JP2023020858A - Titanium alloy production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a titanium alloy production method allowing easy control of the amount of oxygen contained in a titanium alloy.

SOLUTION: A titanium alloy production method at least comprises: a mixing step of obtaining a mixed powder by mixing a titanium powder, whose main component is titanium (Ti), and a Va group powder, whose main component is vanadium-group elements; a solidification step of obtaining a solidified body by heating and solid phase diffusion bonding of the mixed powder mixed in the mixing step; and a melting step of heating and melting the solidified body to generate a titanium alloy. In the solidification step, the solid phase diffusion bonding of the mixed powder is performed by heating and compression. In the melting step, the solidified body is melted by the vacuum arc remelting or cold crucible induction melting.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present invention relates to a method for producing titanium alloys.

Conventionally, as a method for producing a titanium alloy, for example, columnar titanium and a wire-shaped or thin-plate-shaped additive metal are set in a crucible of a levitation melting apparatus, melted under predetermined melting conditions, and naturally melted in the crucible. There is a technique in which a titanium alloy is obtained by cooling (see, for example, Patent Document 1). Further, as a method for producing a titanium alloy, for example, a titanium alloy is obtained by mixing titanium powder and vanadium group element powder, setting them in a heating container, and sintering them by pressurizing and heating them. There was (for example, see Patent Document 2).

Japanese Patent Application Laid-Open No. 2002-012923 Japanese Patent No. 3375083

By the way, in titanium alloys, it is generally considered preferable to reduce the content of oxygen, which is an unavoidable impurity, as much as possible. However, when it is intended to positively contain oxygen in a titanium alloy, the titanium alloy manufacturing method of Patent Document 1 described above mixes elements in the atmosphere into the titanium alloy during melting. It is difficult to control with high precision. As a result, in the production method of Patent Document 1, there was a problem that the amount of oxygen could not be controlled in the first place.

Further, according to the studies of the present inventors, the method for producing a titanium alloy of Patent Document 2 has a problem that titanium and vanadium group elements diffuse non-uniformly in the titanium alloy after sintering. As a result, the manufacturing method of Patent Document 2 has a problem that the oxygen contained in the oxide film of the titanium powder also diffuses unevenly.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing a titanium alloy that can homogenize the whole while controlling the composition ratio of the titanium alloy with high accuracy.

A method for producing a titanium alloy according to the present invention includes at least a mixing step of obtaining a mixed powder by mixing a titanium powder containing titanium (Ti) as a main component and a group Va powder containing a vanadium group element as a main component; A solidification step of heating the mixed powder mixed in the mixing step to cause solid phase diffusion bonding to obtain a solidified body, and a melting step of heating and melting the solidified body to produce a titanium alloy. Characterized by

In the solidifying step, the mixed powder is solid phase diffusion bonded by heating at any temperature between 900 and 1400.degree.

In the method for producing a titanium alloy according to the present invention, the solidification step is characterized in that the mixed powder is placed under a vacuum, and the mixed powder is solid-phase diffusion-bonded by heating and pressurizing.

The method for producing a titanium alloy according to the present invention is characterized in that, in the melting step, the solidified matter is melted by a vacuum arc remelting method or a cold crucible induction melting method.

The method for producing a titanium alloy according to the present invention is characterized in that the titanium alloy contains 0.4 to 1.7 at % of oxygen (O) when the total is 100 atomic % (at %).

The method for producing a titanium alloy according to the present invention is characterized in that the group Va powder contains tantalum (Ta) or niobium (Nb) as a main component.

The method for producing a titanium alloy according to the present invention is characterized in that the titanium alloy contains 1 to 8 at % of tin (Sn) when the total is 100 atomic % (at %).

The method for producing a titanium alloy of the present invention further comprises a heat treatment step of heat-treating the titanium alloy produced in the melting step, an aging treatment step of aging the heat-treated titanium alloy, wherein the titanium alloy that has undergone the melting step contains 15 to 27 at% tantalum (Ta), 1 to 8 at% tin (Sn), and 0 .4 to 1.7 atomic percent of oxygen (O), the balance being titanium (Ti) and unavoidable impurities, and in the aging treatment step, the titanium alloy is aged for 24 hours or less. , characterized in that an α phase is precipitated in the titanium alloy.

According to the method for producing a titanium alloy of the present invention, it is possible to obtain an excellent effect that each component of the titanium alloy can be homogenized while controlling the composition ratio contained in the titanium alloy with high accuracy.

1 is a flow chart showing the flow of a method for producing a titanium alloy according to an embodiment of the present invention; (A) is a schematic diagram of a HIP apparatus used in a method for producing a titanium alloy according to an embodiment of the present invention. (B) is a schematic diagram of an apparatus for performing a vacuum arc remelting method (VAR) used in a method for producing a titanium alloy according to an embodiment of the present invention; (A) is a photograph of an SEM image of a solidified body produced by HIP treatment, observed with a scanning electron microscope (SEM) at a magnification of 400 times. (B) is a photograph of an SEM image when elemental analysis of Ti was performed using X-rays in the range of (A). (C) is a photograph of an SEM image when elemental analysis of Ta was performed using X-rays in the range of (A). (D) is a photograph of an SEM image when elemental analysis of Sn was performed using X-rays in the range of (A). (A) shows the surface of a comparative titanium alloy (Ti-23.4Ta-3.4Sn-0.26O), which is a comparative example, observed at a magnification of 2000 using a transmission electron microscope (TEM). It is a photograph of a TEM image. (B) is a photograph of a TEM image when the surface of the first titanium alloy (Ti-23.4Ta-3.4Sn-0.75O) was observed using a transmission electron microscope (TEM) at a magnification of 2000. is. (C) is a photograph of a TEM image when the surface of the second titanium alloy (Ti-23.4Ta-3.4Sn-0.92O) was observed using a transmission electron microscope (TEM) at a magnification of 2000. is. The numerical values attached to the elements of Ta, Sn, and O in parentheses corresponding to the comparative titanium alloys and the first and second titanium alloys are those of the comparative titanium alloys and the first and second titanium alloys, respectively. represents the numerical value of atomic % (at %) of each element (Ta, Sn, O) when the whole is 100 atomic % (at %). 2 is a Ta—Ti binary phase diagram. FIG. When the total is 100 atomic % (at %), a titanium alloy (Ti-23Ta -xSn-0.26O) is a graph showing the results of a cold workability evaluation test. When the total is 100 atomic % (at %), a titanium alloy (Ti -23.4Ta-3.4Sn-xO) is a table showing the results of a cold workability evaluation test. (A) is a table showing the compositions of test pieces H1 and T1 produced using a titanium alloy according to an embodiment of the present invention. (B) is a stress-strain diagram showing the results of a tensile test on each of test pieces H1 and T1. (A) is a stress-strain diagram obtained as a result of a tensile test in which a test piece H1 was subjected to repeated stress-strain. (B) is a stress-strain diagram obtained as a result of a tensile test in which the test piece T1 was subjected to repeated stress-strain. (C) is a diagram in which the stress-strain diagrams of (A) and (B) are superimposed. (A) is a table showing compositions of test pieces H2 and T2 produced using a titanium alloy according to an embodiment of the present invention. (B) is a stress-strain diagram showing the results of a tensile test on each of test pieces H2 and T2. (A) is a stress-strain diagram obtained as a result of a tensile test in which stress-strain was repeatedly applied to the test piece H2. (B) is a stress-strain diagram obtained as a result of a tensile test in which the test piece T2 was subjected to repeated stress-strain. (C) is a diagram in which the stress-strain diagrams of (A) and (B) are superimposed. (A) is a drawing in which stress-strain diagrams, which are the results of tensile tests on test pieces T1 and T2, are superimposed. (B) is a diagram in which stress-strain diagrams obtained as a result of performing a tensile test in which stress-strain was repeatedly applied to each of the test piece T1 and the test piece T2 are superimposed. (A) is a table showing compositions of test pieces H3, T3, and T4 produced using a titanium alloy according to an embodiment of the present invention. (B) is a graph showing the results of a Vickers hardness test on each of a plurality of test pieces H3, T3, T4 with different heat treatment temperatures.

Hereinafter, a method for producing a titanium alloy according to embodiments of the present invention will be described with reference to the accompanying drawings. A method for producing a titanium alloy according to an embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG.

<Mixing process>
First, as shown in FIG. 1, Ti powder containing titanium (Ti) as the main component, Ta powder containing tantalum (Ta) as the main component, and Sn powder containing tin (Sn) as the main component were prepared. , and a mixing step of mixing them at a predetermined mixing ratio (step S100). In the present embodiment, Ti powder, Ta group powder, and Sn powder are all sieved with a sieve having a mesh size of 325 (mesh: mesh/inch) or less, and can pass through the sieve. It is assumed that the particle size (particle diameter) is large. The Ti powder preferably contains 90% or more of titanium (Ti), more preferably contains 95% or more of titanium (Ti), and further preferably contains 99% or more of titanium (Ti). . In this case, the remaining components of the Ti powder include components other than titanium (Ti). Further, the titanium (Ti) in the Ti powder may include pure titanium (Ti) or may include titanium (Ti) having an oxide film. The Ta powder preferably contains 90% or more of tantalum (Ta), more preferably 95% or more of tantalum (Ta), and even more preferably 99% or more of tantalum (Ta). In this case, the remaining components of the Ta powder include components other than tantalum (Ta). Moreover, the tantalum (Ta) in the Ta powder may include pure tantalum (Ta), or may include tantalum (Ta) having an oxide film. The Sn powder preferably contains 90% or more of tin (Sn), more preferably 95% or more of tin (Sn), and even more preferably 99% or more of tin (Sn). In this case, the remaining components of the Sn powder include components other than tin (Sn). Further, the tin (Sn) in the Sn powder may include pure tin (Sn) or tin (Sn) having an oxide film.

For the same weight, a powder with a smaller particle size will have more grains that make up the powder than a powder with a larger particle size. As a result, a powder with a smaller particle size has a larger surface area that reacts to oxygen than a powder with a larger particle size when compared at the same weight. Titanium powder (Ti) and tantalum powder (Ta) are in a stable state in the atmosphere due to an oxide film. As a result, when comparing at the same weight, mixing titanium powder (Ti) and tantalum powder (Ta) with a small particle size increases the O content in the final product titanium alloy than powder with a large particle size. Therefore, the particle size of titanium powder (Ti) and tantalum powder (Ta) affects the content of O in the titanium alloy, and the content of O in the titanium alloy should be determined by appropriately selecting the particle size of each powder. can be adjusted by Therefore, in order to provide a plurality of titanium alloys having different oxygen contents, the grain size of at least one of the Ti powder and the Ta powder should be changed. In addition, if the desired oxygen content cannot be achieved only by reducing the particle size of the Ti powder and/or Ta powder, the titania powder itself contains oxygen. You can mix.

For example, when the total is 100 atomic % (at %), 15 to 27 atomic % tantalum (Ta), 1 to 8 atomic % tin (Sn), and 0.4 to 1.7 atomic % oxygen (O ), Ti powder or titania powder, Ta powder, and Sn powder are uniformly mixed in a mixing ratio such that the balance consists of titanium (Ti) and unavoidable impurities. When the above is converted to weight %, Ta is 40 to 56 wt %, Sn is 2 to 10 wt %, and O is 0.1 to 0.1 wt % when the whole is 100 wt % (wt %). It becomes 3 wt% O, and the balance becomes titanium (Ti) and unavoidable impurities. For example, in the case of Ti-23.4Ta-3.4Sn-xO titanium alloy, when the whole is 100% by weight, Ta powder is 52% by weight, Sn powder is 5% by weight, and the rest is Ti powder or Mix to form titania powder. The O content is adjusted by adjusting the particle size of Ti powder or Ta powder having an oxide film on the surface, or by using titania powder. In addition, since the Sn powder content is small in the present embodiment, it is presumed that the Sn powder has little effect on the O content. In addition, the display of at % represents atomic %, and the display of at % below represents the atomic % of the corresponding element when the entire corresponding titanium alloy is 100 atomic % (at %). shall be used. In addition, hereinafter, the numerical values attached to the elements of Ta, Sn, and O representing the composition of the titanium alloy (see the parentheses immediately after the titanium alloy below) are 100 atomic % (at % ) represents the numerical value of atomic % (at %) of each element (Ta, Sn, O).

<Solidification process>
Next, as shown in FIG. 1, the mixed powder of Ti powder or titania powder, Ta powder, and Sn powder uniformly mixed in the mixing step (hereinafter simply referred to as mixed powder) is placed under vacuum, A solidification step is performed in which the mixed powder is solidified by solid-phase diffusion bonding (step S101). The mixed powder becomes a solidified body by the solidification step. In addition, since the mixed powder is solid-phase diffusion-bonded in a state of being placed under a vacuum, it is possible to restrict the intrusion of unexpected oxygen (O) from the outside air into the solidified body. Further, in the present embodiment, the term "solidified body" refers to a mass obtained by subjecting the mixed powder to solid-phase diffusion bonding. In addition, in the solidification step, for example, normal heat treatment (for example, sintering treatment by heating), pressure/heat treatment in which pressure and heat are applied at the same time, and the like are adopted. Examples of pressurization and heat treatment include hot isostatic pressing (HIP), spark isostatic pressing (SIP), and spark plasma sintering (SPS). Sintering) are used, and the mixed powder is solidified by either of them. Incidentally, HIP and SIP are isotropic (hydrostatic) pressurization, and SPS is directional pressurization (axial pressurization) because a press machine and a die are used. Further, in the present embodiment, the pressure under vacuum where the mixed powder is arranged is preferably 1.0×10 ⁻¹ (Pa) or less, and 1.0×10 ⁻² to 1.0×10 ⁻⁵ (Pa), more preferably 1.0×10 ⁻² to 1.0×10 ⁻³ (Pa).

Here, with reference to FIG. 2(A), the case of using a hot isostatic pressing method (hereinafter referred to as HIP treatment) in the solidification process will be described as an example. First, the HIP container 2 is filled with the mixed powder 5 under pressure. The HIP container 2 is composed of, for example, a cylindrical container with one end face open and the other end face closed, and a lid. The mixed powder 5 is filled into a cylindrical container while being compressed, and the cylindrical container is placed in a vacuum chamber of an electron beam device (not shown). Then, the pressure in the vacuum chamber is set to a vacuum state within a range of, for example, 1.0×10 ⁻² to 1.0×10 ⁻³ (Pa), and electron beam welding is performed to the opening of the HIP container 2. The lid is welded to seal the HIP container 2 . As a result, the mixed powder is placed under vacuum in the HIP container 2 .

Although it is preferable to use a material other than Ta as the material for the HIP container 2, Ta is extremely expensive and not realistic for mass production. For this reason, for example, as the material of the HIP container 2, it is preferable to use a material containing Ti or iron as a main component, and more preferably a material containing iron as a main component. Incidentally, in a general HIP process, the HIP container 2 is made of the same material as the material with the highest melting point (here, Ta) in the mixed powder 5 .

Then, the HIP container 2 is installed inside the heat insulating part 3A of the HIP furnace 3 of the HIP apparatus 1 . The HIP apparatus 1 is configured so that the inner region of the heat insulating portion 3A of the HIP furnace 3 can be brought into a high-temperature, high-pressure atmosphere by heating with a substantially inert gas such as argon and the heater 4. FIG. Also, the gas is supplied to the inside of the HIP furnace 3 from the outside through the gas introduction passage 3B of the HIP furnace 3 . When high temperature and high pressure are applied to the HIP container 2 for a predetermined time, the mixed powder 5 is pressurized and heated through the HIP container 2 . As a result, the mixed powder 5 is solidified by solid-phase diffusion bonding. In addition, since the mixed powder 5 is sealed in the HIP container 2 in a vacuum state, even if the mixed powder 5 is pressurized and heated through the HIP container 2, unexpected oxygen (O) is added to the solidified body from the outside air. entry can be restricted. Incidentally, immediately after the HIP treatment, the HIP container 2 and the solidified body are in a state of being strongly bonded. Therefore, in order to separate the HIP container 2 and the solidified material, the HIP container 2 and the layer in which the HIP container 2 and the solidified material are mixed are cut by a machine tool. As a result, only the solidified body remains. Thereby, a cylindrical solidified body is formed.

In the HIP process, the temperature inside the HIP furnace 3 of the HIP apparatus is set to, for example, 1000° C., the pressure is set to 98 MPa, and the HIP container is placed under these conditions for about a predetermined time to form a solidified body. Note that the temperature inside the HIP furnace 3 may be any range as long as the HIP container 2 is not damaged or melted. The temperature inside the HIP furnace 3 is, for example, preferably 700.degree. C. to 1600.degree. C., more preferably 900.degree. C. to 1400.degree. Also, the pressure inside the HIP furnace 3 is preferably 50 to 200 (MPa), more preferably 70 to 180 (MPa), and even more preferably 90 to 120 (MPa).

Note that the melting point of Ta is 3017° C., which is a fairly high temperature. Even if the internal temperature of the HIP furnace 3 is, for example, about 900° C. to 1400° C., in the case of a high Ta content ratio of 15 at % or more like the titanium alloy of the present embodiment, each powder is completely uniform. less likely to spread to That is, the solidified body produced by the HIP treatment may not uniformly diffuse Ta, Sn, Ti and O, and may include a region where any one of Ta, Sn, Ti and O is unevenly distributed. . In order to confirm this, the inventor of the present application set the internal temperature of the HIP furnace 3 to 1000° C. and the internal pressure of the HIP furnace 3 to 98 MPa. , the content of Sn powder is 3.4 at%, the rest is Ti powder, and the particle size of each powder is 10 to 45 μm). It was investigated how Ta, Sn, and Ti are distributed in. The results are shown in FIGS. 3(A) to 3(D). FIG. 3(A) is a photograph of an SEM image when the solidified body is observed at a magnification of 400 using a scanning electron microscope (SEM). As shown in FIGS. 3B to 3D, the distribution of Ti, Ta, and Sn in the range of the SEM image of FIG. It can be seen that the Sn powder is not uniformly dispersed. From the above, when the internal temperature of the HIP furnace 3 is about 900° C. to 1400° C., the Ti powder, Ta powder, and Sn powder are completely alloyed by diffusing each other in this composition with a very high Ta ratio. It was actually confirmed that the probability is low.

On the other hand, if the internal temperature of the HIP furnace 3 is made higher than the above temperature, damage to the HIP container 2 itself is caused, and failure of the HIP furnace 3 itself is likely to occur. Also, in order to realize heating at a temperature higher than 1400° C., it is conceivable to form the HIP container 2 from a material (for example, Ta) that can withstand high temperatures. If Ta material is used, it will be extremely expensive, so it is not realistic.

<Dissolution process>
Next, as shown in FIG. 1, a dissolving step of dissolving the solidified mixed powder solidified in the solidifying step is performed (step S102). The solidified body is melted by the melting process to form a titanium alloy ingot. As described above, in the solidified body, each component is not uniformly dispersed, but by performing the melting process, each component is uniformly melted (dissolved), and a titanium alloy ingot in which each component is uniformly dispersed is obtained. Obtainable. In the melting step, in order to simultaneously melt Ta, Sn, and Ti having different melting points and diffuse them uniformly, it is preferable to melt the solidified body at a temperature at which all of Ta, Sn, and Ti can be simultaneously melted. . In the melting process, for example, a vacuum arc remelting method (VAR: Vacuum Arc Remelting), an electroslag remelting method (ESR: ElectroSlag Remelting), a vacuum induction melting method (VIM: Vacuum Induction Melting), a cold crucible induction melting method (CCIM Cold Crucible Induction Melting), Plasma Arc Melting (PAM), or Electron Beam Melting (EBM) is used, and the solidified body is melted by any of them.

Here, with reference to FIG. 2(B), a case where the vacuum arc remelting method (VAR) is used in the melting process will be described as an example. First, the cylindrical solidified body provided in the solidification process is used as the consumable electrode 6 and connected to the rod 9 suspended in the arc melting furnace 8 . As a result, the consumable electrode 6 is suspended from the rod 9 in the arc melting furnace 8 with the molten metal pool 10 positioned directly below. In this state, when an electric current is passed through the consumable electrode 6 via the rod 9, an arc discharge occurs between the consumable electrode 6 and the molten metal pool 10. The high heat generated by the arc discharge heats and melts the consumable electrode 6, which pools underneath to form an ingot 11 of titanium alloy.

After connecting the ingot 11 of the titanium alloy as the consumable electrode 6 to the rod 9, the ingot may be placed in the arc melting furnace 8 as described above and melted again by applying an electric current. This treatment can be repeated more than once, since the reliability of homogenization of each component can be improved by performing this treatment a plurality of times. A titanium alloy is provided as described above.

<Cold working process>
Next, as shown in FIG. 1, cold working is performed on the titanium alloy ingot provided in the melting step (step S103). Cold working of a titanium alloy ingot forms a titanium alloy workpiece such as a wire or bar.

<Heat treatment process>
Next, as shown in FIG. 1, a heat treatment step is performed to heat-treat the titanium alloy workpiece provided in the cold working step (step S104). The heat treatment temperature is, for example, preferably 600°C to 1000°C, more preferably 700°C to 900°C.

<Aging treatment process>
Next, as shown in FIG. 1, an aging treatment step is performed for aging the titanium alloy heat-treated in the heat treatment step (step S105). The aging treatment temperature is preferably 200°C to 550°C, more preferably 300°C to 500°C. When the titanium alloy in the present embodiment is subjected to the aging treatment for a predetermined period of time, an equiaxed α phase or the like precipitates in the titanium alloy. The α-phase is not limited to equiaxed texture, and may include other forms.

4(B) and (C) show the first titanium alloy (Ti-23.4Ta-3.4Sn-0.75O) and the second titanium alloy (Ti-23.4Ta-3.4Sn- 0.92O) is observed with a transmission electron microscope (TEM) at a magnification of 2000 times. FIG. 4A shows a photograph of a TEM image of a comparative titanium alloy (Ti-23.4Ta-3.4Sn-0.26O) as a comparative example under the same conditions as above. The first and second titanium alloys and the comparative titanium alloys were heat treated at 890°C for 2 hours and then aged at 300°C for 2 hours.

In the photographs of TEM images of the first titanium alloy and the second titanium alloy shown in FIGS. 4(B) and (C), a white equiaxed α phase is precipitated. In the photograph shown in FIG. 4(C), in which the O content is high, more equiaxed α phases are precipitated than in the photograph shown in FIG. 4(B). On the other hand, in the photograph of the TEM image of the comparative titanium alloy shown in FIG. 4(A), the white equiaxed α phase is hardly precipitated. 4(B) and (C), the equiaxed α phase precipitates even after aging treatment for about 2 hours, but the O content as shown in FIG. 4(A) It was confirmed that the equiaxed α-phase was not precipitated in the case of low modulus by aging treatment for about 2 hours. From this result, it was confirmed that the precipitation amount of the equiaxed α phase in the titanium alloy can be controlled by the O content and the aging treatment time. The content of O when the entire titanium alloy is 100 at% is preferably 0.4 at% or more, more preferably 0.6 at% or more, and most preferably 0.75 at% or more. I understand.

By the way, as a result of analyzing the photographs of the TEM images shown in FIGS. 4(B) and (C), the average grain size of the equiaxed α phase was 0.13 μm. Also, the average grain size of the equiaxed α phase in the second titanium alloy (Ti-23.4Ta-3.4Sn-0.92O) was 0.17 μm. From this result, it can be inferred that as the O content increases, the average grain size of the equiaxed α phase precipitated by the aging treatment tends to increase accordingly. In the titanium alloy of the present invention, the average grain size of the equiaxed α phase is preferably anywhere between 0.05 and 1.00 μm, and any between 0.05 and 0.50 μm. more preferably 0.05 to 0.30 μm.

In addition, as a result of analyzing the photograph of the TEM image of the first titanium alloy shown in FIG. 4(B), the area ratio of the equiaxed α phase was 1.89%. The area ratio of the equiaxed α phase in the second titanium alloy (Ti-23.4Ta-3.4Sn-0.92O) shown in FIG. 4(C) was 5.24%. The area ratio of the equiaxed α phase refers to the ratio of the area occupied by the equiaxed α phase per unit area in the photographs of the cross-sectional TEM images shown in FIGS. . From this result, it can be inferred that as the O content increases, the area occupation ratio of the equiaxed α phase precipitated by the aging treatment increases accordingly. In the titanium alloy of the present invention, the area occupancy of the equiaxed α phase is preferably between 0.1 and 20%, more preferably between 0.1 and 15%. is more preferred, more preferably anywhere between 0.1 and 10%.

As described above, even if the aging treatment time is the same, if the content of O in the titanium alloy is high, the amount of precipitation of the equiaxed α phase increases, and if the content of O in the titanium alloy is low, the precipitation of the equiaxed α phase increases. less quantity. Therefore, when a specific amount of equiaxed α phase is precipitated in a titanium alloy by aging treatment, a titanium alloy with a high O content requires a shorter aging treatment time than a titanium alloy with a low O content.

However, the equiaxed α phase increases the strength of the titanium alloy. However, when the content of O is too high, the solubility limit of O is exceeded, TiO and TiO ₂ are produced, and workability is lowered. This is shown in the cold workability evaluation test shown in FIG. 7, which will be described later.

Incidentally, a general titanium alloy also contains a small amount of oxygen as an unavoidable impurity. In that case, the content of O is 0.2 at % or less when the entire titanium alloy is 100 at %. In such a titanium alloy, Ta as a β-stable element functions more than O as an α-stable element, and even if aging treatment is performed, the equiaxed α phase does not precipitate easily, and the equiaxed α phase precipitates. requires aging treatment for several days. On the other hand, like the titanium alloy of the present embodiment, if the content of O is positively increased and the content of O reaches 0.4 at %, O functions as an α-stabilizing element, and 12 hours of A minimum amount of equiaxed α phase is precipitated by aging treatment, and a sufficient amount of equiaxed α phase is precipitated by aging treatment for 24 hours. Further, when the content of O in the titanium alloy reaches 1.7 at %, O functions sufficiently as an α-stabilizing element, and sufficient equiaxed α-phase is precipitated even with aging treatment for 1 hour. Therefore, the aging treatment time is preferably 1 to 24 hours, more preferably 1 to 4 hours.

<Structure of Titanium Alloy>
Next, an example of a titanium alloy produced by the method for producing a titanium alloy described above will be described. The titanium alloy in the embodiment of the present invention contains 15 to 27 at% tantalum (Ta), 1 to 8 at% tin (Sn), and 0.4 to It consists of 1.7 atomic % of oxygen (O) and the balance of titanium (Ti) and unavoidable impurities. Note that the content of titanium (Ti) in the balance is not particularly limited, and it is sufficient that titanium (Ti) is the most abundant element among the contained elements when considered in terms of atomic ratio.

Further, the titanium alloy includes an α-type titanium alloy having a hexagonal close-packed (HCP) α-phase as a parent phase, a β-type titanium alloy having a body-centered cubic (BCC) β-phase as a parent phase, a close-packed It is roughly classified into three types of α + β type titanium alloys in which the α phase, which is a hexagonal crystal (HCP), and the β phase, which is a body-centered cubic crystal (BCC) coexist, but the type of titanium alloy according to the present invention is particularly limited. not.

<Tantalum (Ta)>
Tantalum (Ta) causes the titanium alloy in the present embodiment to undergo thermoelastic martensite transformation. Ta has the function of lowering the transformation temperature from the β phase to the α phase, stabilizing the β phase at room temperature, and making slip deformation (plastic deformation) less likely to occur.

The content of Ta is preferably 15 to 27 at%, more preferably 19 to 25 at%, and 22 to 24 at% when the entire titanium alloy is 100 atomic% (at%). Most preferred.

The upper limit of the Ta content is set based on the melting point of the titanium alloy. FIG. 5 is a Ta—Ti binary phase diagram. As shown in FIG. 5, if the Ta content exceeds 27%, the melting point of the titanium alloy may be about 2000K or higher, requiring a special melting furnace and increasing the production cost. In addition, since the melting of the Ta raw material may be incomplete, the quality of the titanium alloy is deteriorated.

The lower limit of the Ta content is set based on the above-described β-phase stabilizing function and the mechanical properties of the titanium alloy as a material for medical devices, a biomaterial, and the like. That is, the β-phase stabilizing function decreases as the Ta content decreases, and when the Ta content is less than 15 at %, it becomes difficult to maintain the β-phase up to room temperature. Therefore, when the Ta content is less than 15 atomic %, even if tin (Sn) is added, the mechanical properties (Young's modulus, tensile strength, and elastic It becomes difficult to obtain deformation strain). Therefore, the Ta content is preferably 15 at % or more, more preferably 19 at % or more, and most preferably 22 at % or more when the entire titanium alloy is 100 at %.

<Tin (Sn)>
Tin (Sn) has an α-phase stabilizing function of increasing the transformation temperature and stabilizing the α-phase. In addition, Sn has the function of suppressing the precipitation of the ω phase, which is a factor that increases the Young's modulus, and enhancing the superelastic effect of the titanium alloy.

The Sn content is preferably 1 to 8 at %, more preferably 2 to 6 at %, when the entire titanium alloy is 100 atomic % (at %).

The upper limit of the Sn content is set based on the workability (cold workability) of the titanium alloy. 2 is a graph showing the results of a cold workability evaluation test for a titanium alloy (Ti-23Ta-xSn-0.26O) having a Ta content of 23 at % when the entire titanium alloy is 100 at %. Note that x is the Sn content (at %) when the entire titanium alloy is 100 at %. In this cold workability evaluation test, first, a plurality of test pieces with the Sn content x changed to 0 at%, 1.5 at%, 3 at%, 6 at% and 9 at% when the entire titanium alloy is 100 at%. (thickness: 1 mm, no heat treatment) was prepared. Then, these test pieces were cold-rolled to a thickness of 0.1 mm (reduction rate: 86%), and the number of cracks with a length of 1 mm or longer in each test piece after cold rolling was counted. The crack count was performed within a range of 140 mm in the rolling direction of each test piece.

As shown in FIG. 6, as a result of this evaluation test, it was confirmed that the occurrence of cracks of 1 mm or more abruptly increased when the Sn content was 9 at %, that is, the workability abruptly deteriorated. rice field. Moreover, even when the Ta content was different, the same tendency was shown. Therefore, the Sn content is preferably 8 at % or less, more preferably 6 at % or less, in order to obtain good workability when the entire titanium alloy is 100 at %.

The lower limit of the Sn content is not particularly limited, but in order to sufficiently exhibit the above-described ω-phase suppressing function, the Sn content is 1 at% or more when the entire titanium alloy is 100 at%. is preferred.

<Oxygen (O)>
Oxygen (O) has an α-phase stabilizing function of raising the transformation temperature and stabilizing the α-phase. O has a stronger α-phase stabilizing function than Sn. In addition, O has the function of restraining the deformation of the crystal and preventing the appearance of shape memory properties and softening.

The content of O is preferably 0.4 to 1.7 at %, more preferably 0.6 to 1.0 at %, when the entire titanium alloy is 100 atomic % (at %). The O content can be changed by changing the grain size of at least one of Ti powder and Ta powder. It is possible to change the O content by changing the grain size of the Sn powder. It is difficult to influence the rate.

<Regarding the upper limit of the content of O (evaluation of cold working)>
The upper limit of the O content is set based on the workability (cold workability) of the titanium alloy. If the content of O is too high, the titanium alloy becomes too hard due to the function of preventing softening of O, resulting in poor workability. FIG. 3 shows a titanium alloy (Ti-23.4Ta-3.4Sn-xO) with a Ta content of 23.4 at% and a Sn content of 3.4 at% when the entire titanium alloy is 100 at%. It is a table showing the results of a cold workability evaluation test for. Note that x is the content of O (at %) when the entire titanium alloy is 100 at %.

In this cold workability evaluation test, first, when the entire titanium alloy (Ti-23.4Ta-3.4Sn-xO) is 100 at%, the O content x is 0.26 at%, 0.59 at%, 0 A plurality of test pieces (round wire shape with a diameter of φ10 mm, no heat treatment) were prepared with different concentrations of 75 at %, 0.92 at %, 1.14 at %, 1.4 at % and 1.59 at %. Rotational forging was performed on these specimens. At this time, each test piece was evaluated as to how much processing rate the rotary forging could be performed.

As shown in FIG. 7, as a result of this evaluation test, test pieces with an O content of 0.26 to 1.14 at% can be rotary forged at a processing rate of 75% or more without any problem. was confirmed. A test piece with an O content of 1.4 at% was subjected to rotary forging at a processing rate of 50 to 75% without any problem, but cracks occurred when the processing rate exceeded 75%. A test piece having an O content of 1.59 at% was cracked when rotary forging was performed at a processing rate exceeding 50%. Therefore, in order to obtain good workability, the content of O is preferably 1.7 at% or less, more preferably 1.4 at% or less, when the entire titanium alloy is 100 at%. It is more preferable if it is 1.2 at % or less.

<Lower Limit of O Content (Evaluation of Titanium Alloy Structure)>
The lower limit of the O content is set particularly based on mechanical properties. In other words, conventional titanium alloys have a large amount of β phase, and since deformation occurs with a small force, there is a problem that the shape after forming cannot be maintained. For this reason, in the titanium alloy of the present embodiment, it is preferable that a certain amount of equiaxed α-phase is precipitated, which has the function of restraining the deformation of crystals, increasing the strength of the alloy, and preventing softening. As shown in FIGS. 4(B) and 4(C), the titanium alloy according to the present embodiment precipitates an equiaxed α-phase when aging treatment is performed after heat treatment. However, as already explained, if the content of O in the titanium alloy is not sufficient, Ta as a β-stable element functions more than O as an α-stable element, and even if aging treatment is performed, equiaxed α In some cases, the phase does not precipitate easily, and an aging treatment for several days is required for the precipitation of the equiaxed α-phase. If the O content is less than 0.4 at%, as shown in FIG. 4A, even if the aging treatment is performed for about 2 hours, the precipitation amount of the equiaxed α phase is not sufficient. Difficult to maintain shape. Therefore, the content of O when the entire titanium alloy is 100 at% is preferably 0.4 at% or more, more preferably 0.6 at% or more, and more preferably 0.75 at% or more (Fig. 4 (B )) is most preferred.

The titanium alloy according to the present embodiment has an extremely small amount of elution of metal ions of the constituent elements Ti, Ta, and Sn, exhibits excellent corrosion resistance, has low cytotoxicity, has high biocompatibility, and can be used in an external magnetic field. It is a non-magnetic material that is difficult to be magnetized by , and has a very low risk of adversely affecting medical equipment (such as MRI) that dislikes magnetism, and has high elasticity, moderate rigidity, and high workability. That is, the titanium alloy according to the present embodiment has lower cytotoxicity than conventional titanium alloys, and is excellent in magnetic properties, corrosion resistance, mechanical properties and workability. For this reason, medical guide wires, delivery wires, stents, aneurysm embolization coils, catheters such as vein filters, dental cleansers, reamers, files, orthodontic wires, etc., and artificial bones. It is suitable for medical instruments such as orthopedic field.

In addition, the method for producing a titanium alloy according to the present invention is not limited to the above-described embodiment. For example, vanadium (Va) group A powder composed of vanadium (Va) or niobium (Nb), which is another element of , may also be used. That is, the composition of the titanium alloy may contain vanadium (Va) or niobium (Nb), which is another element of the vanadium (Va) group, together with or instead of tantalum (Ta). . The titanium alloy obtained by this manufacturing method is extremely stable in quality. By the way, like tantalum, vanadium (Va) or niobium (Nb) also has a high melting point, so if only solid phase diffusion bonding is used, the internal composition of the titanium alloy tends to be uneven, and the quality of metal parts after cold working is reduced. Warranty becomes difficult.

However, the specific gravities of Va, Nb, and Ta are 5.96 (g/cm3), 8.40 (g/cm3), and 16.60 (g/cm3), respectively, and the specific gravity of titanium is 4.5 ( g/cm3). That is, the specific gravity of Va is slightly larger than that of titanium, but the specific gravity of Nb and Ta is slightly less than twice the specific gravity of titanium. For this reason, it is presumed that Nb and Ta cannot be uniformly diffused in the solidification process to a greater extent than Va. As a result, Nb, like Ta, can have a distribution similar to that shown in FIG. 3 during the solidification process. Therefore, it can be said that it is particularly important for Nb and Ta to be homogenized in the dissolution process as compared to Va.

The titanium alloy according to the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. For example, from the titanium alloy according to the present invention, medical guide wires, delivery wires, stents, clips, aneurysm embolization coils or vein filters, or dental cleansers, reamers, files or orthodontic wires are formed. A conventionally known method can be adopted as a method, and examples thereof include wire drawing, drawing, casting, forging, press working, and the like.

Next, examples of titanium alloys according to the present invention will be described.

<Tensile test 1>
The inventors of the present application performed a tensile test on the test piece T1 according to Example 1 and the test piece H1 according to Comparative Example 1, which were prepared using the titanium alloy according to the embodiment of the present invention with a different O content. rice field. FIG. 8A is a table showing compositions of test pieces T1 and H1 to be subjected to tensile tests. The test pieces T1 and H1 are round wires with a diameter of φ0.406 mm, which are subjected to cold working (wire drawing) such that the working ratio is 75%. Moreover, the test piece H1 according to Comparative Example 1 was produced using a titanium alloy having a composition of Ti-23Ta-3Sn-0.25O, and the O content was small. A test piece T1 according to Example 1 was produced using a titanium alloy having a composition of Ti-23Ta-3Sn-0.8O. The titanium alloys constituting the test pieces T1 and H1 were heat-treated at 890° C. for 1 minute, but not aged. A tensile test was performed on the above test pieces T1 and H1 using a tensile tester. As the measurement conditions, the distance between marks was 50 mm, and the tensile speed was 2 mm/min.

FIG. 8(B) shows a stress-strain diagram obtained as a result of performing a tensile test on the test pieces T1 and H1. Until the stress reaches around 200 MPa, the test pieces T1 and H1 are deformed so that similar strain occurs. The graph has an inflection point K1 when the stress is around 200 MPa. As shown in FIG. 8(B), in the test piece H1, after the inflection point K1, the slope of the graph becomes much gentler than the slope up to that point, and it is presumed that there is a yield region in the middle. (Refer to the dotted circle area in FIG. 8B). On the other hand, in the test piece T1, as shown in FIG. 8(B), after the inflection point K1, the slope of the graph becomes gentler than the slope up to that point, as in the case of the test piece H1. is steeper than that of the test piece H1 (see the dotted circle area in FIG. 8(B)). That is, regardless of the presence or absence of aging treatment, the test piece T1 of Example 1, which has a high O content, can be said to have harder (harder to yield) material properties than the test piece H1 of Comparative Example 1. It can be said that the shape of the product can be stabilized.

<Tensile test 2>
FIG. 9(A) is a stress-strain diagram obtained as a result of performing a tensile test in which stress-strain was repeatedly applied to the test piece H1 of Comparative Example 1 under the same measurement conditions as in Tensile Test 1. be. FIG. 9(B) is a stress-strain diagram obtained as a result of performing a tensile test in which repeated stress-strain was applied to the test piece T1 of Example 1 under the same measurement conditions as in tensile test 1. be. FIG. 9(C) is a diagram in which the stress-strain diagrams of FIGS. 9(A) and (B) are superimposed. As is clear from FIG. 9(C), when a tensile stress of slightly less than about 500 (MPa) is applied to the test piece H1 to strain it by about 2% and then the load is removed, a permanent strain of about 0.35% remains. On the other hand, when a tensile stress of slightly less than about 500 (MPa) is applied to the test piece T1 to strain it by about 2% and then unload it, only about 0.2% permanent strain remains. As a result, it was confirmed that the test piece T1 of Example 1, in which the O content was increased, had a higher elastic limit than the test piece H1 of Comparative Example 1.

<Tensile test 3>
In addition, the inventor of the present application conducted a tensile test on the test piece T2 according to Example 2, which was created using the titanium alloy according to the embodiment of the present invention with a different O content, and the test piece H2 according to Comparative Example 2. did FIG. 10(A) is a table showing the composition of the test pieces T2 and H2 to be subjected to the tensile test. The composition of the titanium alloys constituting the test pieces T2 and H2 is obtained by adding aging treatment at 300° C. for 1 hour to the titanium alloys constituting the test piece T1 of Example 1 and the test piece H2 of Comparative Example 1. becomes. A tensile test was performed on the above test pieces T2 and H2 using a tensile tester. As the measurement conditions, the distance between marks was 50 mm, and the tensile speed was 2 mm/min.

FIG. 10(B) shows a stress-strain diagram obtained as a result of performing a tensile test on the test pieces T2 and H2. Until the stress reaches around 200 MPa, the test pieces T2 and H2 are deformed so that similar strain occurs. The graph has an inflection point K2 when the stress is around 200 MPa. As shown in FIG. 10(B), for the test piece H2, the slope of the graph after the point of inflection K2 becomes much gentler than the slope up to that point (see the dotted circle area in FIG. 10(B)). On the other hand, in the test piece T2, as shown in FIG. 10(B), the slope of the graph after the inflection point K2 becomes gentler than the slope up to that point as in the case of the test piece H2, but the slope of the graph is steeper than that of test piece H2 (see the dotted circle area in FIG. 10(B)). In other words, it can be said that even after the aging treatment, the test piece T2 has material properties that are harder (harder to yield) than the test piece H2, and it can be said that the shape of the molded product can be stabilized.

When the test pieces T2 and H2 are compared with the test pieces T1 and H1, the degree of inclination of the graph after the point of inflection is steeper for the test pieces T2 and H2 than for the test pieces T1 and H1. This is because the aged titanium alloy contains more equiaxed α-phase than the unaged titanium alloy, so it has the properties of a hard metal. do. As a result, it can be said that the titanium alloy of the present embodiment that has undergone aging treatment is easier to form after cold working.

Furthermore, when comparing the results of tensile test 1 of test piece T1 of Example 1 (see FIG. 8(B)) and the results of tensile test 3 of test piece T2 of Example 2 (see FIG. 10(B)), As shown in FIG. 12A, even if the same stress is applied to the test piece T2, the strain caused by the test piece T2 is smaller than that of the test piece T1 until the stress section where the graphs intersect each other is less than 800 (MPa). Moreover, after the stress of each of the test pieces T1 and T2 reaches the maximum value (tensile strength), the strain of both the test pieces T1 and T2 increases with substantially constant stress (tensile strength). Incidentally, the maximum stress value (tensile strength) of the test piece T1 is about 870 (MPa), and the maximum stress value (tensile strength) of the test piece T2 is about 840 (MPa). The test piece T2 has about 1.2 times the strain at which it breaks as compared with the test piece T1. From this result, the titanium alloy that was subjected to aging treatment, compared to the titanium alloy that was not subjected to aging treatment, precipitated more equiaxed α-phase and exhibited harder properties, and also improved ductility. I can say

<Tensile test 4>
FIG. 11A is a stress-strain diagram obtained as a result of a tensile test in which the test piece H2 was subjected to repeated stress-strain under the same measurement conditions as in tensile test 3. FIG. FIG. 11B is a stress-strain diagram obtained as a result of a tensile test in which the test piece T2 was subjected to repeated stress-strain under the same measurement conditions as in tensile test 3. FIG. FIG. 11(C) is a diagram in which the stress-strain diagrams of FIGS. 11(A) and (B) are superimposed. As is clear from FIG. 11(C), when the test piece H2 is unloaded after being distorted by about 0 to 2%, a permanent strain of about 0.2% remains. On the other hand, if the test piece T2 is similarly strained by about 0 to 2% and then unloaded, only a little less than about 0.1% permanent strain remains. As a result, it was confirmed that the test piece T2, in which the O content was increased, had a higher elastic limit than the test piece H2.

Furthermore, when comparing the results of tensile test 2 of test piece T1 of Example 1 (see FIG. 9B) with the results of tensile test 4 of test piece T2 of Example 2 (see FIG. 11B), As shown in FIG. 12(B), for example, a test piece T1 that has not been subjected to aging treatment has a tensile stress of about 500 (MPa), is strained by about 2%, and then unloaded, the strain is reduced to 0.2%. Strain occurs, but when the test piece T2 subjected to aging treatment is strained by about 2% by applying a tensile stress of about 600 (MPa) and then unloaded, only a little less than 0.1% strain is generated. In other words, it can be said that the aged titanium alloy has a higher elastic limit than the unaged titanium alloy.

<Vickers hardness test>
In addition, the inventors of the present application have tested the test piece T3 of Example 3-1 and the test piece T4 of Example 3-2, which were prepared using the titanium alloy according to the embodiment of the present invention with a different O content. A Vickers hardness test was performed. In this Vickers hardness test, 10 measurement points were used, and a load of 0.1 (N) was applied to the measurement points. A test piece H3 of Comparative Example 3 was also prepared and subjected to the Vickers hardness test in the same manner.

FIG. 13A is a table showing compositions of test pieces T3, T4, and H3 to be subjected to the Vickers hardness test. The test pieces T3, T4, and H3 are round wires with a diameter of φ0.517 mm. Also, the test piece H3 was produced using a titanium alloy having a composition of Ti-23Ta-3Sn-0.25O, and the O content was small. The test piece T3 was made using a titanium alloy with a composition of Ti-23Ta-3Sn-0.6O, and the test piece T4 was made using a titanium alloy with a composition of Ti-23Ta-3Sn-0.8O. It was created by Then, the test pieces T3, T4, and H3 were not heat-treated, and the test pieces T3, T4, and H3 were heat-treated at 450°C, 500°C, 550°C, 650°C, 700°C, and 750°C. A product after 30 minutes was prepared.

The results of this Vickers hardness test are shown in FIG. 13(B). As shown in FIG. 13(B), the test pieces T3, T4, and H3 did not change significantly due to the heat treatment up to the heat treatment temperature of 550°C. On the other hand, it was confirmed that in the heat treatment at 650° C. or higher, the hardness of the titanium alloy tends to increase as the O content increases. That is, when the content of O is increased, the heat treatment temperature is preferably 600°C to 1000°C, more preferably 700°C to 900°C.

From the above <Tensile test 1> to <Tensile test 4> and <Vickers hardness test>, it was confirmed that the elastic limit and the strength of the material were improved by increasing the O content. As a result, it was found that if the content of O is moderately increased, the titanium alloy can be easily post-processed and has moderate hardness and elastic limit.

The titanium alloy and the method for producing the titanium alloy of the present invention are not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

The titanium alloy of the present invention is used in the field of catheters such as guide wires, delivery wires, stents, clips, aneurysm embolization coils or vein filters for medical use, or in the dental field such as cleansers, reamers, files or orthodontic wires for dental treatment. It can be used in fields such as orthopedic fields such as artificial bones.

REFERENCE SIGNS LIST 1 HIP device 2 HIP container 3 HIP furnace 3A heat insulating part 3B gas introduction passage 4 heater 5 mixed powder 6 consumable electrode 8 arc melting furnace 9 rod 10 molten metal pool 11 ingot

Claims (8)

A mixing step of mixing at least a titanium powder containing titanium (Ti) as a main component and a group Va powder containing a vanadium (Va) group element as a main component to obtain a mixed powder;
a solidification step of obtaining a solidified body by heating the mixed powder mixed in the mixing step for solid-phase diffusion bonding;
a melting step of heating and melting the solidified body to form a titanium alloy;
characterized by comprising
A method for producing a titanium alloy. In the solidification step, the mixed powder is solid phase diffusion bonded by heating at any temperature between 900 and 1400 ° C.
A method for producing a titanium alloy according to claim 1. In the solidification step, the mixed powder is placed under a vacuum, and the mixed powder is solid phase diffusion bonded by heating and pressing,
A method for producing a titanium alloy according to claim 1 or 2. In the melting step, the solidified body is melted by a vacuum arc remelting method or a cold crucible induction melting method,
A method for producing a titanium alloy according to any one of claims 1 to 3. The titanium alloy contains 0.4 to 1.7 at% oxygen (O) when the whole is 100 atomic% (at%),
A method for producing a titanium alloy according to any one of claims 1 to 4. The Va group powder is mainly composed of tantalum (Ta) or niobium (Nb),
A method for producing a titanium alloy according to any one of claims 1 to 5. The titanium alloy contains 1 to 8 at% tin (Sn) when the whole is 100 atomic% (at%),
A method for producing a titanium alloy according to any one of claims 1 to 6. a heat treatment step of heat-treating the titanium alloy produced in the melting step;
an aging treatment step of performing an aging treatment on the heat-treated titanium alloy;
with
The titanium alloy that has undergone the melting step contains 15 to 27 at% tantalum (Ta), 1 to 8 at% tin (Sn), and 0.4 to 1.7 atomic % of oxygen (O) and the balance consisting of titanium (Ti) and unavoidable impurities,
In the aging treatment step, the titanium alloy is subjected to aging treatment for 24 hours or less to precipitate an α phase in the titanium alloy.
A method for producing a titanium alloy according to any one of claims 1 to 7.

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