WO2007114439A1

WO2007114439A1 - Material having superfine granular tissue and method for production thereof

Info

Publication number: WO2007114439A1
Application number: PCT/JP2007/057478
Authority: WO
Inventors: Hiromi Miura
Original assignee: National University Corporation The University Of Electro-Communications
Priority date: 2006-04-03
Filing date: 2007-04-03
Publication date: 2007-10-11
Also published as: US20090165903A1; JPWO2007114439A1

Abstract

Disclosed is a method for production of a material having a superfine granular tissue. The method comprises the steps of: providing a metal or alloy having a stacking fault energy of 50 mJ/mm2 or less; and processing the metal or alloy so as to introduce a deformed bicrystal having an interbicrystalline spacing of 200 nm or shorter into the tissue of the metal or alloy. The method enables to provide a material having a superfine granular tissue, wherein the material is characterized by containing a bicrystal in the crystalline tissue and having an interbicrystalline spacing in the bicrystal of 200 nm or shorter.

Description

Material having ultrafine grain structure and method for producing the same

Technical field

[0001] The present invention relates to a material having an ultrafine grain structure and a method for producing the same.

Background art

[0002] As a method for increasing the mechanical strength of a metal material or an alloy material, a method for refining crystal grains in a material structure is known. Crystal grain refinement also has another advantage of improved material processability. Therefore, various studies on crystal grain refinement have been conducted. The most common grain refinement method is a so-called thermomechanical treatment method. In this method, crystal grains are refined by heat-treating the processed material under various conditions. For example, a method of refining crystal grains by recrystallizing a hot-rolled copper alloy at a temperature of about 300 ° C to 400 ° C has been proposed (Patent Document Do, A method has been proposed in which a ferrous metal after rolling or cold rolling is annealed at a temperature of about 750 ° C. to refine crystal grains (Patent Document 2). The crystal grain size obtained by this method is at least about 1 μm.

[0003] In recent years, attention has been focused on a crystal grain ultra-miniaturization technique called an ultra-strong processing method.

Typical examples of ultra-strong processing methods are ECAP (Equal Channel Angular Press) method and ARB (Accumulate Roll Bonding method).

[0004] The ECAP method is a method in which a metal material called a billet is inserted into an L-shaped mold and extruded from the opening, and the crystal grains are made ultrafine without changing the shape. (For example, Non-Patent Document 1). On the other hand, the ARB method is a method in which the plate material is rolled to about 50%, cut in half, two cut plates are stacked, and this is rolled again several times. Through a series of treatments, the crystal grains of the material can be made ultrafine. (For example, Non-Patent Document 2).

Patent Document 1: International Publication No. 2004Z022805 Pamphlet

Patent Document 2: Japanese Patent Laid-Open No. 62-182219

Non-patent literature 1: RZ Valiev, Islamic Galiev (RK Islamgaliev), Alexa Ndrov (IV Alexandrov), Material Science (Mat. Sci.), 45 卷, 2000, p.103 Non-Patent Document 2: Shin Yabu, Iron and Steel, 2002, 88 卷, p.359-369

Disclosure of the invention

Problems to be solved by the invention

[0005] However, the ECAP method described above is not suitable for industrial ultrafine grain processing because it requires a large number of processing steps and cannot produce a long material. In the ARB method described above, in the thickness direction, crystal grains with a grain size of about 0.1 μm can be obtained. In the force rolling surface, the crystal grains become coarse and uniform in the in-plane direction. It is not possible to obtain an equiaxed ultrafine grained structure. Therefore, there may arise a problem that the strength distribution of the material becomes non-uniform or the material does not have a desired strength. This method is also not suitable for industrial mass production with many processing steps. For this reason, there is a need for a crystal grain refinement technology that can form an equiaxed and uniform ultrafine grain structure more easily and increase the material strength.

[0006] The present invention has been made in view of such problems, and provides a material having a high-strength ultrafine grain structure and a method capable of easily manufacturing such a material. It is an issue to provide.

Means for solving the problem

[0007] In the present invention, a material having an ultrafine grain structure having a stacking fault energy of 50 mjZmm ² or less and also having a metal or alloy force, the crystal structure includes twins, and the twin spacing in the twins is A material characterized by being 200 or less is provided. By making the material structure into such an ultrafine grain structure, the maximum strength of the material can be improved.

[0008] Here, it should be noted that the term "twin" in the present application is a concept including a deformation twin.

[0009] Further, in the present invention, a material having an ultrafine grain structure made of a metal or an alloy having a stacking fault energy of 50 mjZmm ² or less and having a crystal grain size of 20ηπ A material characterized by having recrystallized grains in the range of ~ 600 nm is provided. By setting the material structure to such a characteristic recrystallized structure, a material having high strength and uniform ultrafine crystal grains can be obtained. [0010] Further, in the present invention, there is provided a method for producing a material having an ultrafine grain structure, the step of providing a metal or alloy having a stacking fault energy of 50 mjZmm ² or less, and processing the metal or alloy. And introducing a deformation twin having a twin spacing of 200 nm or less into the metal or alloy structure.

[0011] In the method of the present invention, it is possible to introduce a large number of deformation twins into the material structure. By utilizing the crossing of these deformation twins, the crystal grains are made ultrafine. be able to.

Here, the step of introducing the deformation twin may include a step of subjecting the metal or the alloy to a multiaxial forging process (hereinafter also referred to as “MDF processing”) at a temperature of room temperature or lower. Good! This method is characterized in that the processing process is simple and a material having an ultrafine grain structure can be provided by a simple processing step.

[0013] In particular, said step of multi-axis forging process, 1 X 10- ⁴ Z seconds or strain rate, good have a step of forging the metal or alloy!ヽ. MDF processing at a high strain rate can increase the deformation resistance of the material, making it easier to introduce deformation twins into the material.

[0014] Alternatively or separately, the temperature below room temperature is preferably an absolute temperature of 223 K or less. In such an MDF cache treatment at a very low temperature, the deformation resistance of the work material can be easily increased, so that the same effect as when the strain rate is increased can be obtained more easily. it can. Therefore, a material having an ultrafine grain structure can be provided more easily.

[0015] Further, after the forging process, there may be a step of annealing the metal or alloy that has been subjected to the multi-axis forging process. Thereby, the material structure after forging can be made homogeneous.

[0016] As another method, the step of introducing the deformation twin may include a step of rolling the metal or alloy at a temperature of room temperature or lower. In this method, it is possible to introduce high-density deformation twins into the material structure relatively easily as soon as cutting stress is applied to the material. Therefore, when this method is applied, the crystal grains can be made ultrafine more easily than the MDF processing method described above. [0017] Further, after the rolling treatment, a step of annealing the rolled metal or alloy may be added. Thereby, the material structure after rolling can be homogenized.

[0018] The step of annealing after forging or rolling is performed by annealing the metal or alloy at a temperature of 0.5 X Tm or less, where Tm is the melting point of the metal or alloy. Prefer to have a step ヽ. By performing the annealing treatment at such a temperature, it becomes possible to make the structure uniform without coarsening the ultrafine grains obtained after forging or rolling.

[0019] Further, the step of rolling may include the step of rolling the metal or alloy at a rolling speed of 5 X 10-mZ seconds or more. Since the deformation resistance can be increased by increasing the rolling speed, a large number of deformation twins can be introduced into the material structure.

[0020] Further, the step of rolling may include a step of rolling the metal or alloy so that a final reduction ratio is 20% or more. Since the deformation resistance can be increased by increasing the rolling reduction, a large number of deformation twins can be introduced into the material structure.

[0021] In particular, it is preferable that the rolling step includes a step of rolling the metal or alloy at an absolute temperature of 223K or lower. By performing the rolling process at such an extremely low temperature, the deformation resistance of the material can be increased. Therefore, a large number of deformation twins can be introduced without increasing the rolling speed and Z or the rolling reduction during rolling, and a material having an ultrafine grain structure can be provided more easily.

[0022] In the present invention, the first packet includes a layered twin group substantially oriented in the first direction, and at least one of the twins in the first packet includes: A second packet comprising a layered twin group substantially oriented in a second direction, wherein the first direction and the second direction include those forming an angle other than 60 degrees. A material having an ultrafine grain structure is provided. Here, “packet” means a layered twin group oriented in the same crystal orientation as described later.

[0023] Further, according to the present invention, there is provided a first yarn and weaving including a first packet including a plurality of layered twin groups oriented substantially in the first direction in one crystal grain. , In the first packet At least one of the twins has a first structure having a second packet comprising a twin group oriented in a second direction substantially different from the first direction; and the first packet And a third structure containing recrystallized grains formed of a plurality of layered twins oriented in substantially the same direction. A material having an ultrafine grain structure is provided.

[0024] The material having such an ultrafine grain structure may be brass.

The invention's effect

In the present invention, a high-strength material having an ultrafine grain structure is provided. In addition, a material having such an ultrafine grain structure can be obtained relatively easily.

Brief Description of Drawings

FIG. 1 is a diagram schematically showing an example of a structure diagram of a material having an ultrafine grain structure of the present invention.

FIG. 2 is a schematic explanatory diagram of an MDF cache processing method.

FIG. 3 is a stress strain curve of a copper 30 mass% zinc material manufactured by the ultrafine grain processing method (MDF processing method) of the present invention.

[Figure 4] TEM photograph showing the structure of copper 30mass% zinc alloy sample after MDF processing at 77K (a) and 300K (b), and a schematic diagram showing the enlarged packet part of the photograph in (b) (C).

[FIG. 5] A structure chart (OIM map) of a copper 30 mass% zinc alloy sample after annealing at 503 K for 8 hours after cryogenic rolling treatment using an orientation dispersion analyzer.

FIG. 6 is a diagram schematically showing an example of an apparatus configuration for carrying out the ultrafine grain processing method of the present invention.

Is [7] Temperature 77K, MDF mosquito卩E processed copper 30 mass% zinc alloy of TEM observation organization in the true strain rate 1 X 10- ³ Z seconds.

[Fig. 8] A graph showing changes in the Vickers hardness of a material when 60% of a copper 30mass% zinc alloy is rolled at 77K and then annealed at temperatures of 503K, 523mm and 543mm.

[Fig. 9] A structural photograph of a copper 30mass% zinc alloy rolled 60% at 77% and annealed at 523K for 1000 seconds. (B) is an enlarged view of (a). FIG. 10 is a graph showing the relationship between the annealing time and the average grain size in the material structure when 60% of a 30 mass% zinc alloy is rolled at 77K and then annealed at both temperatures of 503K and 523K.

FIG. 11 is a diagram showing a stress-strain curve at room temperature of pure copper after performing MDF cache treatment at a cryogenic temperature of 77K and room temperature (300K).

Explanation of symbols

[0027] 10 apparatus

20 Rolling roller

30 Transfer platform

40 materials

50 Cryogenic bath

100 Ultrafine grain structure

110 Twin

120 knots

BEST MODE FOR CARRYING OUT THE INVENTION

[0028] In the present invention, a step of providing a metal or alloy having a stacking fault energy of 50 mjZmm ² or less, a step of introducing a deformation twin having a twin spacing of 200 nm or less in the structure of the metal or alloy, A material having an ultrafine grain structure is produced by a method characterized by comprising:

In the present application, the “ultrafine grain structure” means a structure having an “average crystal grain size” force of less than 1 μm. Here, the average crystal grain size is measured for the deformed structure from the transmission electron microscope (TEM) photograph using the linear crossing method, and for the annealed structure, the orientation dispersion analyzer (Orientation Imaging MicroscopyZOIM) ) In the crystal orientation distribution image obtained by the analysis, the structure having a boundary with an orientation difference of 3 degrees or more is taken as the crystal grain and calculated from the average grain area.

Conventionally, twins are considered not to contribute to the mechanical strength of materials, and it is considered important to exclude twins from crystal yarns and weaves in order to improve the mechanical strength of materials. It was done. However, in the present invention, on the contrary, this twin is actively introduced into the material structure, It is characterized in that the grains are made finer, thereby improving the material strength. More specifically, in the present invention, a large number of deformation twins are introduced into the material structure by performing processing with large deformation on the workpiece material, and these deformation twins The crystal grains are made ultrafine by cutting. According to the study of the present inventor, by such processing

In particular, the mechanical strength of the material is remarkably improved when an ultrafine grain structure having a twinning force of deformation twins of not more than 00 is obtained.

Here, the “twin spacing” is included in the distance D of the arrow, that is, in one twin 110 in the ultrafine grain structure 100 having a plurality of twins 110 as shown in FIG. The interval between twin lines and the twin lines adjacent to them. In addition, since such twin spacing cannot be measured with a normal optical microscope, in the present application, from a structural photograph obtained by observation at about 8000 to 80000 times with a transmission electron microscope, The twin spacing of twins contained in the ultrafine grain structure is measured.

[0032] The processing method for introducing a large number of such deformation twins into the material is not particularly limited, and various methods can be used.

[0033] For example, as a processing method for introducing a large number of deformation twins, there is an MDF (Multi-direction al forging) processing method. This method is also called a multi-axis forging method, and is a processing method that repeats compression by changing the forging direction of the work material so that the major axis direction becomes the compression direction for each forging process in one direction.

A specific example of the MDF processing method will be described below with reference to FIG. Figure 2 is a schematic illustration of the MDF processing method. First, a bulk material with a rectangular aspect ratio as shown in Fig. 2 (1) is prepared. The aspect ratio of the bulk material is determined by the compression ratio by forging from each axial direction shown in (2) to (4) (each forging is called a pass). In other words, the aspect ratio of the bulk material can be changed according to the compression rate for each pass to be adopted. In the example in the figure, this corresponds to a case where the processing strain for one pass is 0.4. When one processing strain is increased, deformation resistance increases, and deformation twins are more likely to appear. For example, if the strain that can be introduced into the material in one pass is 0.8 (in that case, the aspect ratio is 1.0: 1.49: 2.22), theoretically, the total strain should be 2.4 This means that 3 pass processing is required. [0035] By such an MDF cache treatment, a large number of deformation twins can be introduced into the material. Further, the crystal grains are refined by the crossing of the introduced deformation twins. In particular, in MDF caloche processing, multi-directional force materials are compressed, so that an equiaxed ultrafine grain structure can be obtained after processing. Furthermore, this processing method can form a superfine grain structure in a material by a simple processing process of changing the compression axis and repeating forging, so mass production of a material with an ultrafine grain structure is easy. There is a feature that can be.

[0036] In general, in order to introduce a large number of deformation twins into a material structure at once, it is desirable to apply deformation to the material while the resistance to deformation of the material (hereinafter referred to as deformation resistance) is large. . Therefore, in order to increase the deformation resistance, it is preferable that the temperature of the material during processing is as low as possible, and the strain that can be applied to the material at one time is as large as possible.

[0037] From such a viewpoint, when the MDF processing method is adopted as a processing method for introducing the deformation twins, it is preferable that the MDF processing is performed at a temperature of room temperature (300K) or less. As a result, the deformation resistance during processing can be further increased, and more deformation twins can be introduced at one time. Further, when the MDF mosquitoes卩E processed in under "cryogenic" below 223 K (absolute temperature), the processing speed is selected so the strain rate of about 1 X 10- ⁴ Z seconds or more, Otherwise, it is preferable to select as the strain rate of about 5 X 10- ⁴ Z seconds. If a large strain rate is selected, the amount of deformation applied to the material for each pass can be increased, and the deformation resistance can be increased, so that the processing temperature is high (about room temperature). However, more deformation twins can be introduced into the material structure.

[0038] In addition, when industrially mass-producing a material having an ultrafine grain structure by the MDF cache processing method, the major axis direction of the work material becomes the compression direction for each processing. In addition, it is preferable to automatically rotate the work material. Such an operation can be easily performed by using, for example, an electric or mechanical work material position (or direction) control means such as a manipulator. This eliminates the hassle of changing the orientation of the material to be coated for each pass.

Through such a process, for example, a material having an ultrafine grain structure 100 composed of a large number of twins 110 as schematically shown in FIG. 1 can be obtained. In the example of this figure, The average grain size is at most in the range of about 500 nm to less than 1 μm, and the twin spacing is about 80 to 10 Onm.

[0040] Such deformed twins tend to appear parallel to one direction within one grain, but when the sample is changed in the direction of addition and forged again, deformed twins in another direction appear, and both As deformed twins cut into each other, they change into ultrafine crystal grains. In the deformation twin, the two crystals sandwiching the twin plane have an orientation difference of about 60 degrees, and due to the appearance of the deformation twin, the formation of the deformation twin itself, as well as the crossing and cutting of them. An ultrafine grain structure surrounded by high misorientation grain boundaries is easily generated.

[0041] It should be noted that the forged material may be annealed!ヽ. By performing the annealing treatment, it is possible to homogenize the ultrafine grain structure including a large number of deformation twins generated by deformation. The annealing treatment is preferably performed at the lowest possible temperature. This is because if the processing temperature is increased, the growth of ultrafine crystal grains may be promoted. In particular, when the melting point of the forging material is Tm (K), the annealing temperature is preferably 0.5 Tm or less. For example, in the case of a copper-one 30 mass% zinc alloy, the melting point of this alloy is 1223K, so the processing temperature is 611K or less.

FIG. 3 shows an example of a stress strain curve at room temperature of a material having an ultrafine grain structure manufactured by the method of the present invention. These test samples were produced by introducing strains of 0.4 (1 pass), 2.4 (6 passes) and 6.0 (15 passes) into a copper 30 mass% zinc alloy by the MDF processing described above. is there. The upper figure shows the result of the sample manufactured by MDF force treatment at 77K, and the lower figure shows the result of the sample manufactured by MDF processing at room temperature (300K). Show me! The maximum strength of this material, which has not been subjected to normal grain refinement, is about 500 MPa. On the other hand, the maximum strength of the sample processed at MDF at 77K increased from 600MPa to 900MPa, and the introduced strain was 0.4 (1 pass) in the sample processed at MDF at 300K. Except for the sample, the maximum intensity increases from 700 MPa to 800 MPa!

FIG. 4 shows a structure photograph of the sample after the MDF processing. This sample was manufactured by introducing strain of 6.0 (15 passes) into a copper-30mass% zinc alloy by the MDF caloe process described above. The photo (a) on the left shows the organization after the MDF cache treatment at 77K. The middle photo (b) is after the MDF cache processing at 300K. The right figure (c) shows an enlarged schematic view of a part of the central tissue photograph.

[0044] In particular, as shown in Fig. (C), layered twins oriented in the same crystal orientation are formed in the crystal grains of the sample after the MDF cache treatment. In the present application, such a layered twin group will be specifically referred to as “packet” (or packet 120). When the twins in the packet 120 are observed in more detail, a second packet having a smaller layered twin group is formed inside one twin. It can be seen that the twins included in the packet are oriented in the same crystal orientation. Such a structure is considered to be caused by repeating the deformation process by MDF processing, so that the twins in the packet 120 are divided into smaller twin groups. According to this consideration, twins included in a twin group constituting one packet are divided into finer layered twin groups each time a deformation process is applied, whereby further fine packets are separated. As it is formed, the crystal grains are refined and an ultrafine grain structure is formed.

In general, when a plurality of twin groups are introduced into the structure by a thermomechanical treatment or the like, the difference in orientation between the twin groups is 60 degrees. However, in the case of twins introduced by MDF processing, by repeating the deformation process, the packet existing before the deformation process is deformed, and the twins constituting the packet are crystal rotated. Occurs. Therefore, the orientation of the twin group forming the first packet generated by the first deformation process and the twin group formed in the twin of the second packet generated by the second deformation process. The difference will be at an angle other than 60 degrees.

[0046] As described above, by applying the method for producing a material having an ultrafine grain structure of the present invention to a material to be processed, it is possible to make the crystal grain ultrafine and to reduce the strength of the material. It becomes possible to improve.

[0047] Another processing method for introducing a large number of deformation twins is a rolling method. In order to introduce a large number of deformation twins in the material, it is preferable to shear the material. In the rolling method, shear stress is applied to the material, and a high-density deformation twin can be introduced into the material structure relatively easily. Therefore, when this method is applied, it is possible to make the crystal grains ultra finer more easily than the MDF processing method described above. . In addition, the rolling method can be applied to a large-scale material such as a large-area plate material that is less restricted by the shape of the material to be processed.

[0048] The processing conditions for rolling the material include "very low temperature processing", "low temperature high speed processing", "low temperature high pressure processing" or "high speed high pressure processing"! I prefer to use one or the other. Here, “cryogenic treatment” is a method of rolling in a state where the material to be rolled is kept at an “extremely low temperature” of 223 K (absolute temperature) or less. As described above, in order to introduce a large number of deformation twins into the structure at once, it is preferable to make the temperature of the material as low as possible and to increase the strain applied to the material as much as possible in order to increase the deformation resistance. . In “Cryogenic treatment”, the material temperature is lowered to a cryogenic temperature of 223K or lower, and the rolling treatment is performed. Therefore, the deformation resistance can be increased regardless of other processing condition parameters. That is, under these conditions, the deformation resistance state sufficient to form a large number of deformation twins can be obtained simply by maintaining the material at a very low temperature. The feature is that detailed control of other parameters is unnecessary.

[0049] "Low-temperature high-speed treatment" and "low-temperature high-pressure treatment" are methods in which rolling is performed while the material to be rolled is maintained at a temperature of about 223 to 300K (room temperature). Only by rolling at such a temperature, it is difficult to introduce high-density deformation twins as in the “cryogenic treatment”. Therefore, under these processing conditions, high-density deformation twins are introduced into the material to be rolled, in combination with parameters that increase the amount of deformation that can be applied to the material at one time. For example, in the case of “low temperature high speed processing”, a large amount of deformation twins is introduced into the material to be rolled by adding strain to the material to be rolled at a high speed in order to increase the deformation resistance. In order to apply strain to the material at a high speed, the rolling speed needs to be higher than that in the “cryogenic treatment”, and is preferably at least 5 × 10−mZ seconds. On the other hand, in the case of “low temperature and high pressure treatment”, the reduction rate of the material to be rolled is reduced by treating the material to be rolled under high pressure rolling conditions by taking advantage of the fact that deformation twins are more likely to be generated as the amount of strain increases. Introduce high-density, high-density deformation twins. In this case, the final reduction ratio of the material is preferably 20% or more. In addition, it is desirable that the final reduction ratio is 60% or more for the viewpoint power to uniformly disperse the deformation twins.

[0050] Further, "high-speed and high-pressure treatment" refers to a rolling treatment on a material to be rolled in a non-low temperature region such as room temperature. This is a method of increasing the deformation resistance of the material to be rolled and introducing high-density deformation twins by combining high-speed processing and high-pressure processing. For example, in the case of general rolling at room temperature, deformed twins appear when the rolling speed is 5 × 10-mZ seconds or more and the rolling reduction is 70% or more.

[0051] Of these rolling treatment methods, "cryogenic treatment" is particularly preferred! In other methods, it is necessary to apply a large strain or pressure to the material at once, which causes problems that the equipment becomes special and large, and cannot be processed with standard equipment. Also, depending on the material, such as a highly ductile material, it may be difficult to apply a large strain at a time. However, if there are no restrictions on equipment or materials, it will be apparent that deformation twins may be introduced under the above processing conditions.

[0052] The above-mentioned rolled material may be annealed. By performing the annealing treatment, it is possible to homogenize the ultrafine grain structure including a large number of deformation twins generated by deformation. The annealing treatment is preferably performed at the lowest possible temperature. This is because if the processing temperature is increased, the growth of ultrafine grains may be promoted. In particular, when the melting point of the rolled material is Tm (K), the annealing temperature is preferably 0.5 Tm or less. For example, in the case of a copper-one 30 mass% zinc alloy, the melting point of this alloy is 1223K, so the processing temperature is 611K or less.

[0053] By such annealing treatment, for example, as shown in FIG. An almost uniform ultrafine grain structure of about 600 nm can be obtained. Here, Fig. 5 is a map using an orientation dispersion analyzer (OIM) of a sample that was subjected to a cryogenic rolling process at 77K (rolling rate: 60%) and annealed for 8 hours at a temperature of 503K. . In this figure, it should be noted that the ultrafine grain structure produced by the method of the present invention does not progress so much even after annealing as will be described later. This is thought to be because a large number of deformation twins with different orientations contained in the structure play a role of restraining the crystal grains and suppress the grain growth. Therefore, the material having the ultrafine grain structure obtained by the method of the present invention has a significant characteristic if it is excellent in thermal stability.

[0054] According to the research results of the present inventors, the twin spacing as shown in FIG. An ultrafine grain structure containing a large number of deformation twins tends to be obtained more easily with a metal or alloy having a lower stacking fault energy. This is because, for metals or alloys with large stacking fault energy, even if processing such as MDF cache treatment is performed, the dislocation density accumulated in the material is difficult to increase, and the critical stress for generating deformation twins is applied to the material. This is because it is difficult to apply more stress. Therefore, the present invention is preferably applied to a metal or alloy having a stacking fault energy of 50 mj / mm ² or less. Here, examples of metals or alloys with low stacking fault energy include silver (stacking fault energy of about 22 mjZmm ² ), copper (78 mjZmm ² ), cobalt (15 mjZmm ² ), nickel (128 mj / mm ² ), brass. (About 20mj / mm ² ) and stainless steel (211mjZmm ² ). Here, brass means an alloy of copper and zinc and contains 20 mass% or more of zinc (the aforementioned stacking fault energy is the value of copper 30 mass% zinc alloy). Even when the stacking fault energy of the metal or alloy itself exceeds 50 mj / mm ² , stacking fault energy is remarkably increased by adding one or more impurity elements to such metal or alloy. It is known that it can be reduced. For example, when 9% silicon is added to copper, the stacking fault energy decreases to 5 mj / mm ² . Therefore, it should be noted that the above-described stacking fault energy can be included in the scope of the present invention by adding an impurity element even in a metal or alloy or other alloy having 50 mjZmm ² or more.

[0055] Hereinafter, an example of a method for producing a material having an ultrafine grain structure according to the present invention will be described with reference to the drawings. In the following example, as a processing method for introducing deformation twins into the material structure, a method using a rolling process under the “cryogenic treatment” condition! I will explain in a moment.

[0056] Fig. 6 schematically shows an example of a rolling apparatus for carrying out the method of the present invention (rolling treatment under cryogenic treatment conditions). In the method of the present invention, the rolling device 10 includes a cryogenic bath 50, a transport device 30, and a rolling roll 20. The conveying device 30 is used to guide the material 40 to be rolled toward the rolling tool 20. The cryogenic bath 50 is used to cool the material to be rolled 40 in advance. The temperature of the cryogenic bath 50 is 223 K or less, but is particularly preferably a liquid nitrogen temperature (77 K) or less. Here, in another rolling apparatus 10, the position of the cryogenic bath 50 may be changed or deleted. What is important is that the material to be rolled 40 is cooled to the above-mentioned temperature immediately before the material to be rolled 40 passes through the rolling roll 20. The For example, a cooling tank is provided in the middle of the conveyance path, the material to be rolled 40 passes through the cooling tank before being conveyed to the rolling roll 20, and the rolling portion of the material to be rolled 40 is cooled to the temperature as described above. It is okay to configure the device as described.

[0057] The rolling apparatus 10 can introduce deformation twins into the material to be rolled 40 such as a copper 30 mass% zinc alloy by the following operation. First, the material 40 to be rolled that has been pre-cooled in the cryogenic bath 50 is placed on the conveying device 30. Next, the conveying device 30 is operated, and the material 40 to be rolled moves in the direction of the rolling roll 20. When the material to be rolled 40 is conveyed to the position of the rolling roll 20, it is rolled by the rolling roll 20 here. The feed speed (rolling speed) of the material to be rolled 40 is preferably about 1 × 10−mZ seconds or more, but is not particularly limited thereto. In addition, the rolling reduction of one pass is preferably about 10 to 20%. The force is not particularly limited to this. This is because, as described above, in the case of the cryogenic treatment condition, the influence of the reduction rate and the feed rate itself on the generation density of deformation twins is not significant.

[0058] Such an operation is repeated as many times as necessary (pass), and a large number of deformation twins are introduced into the material. It is preferable that the material to be rolled 40 be recooled every time one pass of the rolling process of the material to be rolled 40 is completed. Prevents the temperature of the material to be rolled 40 from being raised by the rolling process, and the temperature of the material to be rolled 40 cannot be maintained in the extremely low temperature range suitable for deformation twinning when the material to be rolled 40 is re-rolled. It is to do. However, if the temperature of the material 40 to be rolled is maintained in an appropriate cryogenic temperature range after one pass rolling (for example, when the entire rolling processing apparatus 10 is installed in a low temperature environment), the material to be rolled It is also possible to repeatedly perform rolling of 2 to several passes in a range where the temperature of 40 does not exceed a predetermined value.

[0059] In the rolling method using such an apparatus, the material to be rolled 40 is kept at a very low temperature and the deformation resistance is sufficiently high, so that a large number of deformation twins can be easily introduced. Further, after the treatment, a material having an ultrafine grain structure can be obtained.

[0060] On the other hand, it is possible to introduce deformation twins into the material 40 to be rolled even at a non-cryogenic temperature such as room temperature (high-speed and high-pressure treatment). In this case, there is an advantage that the cryogenic bath 50 of the above-described apparatus is not necessary. However, it is necessary to improve the deformation resistance by increasing the feed speed of the material 40 to be rolled or by increasing the rolling reduction ratio during rolling. Example For example, in the high-speed and high-pressure treatment, the feed speed of the material to be rolled is 5 × 10−mZ seconds or more, and the final rolling reduction after rolling is 70% or more. Even with such a rolling process, an ultrafine grain structure having uniform and high-density deformation twins can be obtained.

[0061] Annealing treatment may be performed using the material rolled in this manner! As described above, the annealing treatment is preferably performed at the lowest possible temperature. For example, when the melting point of the material is Tm, an ultrafine grain structure having recrystallized grains having a crystal grain size in the range of 20 nm 600 can be obtained by annealing at a temperature of 0.5 X Tm or less.

[0062] Hereinafter, various evaluation test results of materials having an ultrafine grain structure obtained by applying the method of the present invention will be described.

(Experiment 1)

In Experiment 1, MDF processing was performed using the test material, and the strength of the obtained material was evaluated. As the material for Experiment 1, a 30 mass% copper alloy with a stacking fault energy of 20 mj / mm ² was used.

[0063] Figure 7 shows the temperature 77K, the TEM observation tissue copper 30mas s% zinc alloy after the MDF processed in the true strain rate 1 X 10- ³ Zeta seconds. In this process, the number of passes of the MDF cache process that covers the material is six, and the cumulative strain introduced into the material is 2.4. From this figure, many deformation twins are introduced into the material by MDF processing, and an ultrafine grain structure with an average crystal grain size of 1 μm or less is formed by the cross-cutting of these deformation twins. You can see that In addition, the halo ring (a phenomenon in which diffraction spots are connected and appear in a ring shape) appears in the 1 / zm region limited field diffraction image circled in the figure. Usually, halo ring is caused by the close proximity of diffraction spots corresponding to each particle when there are many crystals with different orientations in the structure. Therefore, it can be seen from this result that the material structure obtained by this method contains a large number of ultrafine crystal grains.

[0064] Fig. 3 shows the stress-strain curve at room temperature of the specimen obtained by MDF processing at temperatures of 77K and 300K (room temperature). In this test piece, the amount of strain introduced into the material was changed to 0.4 2.4 and 6.0 by changing the number of passes of the MDF Karoe treatment to the material to 1, 6, and 15, respectively. Yes. For specimens obtained by 77K cryogenic MDF cache treatment, the strain force increased from .4 to 6.0 as shown in the upper part of the figure. Then, the maximum strength changed to 600MPa force 900MPa. Elongation was about 20% in all specimens. The maximum strength of the same material obtained by conventional thermomechanical processing is usually around 500 MPa. Therefore, this result shows that the strength of the material is remarkably improved by applying the MDF processing method. In addition, the elongation of the same material obtained by conventional ultrafine grain processing methods such as ECAP is usually about 10%. Therefore, it can be seen that the elongation can be improved by applying the ultrafine grain processing method of the present invention. On the other hand, in the case of a test piece obtained by MDF cache treatment at 300 K (room temperature), As shown, the maximum strength changed from 500 MPa to 800 MPa when the strain increased from 0.4 to 6.0. In this way, even in 300K room temperature MDF processing, there was a tendency for strength to increase with increasing strain. However, the strength improvement effect was small compared to the cryogenic treatment at 77K. This is because the MDF processing at room temperature makes it more difficult to increase the deformation resistance of the material compared to the cryogenic treatment at 77K, and it is included in the structure when compared with the same number of paths. This is probably because the number of deformation twins is smaller. However, as a result of TEM observation, a sample (maximum strength, about 800MPa) treated with MDF cache up to a cumulative strain of 6.0 formed uniform ultrafine crystal grains even at room temperature. It was recognized that In addition, the three specimens manufactured under these treatment conditions had an elongation of about 20%, which is an improvement over the conventional material (10%).

(Experiment 2)

In Experiment 2, the same material (copper-30ma _SS % zinc alloy) as in Experiment 1 was used, and the cryogenic rolling process was performed, and the state of the resulting structure and its stability were evaluated. First, using this material, a cryogenic rolling process was performed using the apparatus shown in FIG. The material temperature during rolling was 77K. The rolling reduction for each pass during rolling was in the range of 10% force and 20%. The structure of the material after 60% rolling was observed with a transmission electron microscope (TEM). As a result, it was found that a very fine grain structure with a grain strength of about 500 nm to less than l μm was developed, similar to the structure shown in Fig. 1. In addition, a large number of deformation twins are included in the crystal grains, and it was found that the twin spacing in these deformation twins is about 80 to 100 nm. [0066] Next, a change in structure was examined when a material rolled 60% at 77K was annealed at various temperatures. FIG. 8 is a graph showing changes in the Vickers hardness of the material when the material is rolled at 77K by 60% and then annealed at temperatures of 503K, 523%, and 543%. From this figure, it can be seen that although it depends on the annealing temperature, the hardness decreases rapidly after 10 ³ 10 ⁴ seconds, and static recrystallization occurs after this time.

[0067] Fig. 9 shows a TEM photograph of a sample that was annealed for 1000 seconds at a temperature of 523K after a 30 mass% copper alloy was cryogenically rolled at 77% (rolling rate 60%). The photo on the right is a high magnification view of the photo on the left. From these photographs, at the stage of annealing at 523K for 1000 seconds, the “packets” generated by the deformation process still remain! However, some “packets” have been recrystallized and static recrystallization has occurred. I found out that has started. Furthermore, it was found that recrystallized grains formed of a plurality of layered twins with uniform orientation were formed in part of the crystal grains. Since the recrystallized grains have a grain size of about 20 nm, the twins contained in the recrystallized grains are considered to have a grain size much smaller than 20.

[0068] In this way, by the cryogenic rolling treatment of copper 30mass% zinc alloy and the subsequent annealing treatment, "packets", recrystallized grains of this packet, and a plurality of layered twins with the same orientation are formed. An ultrafine grain structure was formed including the other recrystallized grains.

[0069] FIG. 10 shows the relationship between the annealing time and the average crystal grain size in the material structure when the material was rolled 60% at 77K and then annealed at both temperatures of 503K and 523K. The average crystal grain size in the data shown in parentheses in the figure (annealing time = 100 seconds) was difficult to distinguish because the grains were too fine, so the distance and length of the deformation twins (D and Calculated as a simple average of L). In other data, the average crystal grain size was calculated by the straight line crossing method using a transmission electron microscope as a crystal grain with a boundary structure. Thus, the reason why the structure having the boundary is the crystal grain is that the deformation twin contained in the structure has a high orientation difference of 60 degrees or more, and therefore, these structures are surrounded by the high orientation boundary. This is because it is obvious that it is a crystal grain. The fine deformation twins developed inside the crystal grains are not used in the calculation, and the actual crystal grain size is even smaller than the value shown in FIG. It can be seen from Fig. 10 that the crystal grains are not coarsened even by the annealing treatment and are about 0.6 / zm at the maximum. Fig. 5 shows an example of the structure when 60% of a 30mass% copper alloy is rolled at 77K and then annealed at 503K for 8 hours. This observation was performed using an orientation variance analyzer (OIM). From Fig. 5, it can be seen that the annealing process yielded almost uniform ultrafine crystal grains with an average grain size of about 500 nm. The average crystal grain size was calculated by taking the structure having a boundary with an orientation difference of 3 degrees or more as a crystal grain, but almost all the structures had a boundary with a high orientation difference of 15 degrees or more. Met. It can also be seen from the figure that the crystal grains are not coarsened even after a long annealing time of 8 hours. From this result, it is possible to obtain a uniform ultrafine grain structure by annealing the structure obtained by introducing a large amount of deformation twins, and further, the structure formed in this way. It was proved that is extremely stable thermally and difficult to coarsen. This is because, in the present invention, a large number of deformation twins are introduced into the material structure to make the crystal grains ultrafine, and the presence of a large number of twins with different orientations suppresses the grain growth. This is probably because of this.

(Experiment 3)

Next, for comparison, the same experiment was performed using pure copper (stacking fault energy 78mjZmm ² ). Figure 11 shows the stress-strain curve of pure copper at room temperature after the MDF cache treatment at 77K cryogenic temperature and room temperature (300K). The horizontal axis is cumulative strain. In the case of pure copper subjected to MDF processing at 300K, if the cumulative strain exceeds 2%, the maximum stress becomes 380 MPa, and the maximum stress does not change even after ultra-strong stress treatment up to cumulative strain 6 is performed. I got it. In addition, as a result of observation of the structure of the sample after the test, almost no deformation twins occurred. On the other hand, in the specimen subjected to MDF cache treatment at a temperature of 77 K, the maximum stress was 590 MPa at a cumulative strain of 2. When the microstructure of the specimen with strain up to cumulative strain 2 was observed, it was found that some deformation twins were partially formed. However, deformation twins were generated non-uniformly, and it was impossible to obtain a uniform ultra-fine grain structure on the entire surface, such as the aforementioned copper 30 mass% zinc alloy. This result shows that even if the deformation stress is large, it is difficult to obtain a deformation twin when the stacking fault energy of the material is large. This is because the material has an inherent critical stress to generate deformation twins with high probability, that is, the material is processed to generate a large number of deformation twins in the material structure. This indicates that the stress applied to the material must exceed the critical stress ( In the case of copper, critical stress is expected to be around 400 to 600 MPa). And with pure copper, which has a high stacking fault energy, the dislocation density is unlikely to increase. Therefore, even when processing such as MDF processing, the stress applied to the material cannot easily exceed this critical stress. Under the conditions, it is expected that a large number of deformation twins such as the copper 30mass% zinc alloy will not occur. This application claims priority based on Japanese patent applications 2006-102216 and 2006-120942 filed on April 3, 2006 and April 25, 2006. The contents are incorporated herein by reference.

Claims

The scope of the claims

[1] A material having an ultrafine grain structure with a stacking fault energy of 50 mjZmm ² or less and also having a metal or alloy strength,

A material characterized by containing twins in the crystal structure and having a twin spacing force in the twins of ¾00 or less.

[2] A material having an ultrafine grain structure with a stacking fault energy of 50 mjZmm ² or less and also having a metal or alloy power,

A material characterized by having recrystallized grains having a crystal grain size ranging from 20 to 600.

[3] A method for producing a material having an ultrafine grain structure,

Providing a metal or alloy having a stacking fault energy of 50 mjZmm ² or less; and processing the metal or alloy to introduce a deformation twin having a twin spacing of 200 or less in the structure of the metal or alloy. Steps,

A method characterized by comprising:

4. The method according to claim 3, wherein the step of introducing the deformation twin includes a step of subjecting the metal or alloy to a multiaxial forging process at a temperature of room temperature or lower.

[5] said step of multi-axis forging process, in 1 X 10- ⁴ Z seconds or strain rate method of claim 4 wherein the metal or is characterized by having a step of forging the alloy .

[6] The method according to claim 4, wherein the temperature below room temperature is an absolute temperature of 223K or less.

7. The method according to claim 4, further comprising a step of annealing the metal or alloy that has been subjected to multi-axis forging.

[8] The method according to claim 3, wherein the step of introducing the deformation twin includes a step of rolling the metal or alloy at a temperature of room temperature or lower.

9. The method according to claim 8, further comprising a step of annealing the rolled metal or alloy.

[10] The step of annealing, comprising the step of annealing the metal or alloy at a temperature of 0.5 XTm or less, where Tm is the melting point of the metal or alloy. 9. The method according to 9.

[11] The method according to claim 8, wherein the step of rolling includes the step of rolling the metal or alloy at a rolling speed of 5 × 10—mZ seconds or more.

[12] The method according to claim 8, wherein the step of rolling includes the step of rolling the metal or alloy so that the final reduction ratio is 20% or more.

13. The method according to claim 8, wherein the step of rolling includes the step of rolling the metal or alloy at a temperature of 223 K or less.

[14] having a first packet comprising a layered twin group substantially oriented in a first direction;

At least one of the twins in the first packet has a second packet of layered twin group forces substantially oriented in the second direction;

A material having an ultrafine grain structure characterized in that the first direction and the second direction include those having an angle other than 60 degrees.

[15] a first structure comprising a first packet comprising a plurality of layered twins substantially oriented in a first direction, wherein at least one of the twins in the first packet A first structure having a second packet comprising a twin group oriented in a second direction substantially different from the first direction;

A second structure comprising recrystallized grains of the first packet;

A third structure comprising recrystallized grains formed of a plurality of layered twins oriented in substantially the same direction;

A material having an ultrafine grain structure characterized by comprising:

[16] The material having an ultrafine grain structure according to [14] or [15], wherein the material is brass.