. Therefore, the fine grain structure region 1 in this case is composed of crystal grains of the HCP phase.

After the mechanical milling process, when the temperature is raised from room temperature and passes through the HCP single phase region, and passes through the transformation start temperature and reaches the two phase region, precipitation of BCC phase crystal grains occurs in the fine grain structure region 1. Arise. That is, the fine grain structure region 1 in the two-phase region has a two-phase structure of fine crystal grains of the HCP phase and precipitated fine crystal grains of the BCC phase. As a result, the crystal grains are further refined as the entire fine grain structure region 1.
At this time, the BCC phase crystal grains are also precipitated in the coarse grain structure region 2, but the HCP phase crystal grains originally constituting the coarse grain structure region 2 are coarse so that they are not greatly affected.

When the temperature is further increased, the phase passes through the two-phase region, reaches the BCC single-phase region, and is held at the holding temperature T, the fine grain structure region 1 becomes a single-phase structure composed of BCC phase crystal grains. At this time, each crystal grain in the fine grain structure region 1 may be coarsened by being held at the holding temperature T belonging to the BCC single phase region.
In this respect, as described above, in addition to the fact that the crystal grains are further refined as a whole by the crystal grains newly precipitated by passing the transformation start temperature, the holding temperature T is set to the BCC single phase. By maintaining the temperature as low as possible in the region, the coarsening of each crystal grain in the fine grain structure region 1 is suppressed.
At this time, the coarse grain structure region 2 also has a single-phase structure composed of BCC phase crystal grains, but the coarse crystal grains are maintained by being maintained as it is.

After that, when the temperature is lowered and the HCP single phase region is reached again, the fine grain structure region 1 becomes a structure that maintains a state composed of fine crystal grains. At this time, the fine grain structure region 1 is substantially composed of fine crystal grains of the HCP phase, but some of the crystal grains of the BCC phase can remain depending on the temperature lowering condition. In this case, the fine grain structure region 1 has a two-phase structure including two types of crystal grains having different crystal structures.
Further, the coarse grain structure region 2 has a structure composed of coarse crystal grains of the HCP phase.

  In the Ti-6Al-4V alloy as a metal material obtained by sintering as described above, a fine grain structure region 1 having a network structure and a plurality of the fine grain structure areas 1 arranged inside the network. It is possible to make a metal structure including the coarse grain structure region 2.

  According to the manufacturing method having the above configuration, the solid phase is different from the HCP phase that is the solid phase of the fine crystal grains constituting the fine grain structure region 1 before the temperature increase due to the temperature increase in the sintering step. Since the crystal grains of the BCC phase are precipitated, the fine grain structure region 1 can be made a metal structure composed of finer crystal grains. As a result, even if the crystal grains grow somewhat by being held at a higher temperature after that, it is possible to suppress coarsening of the fine crystal grains constituting the fine grain structure region.

  FIG. 6 is a diagram showing another example showing changes in crystal grains in the fine grain structure region 1 of the metal material in the sintering process. This FIG. 6 demonstrates the case where a Co-28Cr-6Mo alloy is used as a raw material of the powder particle 3. FIG.

Also in the Co-28Cr-6Mo alloy, solid phase transformation is started at about 1200 K from the HCP phase, which is a stable phase at normal temperature, to the FCC phase, which is a metastable phase at normal temperature.
FIG. 6A is a diagram showing the relationship between the temperature condition in the sintering process of this example and the temperature at which transformation starts. As shown in the figure, when a Co-28Cr-6Mo alloy is used, the holding temperature T is set in the FCC phase region, and passes through the transformation start temperature at which solid phase transformation starts from the HCP phase to the FCC phase. The temperature conditions are set as follows. Therefore, the temperature in the sintering process is raised from the HCP single-phase region to the two-phase region of the HCP phase and the FCC phase, and the FCC single-phase region. After reaching the holding temperature T, the temperature is held for the holding time H. Thereafter, the temperature is lowered by cooling at a predetermined temperature lowering rate.

FIG.6 (b) is a figure which shows the change of the crystal grain of the fine grain structure area | region 1 in the temperature area | region for every phase in this example.
Here, the case where the powder particles 3 made of the Co-28Cr-6Mo alloy before the mechanical milling process contain a lot of crystal grains of the FCC phase which is a metastable phase as described above is shown. Yes.

As shown in the figure, the crystal grains in the vicinity of the powder particle surface before mechanical milling (before MM) in the Co-28Cr-6Mo alloy are composed of relatively coarse crystal grains. At this time, the Co-28Cr-6Mo alloy contains many crystal grains of the FCC phase which is a metastable phase. In addition, as shown in the figure, the crystal grains of the HCP phase which is a slightly stable phase may be included.
The crystal grains near the surface of the powder particles are then refined by a mechanical milling process to form a surface portion fine grain structure region 8.

In the HCP single phase region after the mechanical milling process (after MM) and below the transformation start temperature, the fine grain structure region 1 (surface portion fine grain structure region 8) is a fine crystal grain refined by the mechanical milling process. It is configured. Further, as described above, the Co-28Cr-6Mo alloy that is a metastable phase undergoes processing-induced martensitic transformation on the surface thereof by mechanical milling, and transforms into an HCP phase that is a stable phase. Therefore, the fine grain structure region 1 in this case is substantially composed of fine crystal grains of a single HCP phase.
That is, as shown in the figure, even if the surface before MM has two phases of FCC phase and HCP phase, it can be substantially made into HCP phase single phase fine crystal grains by mechanical milling treatment. .

After the mechanical milling process, when the temperature is raised from room temperature and passes through the HCP single phase region, and passes through the transformation start temperature and reaches the two phase region, precipitation of FCC phase crystal grains occurs in the fine grain structure region 1. Arise. That is, the fine grain structure region 1 in the two-phase region has a two-phase structure of fine crystal grains of the HCP phase and precipitated fine crystal grains of the FCC phase. As a result, the crystal grains become finer as a whole in the fine grain structure region 1 and the coarsening of the HCP phase crystal grains is suppressed by the newly precipitated FCC phase crystal grains.
At this time, since the coarse grain structure region 2 is already composed of crystal grains of the FCC phase, the two-phase region is not greatly affected.

When the temperature is further increased, the two-phase region is reached, the FCC single-phase region is reached and the holding temperature T is maintained, the fine-grained structure region 1 becomes a single-phase structure composed of FCC phase crystal grains. At this time, each crystal grain in the fine grain region 1 may be coarsened by being held at the holding temperature T belonging to the FCC single phase region.
However, in this case, in addition to the fact that the crystal grains are further refined as a whole by the crystal grains newly precipitated by passing the transformation start temperature, the holding temperature T is set within the FCC single-phase region. By keeping the temperature as low as possible, the coarsening of each crystal grain in the fine grain structure region 1 is suppressed.
At this time, the coarse grain structure region 2 also has a single-phase structure composed of FCC phase crystal grains, but the coarse crystal grains are maintained by being maintained as it is.

After that, when the temperature is lowered and the HCP single phase region is reached again, the fine grain structure region 1 becomes a structure that maintains a state composed of fine crystal grains.
Here, when the Co-28Cr-6Mo alloy is cooled and cooled at a predetermined cooling rate from the FCC single phase region, it becomes a structure composed of the FCC phase that is a metastable phase. The FCC phase crystal grain structure may partially include a HCP phase crystal grain. In this case, the fine grain structure region 1 has a two-phase structure including two kinds of crystal grains having different crystal structures (FCC phase crystal grains and HCP phase crystal grains).

  In the Co-28Cr-6Mo alloy as the metal material obtained by sintering as described above, a fine grain structure region 1 having a network structure and a plurality of the fine grain structure areas 1 arranged inside the network. It is possible to make a metal structure including the coarse grain structure region 2.

  Also in the manufacturing method having the above-described structure, the solid phase crystal grains different from the solid phase of the fine crystal grains constituting the fine grain structure region 1 before the temperature rise are precipitated by the temperature rise in the sintering process. The fine grain structure region 1 can be made into a metal structure made of finer crystal grains. As a result, even if the crystal grains are held at a higher temperature and grow somewhat, the fine crystal grains constituting the fine grain structure region 1 can be prevented from becoming coarse.

  For example, when the fine grain structure region 1 is a single phase of the FCC phase in the HCP single phase region, the fine grain structure region 1 is formed even if the temperature is raised from room temperature and passes through the transformation start temperature and reaches the two phase region. Since the fine crystal grains are in the FCC phase, precipitation of crystal grains of different solid phases cannot occur. For this reason, the coarsening of the fine crystal grains cannot be suppressed, and the fine crystal grains constituting the fine grain structure region 1 may be coarsened.

In this regard, in the above production method, the FCC phase present on the surface of the powder particle 3 is transformed into the HCP phase, which is a stable phase, by the mechanical milling process, so that the surface of the powder particle 3 is substantially a single stable phase. The surface portion fine grain structure region 8 is formed into a phase, and is configured to precipitate metastable phase (FCC phase) crystal grains in the fine grain structure region 1 in the sintering step.
In this case, even if the powder particles before the mechanical milling treatment include FCC phase, the portion of the FCC phase existing on the surface of the powder particles 3 is transformed into the HCP phase by the mechanical milling treatment. The surface fine-grain structure region 8 can be substantially a single phase of the HCP phase, and the fine-grain texture region 1 can be substantially a single phase of the HCP phase. For this reason, the crystal grains of the FCC phase can be reliably and uniformly precipitated by increasing the temperature in the sintering step, and the fine grain structure region 1 can be uniformly refined. As a result, coarsening of crystal grains in the fine grain structure region 1 can be suppressed uniformly.

Moreover, in the said manufacturing method, although the case where Ti-6Al-4V alloy and Co-28Cr-6Mo alloy were used as a raw material was illustrated, it is not limited to this, It heats up to sintering temperature. In the process, any alloy material may be used as long as it can precipitate crystal grains of another solid phase different from the solid phase of the fine crystal grains constituting the fine grain structure region 1 before the temperature rise.
More specifically, an alloy that becomes a two-phase by processing-induced transformation or diffusion transformation, an austenitic stainless steel, or a two-phase stainless steel.

An austenitic stainless steel such as 18Cr-8Ni stainless steel is an austenitic phase that is a metastable phase at room temperature, and, like a Co-28Cr-6Mo alloy, when a strong work is applied to the surface by mechanical milling or the like, a processing-induced martensite is obtained. Site transformation occurs and transforms into α ′ phase (BCC phase) which is a stable phase.
Therefore, when austenitic stainless steel is used as a raw material, as in the case of using a Co-28Cr-6Mo alloy, the fine grain structure region 1 on the surface of the powder particle 3 is transformed by a mechanical milling process, and a network structure is obtained. It is possible to obtain a metal structure including the fine grain structure region 1 and a plurality of coarse grain structure regions 2 arranged inside the mesh of the fine grain structure region 1. That is, a metal material can be manufactured by the same manufacturing method as long as it is an alloy that causes remarkable work hardening, such as a Co-28Cr-6Mo alloy or an austenitic stainless steel.

  Further, for example, a shape memory alloy such as a Ni—Ti alloy that causes martensite transformation relatively easily by processing, and a manganese steel that causes remarkable work hardening are also produced by a manufacturing method similar to that for a Co-28Cr-6Mo alloy. Can be manufactured.

  In the above manufacturing method, the case where mechanical milling processing is performed as a strong processing on powder particles and a fine grain structure region is provided on the surface has been shown. For example, a general ball mill, ultrasonic mill, vibration mill, or shot blasting The fine grain structure region can also be provided by other strong working methods capable of miniaturizing the structure by the stress generated by performing fine processing on the surface and capable of inducing transformation.

  Moreover, in the sintering process in the above manufacturing method, the case where powder particles (intermediate particles) are pressed and sintered by discharge plasma sintering has been shown. It may be a result. Further, the heating method is not limited to pulse current heating by discharge plasma, and heating may be performed by other general heat sources.

  Next, the present invention will be described in more detail based on examples and the like, but the present invention is not limited only to such examples.

[Co-28Cr-6Mo alloy]
First, an experimental example when a metal material is manufactured by sintering powder particles made of a Co-28Cr-6Mo alloy will be described.
(Experimental Examples 1-4)
As powder particles, a Co-28Cr-6Mo alloy (equivalent to ASTM-F75) powder (average particle diameter 217 μm) produced by the rotating electrode method was used.
The chemical components of the powder particles of this Co-28Cr-6Mo alloy are as shown in Table 1 below, and it can be confirmed that the used powder particles are substantially composed of a single alloy.

Powder particles made of the above Co-28Cr-6Mo alloy are made into steel balls (JIS SUJ2).
And an average particle diameter of 5 mm) were put into a container of a planetary ball mill apparatus (manufactured by Fritsch, trade name: P-5 type). The treatment conditions were as follows: argon atmosphere, room temperature, ball: powder particles = 2: 1 (mass ratio), rotation speed 200 rpm, treatment time 0 ks (Experiment 1), 54 ks (Experiment 2), 90 ks (Experiment 3), 180 ks. As Experimental Example 4, mechanical milling was performed on the powder particles of the Co-28Cr-6Mo alloy to obtain intermediate particles.

(Test Example 1)
The appearance of the intermediate particles obtained in Experimental Examples 1 to 4 was observed with SEM (trade name: FE-SEM S-4800, manufactured by Hitachi High-Technologies Corporation).
7A and 7B are diagrams showing the observation results of the intermediate particles obtained in Test Example 1. FIG. 7A shows the observation results of the intermediate particles obtained in Experimental Example 1, and FIG. 7B shows the intermediate results obtained in Experimental Example 2. The observation results of the particles, (c) are the observation results of the intermediate particles obtained in Experimental Example 3, and (d) are the observation results of the intermediate particles obtained in Experimental Example 4.

The state in which the particle diameter of each intermediate particle is extremely reduced by the processing time of the mechanical milling process is not seen.
As shown in FIG. 7 (a), many linear patterns are observed on the particle surface of the particles not subjected to mechanical milling (processing time 0ks: Experimental Example 1). As shown in d), after the mechanical milling treatment (Experimental Examples 2 to 4), no linear pattern is seen on the particle surface, which is a satin finish, and by mechanical milling treatment, It can be confirmed that strong processing is performed over the entire surface.

(Test Example 2)
The intermediate particles obtained in Experimental Examples 1 to 4 were subjected to qualitative analysis by measuring diffraction patterns using an X-ray diffractometer (trade name: RINT2000, manufactured by Rigaku Corporation).
FIG. 8 is a diagram showing an X-ray diffraction pattern of an intermediate particle according to Test Example 2, in which the lowermost row shows that mechanical milling treatment is not performed (processing time 0 ks: Experimental Example 1), and the uppermost row shows mechanical milling. It is a figure which shows the thing after processing (processing time 54ks: Experimental example 2). The second and third stages from the bottom show X-ray diffraction patterns with mechanical milling time of 0.6 ks and 3.6 ks.

  In the case where mechanical milling treatment is not performed (treatment time 0 ks: Experimental Example 1), only the peak of the FCC phase (α phase) is seen, and the peak of the HCP phase (ε phase) can hardly be confirmed.

  From the X-ray diffraction pattern when the mechanical milling time is 0.6 ks, it can be seen that the HCP phase peak appears together with the FCC phase peak. Further, it can be seen that the peak intensity of the HCP phase is relatively larger than the peak intensity of the FCC phase as the processing time of the mechanical milling process is increased.

In general, when mechanical milling treatment is performed on the surface of powder particles of a Co-28Cr-6Mo alloy, work-induced martensite is generated in that portion and an HCP phase appears.
That is, from the above results, it can be confirmed that the FCC phase present on the surface of the powder particle is transformed into a stable HCP phase (processing induced martensite) by performing mechanical milling on the surface of the powder particle. .

FIG. 9 is a diagram illustrating an X-ray diffraction pattern of intermediate particles according to Test Example 2, and illustrates X-ray diffraction patterns according to Experimental Examples 1 to 4.
Compared with Experimental Example 1 in which mechanical milling treatment is not performed, the X-ray diffraction patterns of Experimental Examples 2 to 4 in which mechanical milling treatment is performed appear such that the peak width is widened. Further, as the processing time of the mechanical milling process increases, the peak width gradually increases.
This seems to be because random strain is introduced into the crystal structure of the surface portion of the powder particles by the mechanical milling process. Therefore, also from this point, by performing mechanical milling on the surface of the powder particles, it can be confirmed that the surface of the powder particles is strongly processed to induce phase transformation.

(Experimental example 5)
The intermediate particles obtained in Experimental Example 1 were filled into a mold constituted by a cylindrical die and a punch having the following dimensions.
Die: Outer diameter 30mm, Inner diameter 15.2mm, Axial length 30mm
Punch: outer diameter 15mm, axial length 20mm

  The intermediate particles filled in the mold are baked under a predetermined temperature condition and pressure condition under a vacuum (15 Pa>) with a discharge plasma sintering apparatus (manufactured by Syntex Co., Ltd., trade name: DR.SINTER-1020). As a result, a disk-shaped sintered body (metal material) having a thickness of 2.5 to 5.5 mm and a diameter of 15 mm was obtained.

  FIG. 10 is a diagram illustrating temperature conditions and pressure conditions in Experimental Example 5. As shown in the figure, the temperature condition is that the temperature is increased at a rate of temperature increase of 1.17 K / s and maintained such that the retention temperature T is 1323 K and the retention time H is 3.6 ks, and then the temperature decrease rate is 1.1 K / s. s (set value of control program) was set to cool down. Further, the pressure condition is such that the holding pressure P is increased to 50 MPa when reaching 1323 K under the above temperature condition, and is maintained at 50 MPa for the holding time H, and then the pressure reduction rate is 1.7 MPa / s. It was set to step down.

(Experimental Examples 6 to 8)
Using the intermediate particles obtained in Experimental Example 2, the same operation as in Experimental Example 5 was performed to obtain a disk-shaped sintered body (Experimental Example 6). Similarly, the same operations as in Experimental Example 5 were performed using the intermediate particles obtained in Experimental Example 3 to obtain a disk-shaped sintered body (Experimental Example 7). Using the intermediate particles obtained in Experimental Example 4, the same operation as in Experimental Example 5 was performed to obtain a disk-shaped sintered body (Experimental Example 8).

(Test Example 3)
The metal material obtained in Experimental Examples 5 to 8 was cut to obtain test pieces. After embedding this test piece in a resin, the cut surface is mirror-polished, and then an EBSD (Electron Back Scattering Pattern Pattern) detector (trade name: NordlysNano) manufactured by Oxford Instruments Co., Ltd. is used. The crystal grains in each metal material were observed.

  FIG. 11 is a diagram showing a crystal grain boundary map in each metal material in Test Example 3, wherein (a) is a crystal grain boundary map of the metal material obtained in Experimental Example 5, and (b) is Experimental Example 6. (C) is a crystal grain boundary map of the metal material obtained in Experimental Example 7, and (d) is a crystal grain boundary map of the metal material obtained in Experimental Example 8. It is a map. In the figure, the scale bar indicates 100 μm.

As shown in FIG. 11A, in the cross-sectional structure of the sintered product (Experimental Example 5) that is not subjected to mechanical milling treatment, relatively coarse crystal grains and fine crystals as compared with coarse crystal grains. Seen with grains.
It can be seen that the relatively coarse crystal grains (coarse crystal grains) form a plurality of circular aggregates, and are the crystal grains constituting the original powder particles. Relatively fine crystal grains (fine crystal grains) occupy a small proportion compared to other experimental examples, and exist partially between aggregates composed of a plurality of coarse crystal grains. .
Thus, the metal material which concerns on the experiment example 5 sintered without performing a mechanical milling process does not have the fine grain structure area | region made into network structure.

As shown in FIGS. 11B to 11D, in the cross-sectional structure of the sintered product after performing the mechanical milling process (Experimental Examples 6 to 8), a fine grain structure region constituted by fine crystal grains is shown. And a plurality of coarse grain structure regions composed of coarse crystal grains.
It can be seen that the plurality of coarse grain structure regions are dispersed in the fine grain structure region, and the fine grain structure region has a network structure.

11B to 11D, as the processing time of the mechanical milling process is increased, the size of each coarse grain structure region is reduced, and the area occupied by the coarse grain structure region is gradually reduced. You can see that
The coarse grain structure region corresponds to an aggregate of a plurality of coarse crystal grains in FIG. 11 (a), and among the crystal grains constituting the intermediate grains before sintering, a mechanical portion is provided at the center of the intermediate grains. This is the part that was not affected by the milling process. On the other hand, the fine grain structure region which is a network structure is a part where the surface fine grain structure regions formed by mechanical milling on the surface of each intermediate particle before sintering are bonded to each other by sintering.

  Therefore, as the processing time of the mechanical milling process becomes longer, the size of each coarse grain structure area becomes smaller and the area occupied by the fine grain structure area gradually increases, so the surface of the intermediate particles before sintering The proportion of the fine grain structure region increases as the processing time of the mechanical milling process increases, and conversely, the coarse grain structure region in the center of the intermediate particle increases as the processing time of the mechanical milling process increases. It can be seen that the proportion occupied was small.

  Moreover, it turns out that the ratio for which a fine grain structure area | region occupies, and the ratio for which a coarse grain structure area | region occupy can be adjusted by adjusting the processing time of a mechanical milling process from the said result.

(Test Example 4)
The image data of the grain boundary map obtained in Test Example 3 was processed using image analysis software (trade name: EBSD analysis software AZtecHKL manufactured by Oxford Instruments Co., Ltd.), and obtained in Experimental Examples 5 to 8. The cross-sectional area ratio of the fine grain structure region of each metal material was determined. Further, the average crystal grain size of the fine crystal grains constituting the fine grain structure region and the average crystal grain size of the coarse crystal grains constituting the coarse grain structure region were determined.

FIG. 12A is a graph showing the relationship between the cross-sectional area ratio of the fine grain structure region and the processing time of the mechanical milling process.
In the figure, the cross-sectional area ratio of the fine grain structure region of Experimental Example 6 is 57.3%, the cross-sectional area ratio of the fine grain structure area of Experimental Example 7 is 65.8%, and the fine grain structure area of Experimental Example 8 The cross-sectional area ratio was 79.2%.
Thus, it can be confirmed that the longer the processing time of the mechanical milling process, the higher the cross-sectional area ratio of the fine grain structure region.

FIG. 12B is a graph showing the relationship between the average crystal grain size of the crystal grains constituting the fine grain structure region and the coarse grain structure region and the processing time of the mechanical milling process.
In the figure, the average crystal grain size of the coarse crystal grain of Experimental Example 5 is 36.8 μm, the average crystal grain size of the coarse crystal grain of Experimental Example 6 is 37.6 μm, and the average crystal grain of the coarse crystal grain of Experimental Example 7 The diameter is 36.4 μm, the average crystal grain size of the coarse crystal grains of Experimental Example 8 is 33.1 μm, and the coarse crystal grains constituting the coarse grain structure region are slightly smaller depending on the processing time of the mechanical milling process. You can see that
On the other hand, the fine crystal grains constituting the fine grain structure region are 3.2 μm in Experimental Example 6, 3.1 μm in Experimental Example 7, and 3.1 μm in Experimental Example 8, and are approximately regardless of the processing time of the mechanical milling process. It can be seen that it is almost constant at 3 μm.

  FIG. 13 is a Co—Cr binary state diagram. Since the Co-28Cr-6Mo alloy used in Experimental Examples 5 to 8 contains 27.73% by weight of Cr, when sintering is performed under the temperature condition shown in FIG. 927 ° C.) From a single-phase region of HCP phase, which is a stable phase at K, to a two-phase region starting from a metastable FCC phase at room temperature to become a two-phase region, at a little over 1200K, from the two-phase region to FCC A single-phase region is reached. Further, during the holding time H, it is held in the FCC single phase region.

  Therefore, in Experimental Examples 6 to 8, the FCC phase on the surface of the powder particles was transformed into an HCP phase that is a stable phase by mechanical milling treatment, so that the surface of the powder particles was substantially made a single phase of the HCP phase. The fine grain structure region is formed, and in sintering, the FCC phase is formed in the fine grain structure region which is made into a single phase of the HCP phase by mechanical milling by raising the temperature so as to pass the transformation start temperature. Crystal grains are precipitated. Thereby, the fine grain structure region becomes a metal structure composed of finer crystal grains.

  Thereby, even if it hold | maintains by the higher holding temperature T after that, as shown to FIG.11 (b)-(d) and FIG.12 (b), the average crystal | crystallization of the fine crystal grain which comprises a fine grain structure area | region The particle size is approximately 3 μm and is almost constant, and the coarsening of the fine crystal grains constituting the fine grain structure region is suppressed.

  In addition, since the fine grain structure region is made into a single phase of the HCP phase by mechanical milling treatment, the crystal grains of the FCC phase can be uniformly precipitated in the fine grain structure region by increasing the temperature during sintering. The tissue region is uniformly refined. As a result, the coarsening of crystal grains in the fine grain structure region is uniformly suppressed.

(Test Example 5)
Using a micro Vickers hardness meter (manufactured by Shimadzu Corporation, trade name: HMV-2), cross-sectional hardness measurement was performed for each of the metal materials obtained in Experimental Examples 5 to 8 according to JIS Z2244.
A micro Vickers hardness test was performed on the cut surface of the test piece prepared in Test Example 3 with a test load of 980.7 mN and a holding time of 5 s.

  FIG. 14 is a diagram for explaining measurement points in the micro Vickers hardness test. As shown in FIG. 14, 100 measurement points arranged linearly at 20 μm intervals are set as measurement points in an arbitrary region within the cut surface of one test piece, and the cross-sectional hardness of each measurement point is set. Was measured.

FIG. 15 is a diagram illustrating a measurement result of the cross-sectional hardness of each metal material according to Test Example 5, and is a diagram illustrating an average value of cross-sectional hardness measurement values of each of Experimental Examples 5 to 8 and a width of the value. .
The metal material sintered without mechanical milling (Experimental Example 5) has an average cross-sectional hardness of 403 HV, and the cross-sectional hardness is lower than that of other experimental examples. This is because in Experimental Example 5, as shown in FIG. 11A, there is almost no fine grain structure region, and most of the metal structure is composed of coarse crystal grains.
The average value of the cross-sectional hardness of Experimental Example 6 was 429 HV, the average value of the cross-sectional hardness of Experimental Example 7 was 458 HV, and the average value of the cross-sectional hardness of Experimental Example 8 was 471 HV. From these, it is clear that the average value of the cross-sectional hardness increases as the processing time of the mechanical milling process increases. Thereby, it turns out that intensity | strength is raised if the cross-sectional area ratio of a fine grain structure area | region becomes high.

  FIG. 16 is a frequency distribution graph regarding the measurement results of the cross-sectional hardness of each of Experimental Examples 5 to 8 according to Test Example 5. In the figure, the vertical axis shows the relative frequency when the numerical value of the cross-sectional hardness is set to every “10”, and the horizontal axis shows the value of the cross-sectional hardness every the numerical value “10”. Yes.

In FIG. 16, the metal material (Experimental Example 5) sintered without performing mechanical milling is uniformly and widely dispersed in the range of 350 HV to 480 HV.
In the metal materials sintered after mechanical milling (Experimental Examples 6 to 8), the average value of the cross-sectional hardness increases as the processing time of the mechanical milling increases, and the distribution of the cross-sectional hardness is two. Divide into groups.

The reason why the distribution of the cross-sectional hardness is divided into two groups is that, as shown in FIG. 11, in Experimental Examples 6 to 8, a fine grain structure region and a coarse grain structure region exist. Of the two groups in the hardness distribution, the higher value indicates the cross-sectional hardness of the fine grain structure region, and the lower value indicates the cross-sectional hardness of the coarse grain structure region.
Moreover, the cross-sectional hardness of a fine grain structure area | region and the cross-sectional hardness of a coarse grain structure area | region do not change with respect to the change of the processing time of a mechanical milling process.

  Further, as shown in FIG. 16, as the processing time of the mechanical milling process becomes longer, the degree of cross-sectional hardness of the fine grain structure region having a relatively high hardness value increases. As shown in FIGS. 11 and 12, this is consistent with the fact that the longer the processing time of the mechanical milling process, the higher the cross-sectional area ratio of the fine grain structure region. That is, as shown in FIGS. 11 and 12, the longer the processing time of the mechanical milling process, the larger the area of the fine grain structure region, so the probability of measuring the cross-sectional hardness of the fine grain structure area is higher. This is because it becomes higher.

(Test Example 6)
Using a universal testing machine (manufactured by Shimadzu Corporation, trade name: Autograph AG-1 50 kN), each of the metal materials obtained in Experimental Examples 5 to 8 was subjected to a tensile test until breaking. A test piece having a length of 3 mm, a width of 1 mm, and a thickness of 1 mm was prepared using the metal materials obtained in Experimental Examples 5 to 8, and an initial strain rate was set to 5.6 × 10 ⁻⁴ s ⁻¹ and a tensile test was performed. went.

FIG. 17 is a stress-strain curve obtained by a tensile test according to Test Example 6.
Moreover, FIG. 18 is a figure which shows the relationship between the tensile strength obtained by the tension test, and breaking elongation.

  In the figure, the metal material sintered without mechanical milling (Experimental Example 5) had the lowest tensile strength and was 1201 MPa, but the elongation at break was 24.1%, which was compared with other experimental examples. It was a relatively high value.

  The metal material sintered after performing mechanical milling treatment for 54 ks (Experimental Example 6) has a tensile strength of 1283 MPa, which is higher than that of Experimental Example 5. The elongation at break is 24.3%, which is also higher than that of Experimental Example 5.

  The metal material sintered after performing mechanical milling treatment for 90 ks (Experimental Example 7) has a tensile strength of 1297 MPa, which is higher than that of Experimental Examples 5 and 6. On the other hand, the elongation at break is slightly lower than that of Experimental Example 5 at 22.6%.

  The metal material sintered after performing mechanical milling treatment for 180 ks (Experimental Example 8) has a tensile strength of 1251 MPa, which is higher than that of Experimental Example 5, but slightly lower than that of Experimental Examples 6 and 7. The elongation at break is 13.1%, which is lower than that of Experimental Example 5.

  In this way, by conducting a mechanical milling process on the powder particles and sintering, the metal structure is composed of a fine-grain structure region of a network structure and a coarse-grain structure region arranged inside the network. It can be confirmed that the metal materials according to 6 and 7 can maintain the ductility while increasing the strength as compared with the metal material of Experimental Example 5 which does not have the fine grain region of the network structure.

On the other hand, in the metal material according to Experimental Example 8, the metal structure is composed of a fine grain structure region and a coarse grain structure region, and the strength is increased compared to the metal material of Experimental Example 5, but the ductility is reduced. Yes. This is because, in Experimental Example 8, the proportion of the fine grain structure region having high strength is large, and the hardness and strength are increased, so that the degree of freedom in deformation is reduced.
From this point, it can be seen that the ratio of the fine grain structure region is preferably 70% or less in terms of the cross-sectional area ratio as a range including the cross-sectional area ratio of the fine grain structure region in Experimental Example 7.

(Test Example 7)
A diffraction pattern was measured using an X-ray diffractometer for each of the test pieces of Experimental Examples 5 to 8 created in Test Example 6 before the tensile test and after the tensile test.
FIG. 19 is a diagram showing an X-ray diffraction pattern according to Test Example 7, and shows an X-ray diffraction pattern of a test piece before a tensile test in each of Experimental Examples 5 to 8.
Moreover, FIG. 20 is a figure which shows the X-ray-diffraction pattern by Test Example 7, and has shown the X-ray-diffraction pattern of the test piece after the tension test in each of Experimental Examples 5-8.

  19 and 20, both the peak of the HCP phase is seen together with the peak of the FCC phase, and the metal materials according to Experimental Examples 5 to 8 are composed of the two-phase structure of the FCC phase and the HCP phase. I understand that.

  Further, comparing the X-ray diffraction patterns before and after the tensile test, before the tensile test (FIG. 19), the peak of the (10-11) plane among the peaks of the HCP phase is extremely high in any of Experimental Examples 5 to 8. In contrast to the low state, after the tensile test (FIG. 20), the test pieces of Experimental Examples 6 to 8 remarkably appear. Moreover, about the test piece of Experimental example 5 after a tensile test, there is almost no change with the thing before a tensile test.

From the above results, it can be seen that in Experimental Examples 6 to 8, the FCC phase is transformed into the HCP phase due to plastic deformation by the tensile test.
On the other hand, in Experimental Example 5, it can be seen that almost no phase transformation from the FCC phase to the HCP phase is observed due to plastic deformation by the tensile test.
The metal material according to Experimental Example 5 does not have the fine grain structure region as described above, and the metal materials according to Experimental Examples 6 to 8 have the fine grain structure region. It is inferred that the FCC phase that has been transformed into the HCP phase.

From the above results, the metal materials according to Experimental Examples 6 and 7 are improved in mechanical properties such as tensile strength and ductility as compared with Experimental Example 5 due to the phase transformation from the FCC phase to the HCP phase. I can say that.
That is, from the above results, the phase transformation from the FCC phase to the HCP phase has an influence on the mechanical properties such as tensile strength and ductility, and has a fine grain structure region that is a network structure. Thus, it can be seen that the mechanical properties due to the phase transformation are greatly affected.

[About austenitic stainless steel]
Next, experimental examples when a metal material is manufactured by sintering a powder material made of austenitic stainless steel will be described.
(Experimental Examples 9 to 11)
As the powder particles, 18Cr-8Ni stainless steel (equivalent to JIS SUS304L) powder (average particle size 120 μm) produced by the rotating electrode method was used.
The chemical components of the stainless steel powder particles are as shown in Table 2 below, and it can be confirmed that the used powder particles are substantially composed of a single alloy.

  The powder particles made of stainless steel were put into a container of a planetary ball mill apparatus together with a stainless steel ball (equivalent to JIS SUS304, average particle diameter of 5 mm). The treatment conditions are argon atmosphere, room temperature, ball: powder particles = 2: 1 (mass ratio), rotation speed 200 rpm, treatment time 0 ks (experimental example 9), 180 ks (experimental example 10), 360 ks (experimental example 11), Mechanical milling was performed on the stainless steel powder particles to obtain intermediate particles.

(Test Example 8)
The appearance of the intermediate particles obtained in Experimental Examples 9 and 10 was observed by SEM.
FIG. 21 is a diagram showing the observation results of the intermediate particles according to Test Example 8, wherein (a) shows the observation results of the intermediate particles obtained in Experimental Example 9, and (b) shows the intermediate results obtained in Experimental Example 10. It is an observation result of particles.

When both are compared, it is not seen that the particle size of the intermediate particles is extremely reduced by the mechanical milling treatment.
As shown in FIG. 21 (a), many fine regular patterns are observed on the surface of the particles not subjected to mechanical milling (treatment time 0 ks: Experimental Example 9). As shown in FIG. 4, the particle surface after the mechanical milling process (Experimental Example 10) is a satin finish, and the entire surface is subjected to strong processing by the mechanical milling process. I can confirm.

(Test Example 9)
The cross section of the intermediate particles obtained in Experimental Examples 9 and 10 was observed with SEM. After embedding the intermediate particles obtained in Experimental Examples 9 and 10 in a resin, the resin was polished with water-resistant paper or the like to obtain a cross-section of the intermediate particles.
FIG. 22 is a diagram showing the cross-sectional observation result of the intermediate particle according to Test Example 9, (a) is the observation result of the entire cross-section of the intermediate particle obtained in Experimental Example 9, and (b) is the result of (a). The enlarged observation result of the surface part, (c) is the observation result of the entire cross section of the intermediate particle obtained in Experimental Example 10, and (d) is the enlarged observation result of the surface part of (c).

As shown in FIG. 22 (a), the one not subjected to the mechanical milling process (processing time 0 ks: Experimental Example 9) has a circular shape with a smooth surface shape.
Moreover, as shown in FIG.22 (b), the thing which is not performing the mechanical milling process (processing time 0ks: Experimental example 9) is a range from the surface to a depth direction of about 10-15 micrometers from center part. It has a fine structure.

Looking at FIG. 22 (c), the one after the mechanical milling process (Experimental Example 10) shows a deformation in the surface shape as compared with the one not subjected to the mechanical milling process. It can be confirmed that the surface is strongly processed.
As shown in FIG. 22 (d), after the mechanical milling process, a fine structure different from the central portion appears uniformly on the surface side in a range from the surface to about 5 μm in the depth direction. It can be confirmed.
In FIG. 22D, the cross-sectional hardness of the portion appearing on the surface side as a fine structure different from that of the central portion is measured to be 483 HV, and the cross-sectional hardness of the central portion is measured to be 396 HV. It was.
Since the austenitic stainless steel is an FCC phase (austenite phase: γ phase) which is a metastable phase at room temperature, a microstructure different from the central portion appearing on the surface side in FIG. It is inferred that it is an induced martensite, that is, a BCC phase (α ′ phase) which is a stable phase.
In addition, it is guessed that a center part is the FCC phase which is a metastable phase.

(Experimental example 12)
The intermediate particles obtained in Experimental Example 9 were sintered under vacuum (0.1 MPa>) under predetermined temperature conditions and pressure conditions, and were disk-shaped having a thickness of 2.5 to 5.5 mm and a diameter of 15 mm. A sintered body (metal material) was obtained.
The mold and apparatus used for sintering are the same as in Experimental Example 5.

  FIG. 23 is a diagram illustrating temperature conditions and pressure conditions in Experimental Example 12. As shown in the figure, the temperature condition is that the temperature is raised at a rate of temperature increase of 1.17 K / s and held so that the holding temperature T is 1173 K and the holding time H is 3.6 ks. The temperature was set to cool down at s. Further, the pressure condition is increased so that the holding pressure P becomes 50 MPa when reaching 1173 K under the above temperature condition, and is maintained at 50 MPa during the holding time H, and then the pressure reduction rate is 1.7 MPa / s. It was set to step down.

(Experimental Examples 13 and 14)
Using the intermediate particles obtained in Experimental Example 10, the same operation as in Experimental Example 12 was performed to obtain a disk-shaped sintered body (Experimental Example 13). Similarly, the same operations as in Experimental Example 12 were performed using the intermediate particles obtained in Experimental Example 11 to obtain a disk-shaped sintered body (Experimental Example 14).

(Test Example 10)
The metal materials obtained in Experimental Examples 12 to 14 were cut to obtain test pieces, and the crystal grains in each metal material were observed using an EBSD detector provided in the SEM.

  FIG. 24 is a diagram showing a crystal grain boundary map in each metal material according to Test Example 10, where (a) is a crystal grain boundary map of the metal material obtained in Experimental Example 12, and (b) is Experimental Example 13. (C) is a crystal grain boundary map of the metal material obtained in Experimental Example 14. FIG. In the figure, the scale bar indicates 100 μm.

As shown in FIG. 24A, the cross-sectional structure of the sintered product (Experimental Example 12) that was sintered without performing the mechanical milling process is composed of relatively coarse crystal grains (coarse crystal grains). The fine crystal grains seen in (b) and (c) are not seen.
Thus, the metal material which concerns on Experimental example 12 sintered without performing a mechanical milling process does not have the fine grain structure area | region made into the network structure.

As shown in FIGS. 24B and 24C, in the cross-sectional structure of the sintered product after performing the mechanical milling process (Experimental Examples 13 and 14), a fine grain structure region constituted by fine crystal grains is shown. And a plurality of coarse grain structure regions composed of coarse crystal grains.
It can be seen that the plurality of coarse grain structure regions are dispersed in the fine grain structure region, and the fine grain structure region has a network structure.

24B and 24C, the longer the mechanical milling time, the smaller the size of the coarse grain structure region, and the smaller the area occupied by the coarse grain structure region. I understand.
From the above results, it can be seen that the ratio of the fine grain structure region and the ratio of the coarse grain structure region can be adjusted by adjusting the processing time of the mechanical milling process.

(Test Example 11)
The image data of the crystal grain boundary map obtained in Test Example 10 was processed using image analysis software, and the cross-sectional area ratio of each of the fine grain structure regions of the metal materials obtained in Experimental Examples 12 to 14 was obtained. Further, the average crystal grain size of the fine crystal grains constituting the fine grain structure region and the average crystal grain size of the coarse crystal grains constituting the coarse grain structure region were determined.

FIG. 25A is a graph showing the relationship between the cross-sectional area ratio of the fine grain structure region and the processing time of the mechanical milling process.
In the figure, the cross-sectional area ratio of the fine grain structure region of Experimental Example 13 was 21%, and the cross-sectional area ratio of the fine grain structure region of Experimental Example 14 was 41%.
Thus, it can be confirmed that the longer the processing time of the mechanical milling process, the higher the cross-sectional area ratio of the fine grain structure region.

FIG. 25B is a graph showing the relationship between the average crystal grain size of the crystal grains constituting the fine grain structure region and the coarse grain structure region and the processing time of the mechanical milling process.
In the figure, the average crystal grain size of the coarse crystal grain of Experimental Example 12 is 19.7 μm, the average crystal grain size of the coarse crystal grain of Experimental Example 13 is 16.9 μm, and the average crystal grain of the coarse crystal grain of Experimental Example 14 A diameter is 17.6 micrometers and it turns out that the coarse crystal grain which comprises a coarse-grain structure area | region has become small a little according to the processing time of a mechanical milling process.
On the other hand, the average crystal grain size of the fine crystal grains constituting the fine grain structure region is 2.0 μm in Experimental Example 13 and 1.5 μm in Experimental Example 14, and it can be seen that there is no significant difference between the two.

The stainless steel used in Experimental Examples 12 to 14 is equivalent to SUS304, the temperature of the solution heat treatment is 1283 to 1423K according to JIS G4303, and the holding temperature T of 1173K is considered to be an austenite single phase region. .
Therefore, when sintering is performed under the temperature condition shown in FIG. 23, the α phase region reaches the γ phase (austenite phase) region, and the holding temperature T is reached.

  Therefore, in Experimental Examples 13 and 14, the FCC phase, which is a metastable phase on the surface of powder particles, is transformed into a BCC phase (α ′ phase), which is a stable phase, by mechanically milling to transform it into a work-induced martensite, It forms a fine-grained texture region that is essentially a single phase of the BCC phase (α ′ phase) on the surface of the powder particles. In sintering, the BCC phase (α phase) changes to the FCC phase (γ phase). By raising the temperature so as to pass the transformation start temperature for transformation, crystal grains of the FCC phase (γ phase) are precipitated in the fine grain structure region that has been made into the BCC phase (α ′ phase) by mechanical milling treatment. Thereby, the fine grain structure region becomes a metal structure composed of finer crystal grains.

  As a result, even if it is held at a higher holding temperature T after that, as shown in FIGS. 24B and 24C, the average crystal grain size of the fine crystal grains constituting the fine grain structure region is about 1 The coarsening of the fine crystal grains constituting the fine grain structure region is suppressed.

  In addition, since the fine grain structure region is made into a single phase of the BCC phase by mechanical milling treatment, the FCC phase crystal grains can be uniformly precipitated in the fine grain structure region by increasing the temperature during sintering. The tissue region is uniformly refined. As a result, the coarsening of crystal grains in the fine grain structure region is uniformly suppressed without unevenness.

(Test Example 12)
Using a universal testing machine, each of the metal materials obtained in Experimental Examples 12 to 14 was subjected to a tensile test until breaking.

  FIG. 26 is a diagram showing the relationship between the tensile strength obtained by the tensile test in Test Example 12 and the elongation at break.

  In the figure, the metal material sintered without mechanical milling (Experimental Example 12) has a tensile strength of about 570 MPa and a breaking elongation of about 60%, which is higher than the other experimental examples. Are the lowest values.

  The metal material (Experimental Example 13) sintered after performing the mechanical milling process for 180 ks has a tensile strength of about 670 MPa, which is higher than that of Experimental Example 12. The elongation at break is about 80%, which is also higher than that of Experimental Example 12.

  The metal material sintered after the mechanical milling process of 360 ks (Experimental Example 14) has an elongation at break of 80%, which is equivalent to Experimental Example 13, but has a tensile strength of about 740 MPa, compared with Experimental Example 13. It can be seen that it is even higher.

  In this way, by conducting a mechanical milling process on the powder particles and sintering, the metal structure is composed of a fine-grain structure region of a network structure and a coarse-grain structure region arranged inside the network. It can be confirmed that the metal materials according to Nos. 13 and 14 can maintain the ductility while increasing the strength as compared with the metal material of Experimental Example 12 which does not have the fine grain structure region of the network structure.

[Ti-6Al-4V alloy]
Next, an experimental example when a metal material is manufactured by sintering a powder material made of a Ti-6Al-4V alloy will be described.
(Experimental Examples 15 and 16)
As powder particles, powder of Ti-6Al-4V alloy (corresponding to JIS 60 type) manufactured by the rotating electrode method (average particle size 210 μm) was used.

  The powder particles made of the Ti-6Al-4V alloy were put into a container of a planetary ball mill apparatus together with a steel ball (equivalent to JIS SUJ2 and an average particle diameter of 9.5 mm). The treatment conditions were argon atmosphere, room temperature, ball: powder particles = 2: 1 (mass ratio), rotation speed 200 rpm, treatment time 0 ks (Experimental Example 15), 90 ks (Experimental Example 16), and Ti-6Al-4V alloy The powder particles were subjected to mechanical milling to obtain intermediate particles.

(Test Example 13)
The appearance of the intermediate particles obtained in Experimental Examples 15 and 16 was observed by SEM.
27 is a diagram showing the observation results of the intermediate particles in Test Example 13, where (a) shows the observation results of the intermediate particles obtained in Experimental Example 15, and (b) shows the intermediate results obtained in Experimental Example 16. FIG. It is an observation result of particles.

When both are compared, it is not seen that the particle size of the intermediate particles is extremely reduced by the mechanical milling treatment.
As shown in FIG. 27A, the particle surface of the sample not subjected to the mechanical milling process (processing time 0 ks: Experimental Example 15) is very smooth. However, as shown in FIG. The surface of the particles after the milling process (Experimental Example 16) has irregularities, and it can be confirmed that the entire surface is subjected to strong processing by the mechanical milling process.

(Test Example 14)
The cross section of the intermediate particles obtained in Experimental Examples 15 and 16 was observed with SEM. After embedding the intermediate particles obtained in Experimental Examples 15 and 16 in a resin, the resin was polished with water-resistant paper or the like to obtain a cross section of the intermediate particles.
FIG. 28 is a diagram showing the cross-sectional observation result of the intermediate particle according to Test Example 14, where (a) is the observation result of the entire cross-section of the intermediate particle obtained in Experimental Example 15, and (b) is the Experimental Example 16. The observation result of the whole cross section of the obtained intermediate particle, (c) is an enlarged observation result of the surface portion of (b).

  As shown in FIG. 28 (a), the one not subjected to the mechanical milling process (processing time 0 ks: Experimental Example 15) has a circular shape with a smooth surface shape.

Looking at FIG. 28 (b), the one after the mechanical milling process (Experimental Example 16) shows a deformation in the surface shape as compared with the one not subjected to the mechanical milling process. It can be confirmed that the surface is strongly processed.
As shown in FIG. 28 (c), after the mechanical milling process, the center part has a needle-like structure, and in the range from about 20 to 40 μm in the depth direction from the surface, It can be confirmed that different microstructures appear uniformly on the surface side.
In FIG. 28 (c), the cross-sectional hardness of the portion appearing on the surface side as a fine structure different from the central portion was measured to be 397 HV, and the cross-sectional hardness of the central portion was measured to be 369 HV. It was.

  Since the Ti-6Al-4V alloy is an HCP phase that is a stable phase at room temperature, in FIG. 28C, a fine structure different from the central part appearing on the surface side, and a needle-like structure in the central part It is inferred that both are HCP phases.

(Experimental example 17)
The intermediate particles obtained in Experimental Example 15 were sintered under a predetermined temperature condition and pressure condition in an argon atmosphere, and a disc-shaped sintered body (metal) having a thickness of 2.5 to 5.5 mm and a diameter of 15 mm. Material).
The mold and apparatus used for sintering are the same as in Experimental Example 5.

  FIG. 29 is a diagram illustrating temperature conditions and pressure conditions according to Experimental Example 17. As shown in the figure, the temperature condition is that the temperature is raised at a rate of temperature increase of 1.67 K / s and held so that the holding temperature T is 1173 K and the holding time H is 5.4 ks. The temperature was set to cool down at s. Further, the pressure condition is increased so that the holding pressure P becomes 200 MPa when reaching 1173 K under the above temperature condition, and is maintained at 200 MPa during the holding time H, and then the pressure reduction rate is 1.7 MPa / s. It was set to step down.

(Experiment 18)
Using the intermediate particles obtained in Experimental Example 16, the same operation as in Experimental Example 17 was performed to obtain a disk-shaped sintered body (Experimental Example 18).

(Test Example 15)
The metal materials obtained in Experimental Examples 17 and 18 were cut to obtain test pieces, and the crystal grains in each metal material were observed using an EBSD detector provided in the SEM.

  FIG. 30 is a diagram showing a crystal grain boundary map in each metal material according to Test Example 15, where (a) is a crystal grain boundary map of the metal material obtained in Experimental Example 17, and (b) is Experimental Example 18. It is a crystal grain boundary map of the metal material obtained by (1). In the figure, the scale bar indicates 20 μm.

As shown in FIG. 30 (a), the cross-sectional structure of the sintered product (Experimental Example 17) that has been sintered without performing the mechanical milling process is constituted by a relatively coarse acicular crystal structure. The fine crystal grain seen in is not seen.
Thus, the metal material which concerns on the experiment example 17 sintered without performing a mechanical milling process does not have the fine grain structure area | region made into the network structure.

As shown in FIG. 30 (b), the cross-sectional structure of the sintered product after the mechanical milling process (Experimental Example 18) includes a fine grain structure region composed of fine crystal grains, and has a needle-like shape. A plurality of coarse grain structure regions constituted by coarse crystal grains are included.
It can be seen that the plurality of coarse grain structure regions are dispersed in the fine grain structure region, and the fine grain structure region has a network structure.
In Experimental Example 18, the cross-sectional area ratio of the fine grain structure region was 57%.
In Experimental Example 18, the average crystal grain size of the fine crystal grains constituting the fine grain structure region was 3.7 μm.

As described above, the Ti-6Al-4V alloy used in Experimental Example 18 starts solid phase transformation from an HCP phase that is a stable phase at room temperature to a BCC phase that is a metastable phase at room temperature at about 1200 K. .
Therefore, when sintering is performed under the temperature condition shown in FIG. 29, the temperature is raised so as to pass the transformation start temperature at which transformation from the HCP phase to the BCC phase occurs. As a result, BCC phase crystal grains are deposited in a fine grain structure region composed of HCP phase crystal grains. Thereby, the fine grain structure region becomes a metal structure composed of finer crystal grains.

  As a result, as shown in FIG. 30 (b), the average crystal grain size of the fine crystal grains constituting the fine grain structure region is 3.7 μm as described above. The coarsening of the fine crystal grains is suppressed.

(Test Example 16)
Using a universal testing machine, each of the metal materials obtained in Experimental Examples 17 and 18 was subjected to a tensile test until breaking.

  FIG. 31 is a diagram showing the relationship between the tensile strength obtained by the tensile test in Test Example 16 and the elongation at break.

In the figure, the metal material sintered without mechanical milling (Experimental Example 17) had a tensile strength of 934 MPa and an elongation at break of 18.7%.
On the other hand, the metal material (Experimental Example 18) sintered after performing the mechanical milling process for 90 ks has a tensile strength of 1043 MPa, which is higher than that of Experimental Example 17. The elongation at break is 22.6%, which is also higher than that of Experimental Example 17.

  In this way, by conducting a mechanical milling process on the powder particles and sintering, the metal structure is composed of a fine-grain structure region of a network structure and a coarse-grain structure region arranged inside the network. It can be confirmed that the metal materials according to 17 and 18 can maintain the ductility while increasing the strength as compared with the metal material of Experimental Example 12 which does not have the fine grain region of the network structure.

[Regarding the region of fine grain structure]
Below, the result of having further verified about the detail of the fine grain structure area | region is demonstrated.
(Test Example 17)
About the metal-material test piece by Experimental Example 6 obtained in Test Example 3, the phase distribution in the cross section of the test piece was observed using an EBSD detector.

  FIG. 32 is a diagram showing the observation results of Test Example 17, where (a) is a crystal grain boundary map of the metal material obtained in Experimental Example 6, and (b) is the phase distribution of the same part as (a). FIG. In FIG. 32B, the light gray area indicates the FCC phase and the dark gray area indicates the HCP phase. In the figure, the scale bar indicates 100 μm.

  As shown in FIGS. 32 (a) and 32 (b), the coarse crystal grains constituting the coarse grain structure region are FCC phases, and a fine HCP phase is seen at the grain boundary between the coarse crystal grains. It can be seen that the coarse grain structure region is almost composed of the FCC phase.

On the other hand, it can be confirmed that the fine grain structure region has a two-phase structure including the FCC phase and the HCP phase. That is, the fine crystal grains constituting the fine grain structure region include two types of crystal grains (FCC phase crystal grains and HCP phase crystal grains) having different crystal structures. This result is consistent with the result of the X-ray diffraction pattern of the test piece of Experimental Example 6 in Test Example 7.
Most of the HCP phase crystal grains in the fine grain structure region are as fine as several μm, and relatively large grains as small as 10 μm are also seen.

Moreover, when the cross-sectional area ratio of the HCP phase in Experimental Example 6 was determined, it was 23.0%.
In the result of Test Example 4, the cross-sectional area ratio of the fine grain structure region of Experimental Example 6 was 57.3%, so that the crystal grain of the HCP phase was 40.3% with respect to the cross-sectional area ratio of the fine grain structure region. It can be confirmed that it is contained at a rate of 1%.

(Experimental example 19)
Using the intermediate particles obtained in Experimental Example 2, the same operation as in Experimental Example 5 was performed except for the temperature drop rate condition included in the temperature condition, to obtain a disk-shaped sintered body (metal material). The cooling rate is 17.1 K / s (set as a control program setting value with a cooling time of 60 s) and Experimental Examples 5 to 8 (1.1 K / s: set as a control program setting value with a cooling time of 900 s) The temperature was cooled and cooled at a faster rate than that.

(Test Example 18)
An X-ray diffractometer was used for each of the metal material (Experimental Example 6) obtained under the condition of a relatively low temperature drop rate (Experimental Example 6) and the metal material obtained under the condition of a relatively fast temperature drop rate (Experimental Example 19). The diffraction pattern was measured.
FIG. 33 is a diagram showing an X-ray diffraction pattern according to Test Example 18. In the upper part, the X-ray diffraction pattern of Experimental Example 19 is shown in the upper part, and the X-ray diffraction pattern of Experimental Example 6 is shown in the lower part.

  Referring to FIG. 33, in any of Experimental Example 6 and Experimental Example 19, the peak of the FCC phase and the peak of the HCP phase can be seen.

Here, paying attention to the peak intensity of the (111) plane of the FCC phase and the peak intensity of the (10-11) plane of the HCP phase, the peak intensity of the (111) plane of the FCC phase in Experimental Example 19 is very large. Appears. On the other hand, the peak intensity of the (10-11) plane of the HCP phase appears very small.
Therefore, the relative peak intensity of the (10-11) plane of the HCP phase with respect to the peak intensity of the (111) plane of the FCC phase in Experimental Example 19 is a very small value.
On the other hand, the relative peak intensity of the (10-11) plane of the HCP phase with respect to the peak intensity of the (111) plane of the FCC phase in Experimental Example 6 is not as small as that of Experimental Example 19.
It can be seen that the relative peak intensity of the (10-11) plane of the HCP phase in Experimental Example 19 is very small compared to the relative peak intensity of the (10-11) plane of the HCP phase in Experimental Example 6. .

  From this result, it can be seen that the amount of the HCP phase contained in the metal material obtained in Experimental Example 19 is relatively smaller than that of the metal material obtained in Experimental Example 6. The cross-sectional area ratio of the HCP phase in the metal material obtained in Experimental Example 6 is 23.0%, and the amount of the HCP phase contained in the metal material obtained in Experimental Example 19 is a value sufficiently smaller than this value. I know that there is.

Moreover, it turns out that precipitation of a HCP phase is suppressed by temperature-falling rapidly to normal temperature from the FCC phase single phase area | region by setting a temperature-fall rate high from the said result.
Thus, it is clear that the amount of the HCP phase of the obtained metal material can be adjusted by adjusting the temperature drop rate conditions during sintering.

(Test Example 19)
A tensile test was performed on the metal materials obtained in Experimental Examples 6 and 19 using a universal testing machine. Test equipment, test conditions, and the like are the same as in Test Example 6.

34 is a stress-strain curve obtained by the tensile test according to Test Example 19. FIG.
In the figure, the metal material (Experimental Example 6) obtained under the condition of a relatively slow temperature drop rate had a tensile strength of 1283 MPa and an elongation at break of 24.3% (same as Experimental Example 6 of Test Example 6). is there).

  On the other hand, in the metal material (Experimental Example 19) obtained under the condition where the temperature decrease rate is relatively high, the tensile strength is 1031 and the elongation at break is 17.5%, both the tensile strength and the elongation at break are reduced.

  Thus, the metal material according to Experimental Example 6 in which the fine grain structure region of the network structure is a two-phase structure of the HCP phase and the FCC phase is compared with the metal material according to Experimental Example 19 in which the amount of HCP phase is sufficiently small. Thus, it can be confirmed that the strength and ductility can be increased.

DESCRIPTION OF SYMBOLS 1 Fine grain structure area | region 1a Fine crystal grain 1a1 1st crystal grain 1a2 2nd crystal grain 2 Coarse grain structure area 2a Coarse crystal grain 3 Powder particle 8 Surface part fine grain structure area 8a Surface part fine crystal grain

Claims (13)

A metallic material consisting essentially of a single metal or alloy,
The metal structure of the metal material is
A fine grain structure region composed of fine crystal grains;
A plurality of coarse grain structure regions constituted by coarse crystal grains having an average crystal grain size larger than the average crystal grain size of the fine crystal grains,
The fine grain structure region is a network structure in which the plurality of coarse grain structure regions are dispersed in the fine grain structure region,
The fine crystal grain is a metal material having a two-phase structure by including two kinds of crystal grains having different crystal structures.   The metal material according to claim 1, wherein the crystal structure of one of the two types of crystal grains is a hexagonal close-packed structure.   3. The metal material according to claim 2, wherein crystal grains having a hexagonal close-packed structure are included at a ratio of 40% or more with respect to a cross-sectional area ratio of the fine grain structure region.   The metal material according to claim 1, wherein a ratio of the fine grain structure region is 20% or more and 70% or less in terms of a cross-sectional area ratio.   The metal material according to claim 1, wherein an average crystal grain size of the fine crystal grains is 5 μm or less.   The metal material according to claim 1, wherein the metal material is formed by sintering powder particles substantially consisting of a single metal or alloy.   The metal material according to claim 1, wherein the single metal or alloy is at least one selected from a Co—Cr—Mo alloy, an austenitic stainless steel, and a manganese steel. A method for producing a metal material obtained by sintering powder particles substantially consisting of a single metal or alloy,
(A) forming on the surface of the powder particles a surface portion fine grain structure region constituted by fine crystal grains having an average crystal grain size smaller than an average crystal grain size of crystal grains constituting the powder particle; An intermediate particle having a coarse-grained region having a surface-fine-grained region on the surface and a coarse-grained region having an average grain size larger than the average grain size of the fine-grained particles in the center. And obtaining
(B) By sintering the intermediate particles, the surface portion fine grain structure regions of each intermediate particle are bonded to each other, and the metal structure is bonded to each other, and the surface portion fine particle structure regions are bonded to each other. A metal material including a fine-grained texture region and a plurality of the coarse-grained texture regions included in the intermediate particles, wherein the coarse-grained texture regions are the fine-grained texture regions. Forming a metal material disposed inside the mesh, and
In the step (B), other solid phase crystal grains different from the solid phase of the fine crystal grains constituting the fine grain structure region before the temperature rise due to the temperature rise when sintering the intermediate particles Is a method for producing a metal material that precipitates in the metal structure.   The method for producing a metal material according to claim 8, wherein in the step (A), the surface fine particle structure region is formed on the surface of the powder particle by subjecting the powder particle to strong processing.   The method for producing a metal material according to claim 9, wherein the strong processing is mechanical milling. In the step (A), a portion of the metastable phase existing on the surface of the powder particle is transformed into a stable phase by the strong processing, so that the surface of the powder particle is substantially a single phase of the stable phase. The surface portion fine grain structure region is formed,
In the step (B), the other solid phase is a metastable phase,
The method for producing a metal material according to claim 9 or 10, wherein a crystal grain of a metastable phase is precipitated in the fine grain structure region by increasing a temperature when sintering the intermediate particles.   In the step (B), the temperature of the single metal or alloy is increased so as to pass a temperature at which solid phase transformation starts, so that the crystal grains of the other solid phase are precipitated. The manufacturing method of the metal material as described in any one.   The single metal or alloy is at least one selected from a Co-Cr-Mo alloy, an austenitic stainless steel, a Ti-Al-V alloy, a Ni-Ti alloy, and a manganese steel. Metal material manufacturing method.