Manufacturing method for titanium alloys

Abstract

A method for producing a titanium alloy that allows for easy control of the amount of oxygen contained in the titanium alloy. [Solution] The method for producing a titanium alloy of the present invention includes at least a mixing step of mixing titanium powder containing titanium (Ti) as a main component with Va-group powder containing vanadium group elements as a main component to obtain a mixed powder, a solidification step of heating the mixed powder mixed in the mixing step to form a solidified body by solid-state diffusion bonding, and a melting step of heating and melting the solidified body to produce a titanium alloy. In the solidification step, the mixed powder is solid-state diffusion bonded by heating and pressurization. In the melting step, the solidified body is melted by vacuum arc remelting or cold crucible induction melting.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a titanium alloy.

Background Art

[0002] Conventionally, as a method for manufacturing a titanium alloy, for example, columnar titanium and wire-shaped or thin-plate-shaped additive metals are set in a crucible of a floating melting apparatus, and these are melted under predetermined melting conditions and then naturally cooled in the crucible to obtain a titanium alloy (see, for example, Patent Document 1). Further, as a method for manufacturing a titanium alloy, for example, titanium powder and powder of a vanadium group element are mixed and set in a heating container, and these are pressurized and heated to be sintered to obtain a titanium alloy (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in a titanium alloy, generally, it is preferable to minimize the content of oxygen which becomes an inevitable impurity. However, when attempting to actively incorporate oxygen into the titanium alloy, in the method for manufacturing a titanium alloy of Patent Document 1, during melting, elements in the atmosphere are mixed into the titanium alloy, making it difficult to precisely control the composition of the titanium alloy. As a result, in the manufacturing method of Patent Document 1, there was a problem that the amount of oxygen could not be controlled in the first place.

[0005] Furthermore, according to the inventors' research, the titanium alloy manufacturing method described in Patent Document 2 had the problem that titanium and vanadium group elements diffused unevenly in the titanium alloy after sintering. As a result, the manufacturing method in Patent Document 2 also had the problem that oxygen contained in the oxide film of the titanium powder diffused unevenly.

[0006] In view of these circumstances, the present invention aims to provide a method for manufacturing a titanium alloy that can homogenize the entire alloy while precisely controlling the composition ratio contained in the titanium alloy. [Means for solving the problem]

[0007] The present invention provides a method for producing a titanium alloy, comprising at least a mixing step of mixing titanium powder mainly composed of titanium (Ti) and vanadium group element powder mainly composed of vanadium group elements to obtain a mixed powder; a solidification step of heating the mixed powder mixed in the mixing step to induce 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.

[0008] The solidification process is characterized by heating the mixed powder at a temperature between 900 and 1400°C to induce solid-phase diffusion bonding.

[0009] In the present invention, a method for producing a titanium alloy is characterized in that, in the solidification step, the mixed powder is subjected to a vacuum and solid-phase diffusion bonding by heating and pressurizing.

[0010] In the present invention, a method for producing a titanium alloy is characterized in that the solidified material is dissolved in the melting step by a vacuum arc remelting method or a cold crucible induction melting method.

[0011] The present invention relates to a method for producing a titanium alloy, characterized in that the titanium alloy contains 0.4 to 1.7 at% oxygen (O) when the total composition is 100 atomic percent (at%).

[0012] The present invention relates to a method for producing a titanium alloy, characterized in that the Va group powder mainly consists of tantalum (Ta) or niobium (Nb).

[0013] The present invention relates to a method for producing a titanium alloy, characterized in that the titanium alloy contains 1 to 8 at% tin (Sn) when the total composition is 100 atomic percent (at%).

[0014] The present invention provides a method for producing a titanium alloy, further comprising a heat treatment step of heat treatment on the titanium alloy produced in the melting step, and an aging treatment step of aging treatment on the heat-treated titanium alloy, wherein the titanium alloy obtained through the melting step consists of 15 to 27 at% tantalum (Ta), 1 to 8 at% tin (Sn), 0.4 to 1.7 at% oxygen (O), and the remainder being titanium (Ti) and unavoidable impurities, when the total composition is 100 atomic percent (at%), and the aging treatment step is characterized by performing an aging treatment on the titanium alloy for 24 hours or less to precipitate an α phase in the titanium alloy. [Effects of the Invention]

[0015] The present invention provides an excellent method for manufacturing titanium alloys, which allows for high-precision control of the compositional ratio contained in the titanium alloy while homogenizing each component of the titanium alloy. [Brief explanation of the drawing]

[0016] [Figure 1] This flowchart shows the process for manufacturing a titanium alloy in an embodiment of the present invention. [Figure 2] (A) is a schematic diagram of a HIP apparatus used in the titanium alloy manufacturing method according to an embodiment of the present invention. (B) is a schematic diagram of an apparatus for performing vacuum arc remelting (VAR) used in the titanium alloy manufacturing method according to an embodiment of the present invention. [Figure 3](A) is a photograph of a SEM image when the solidified body generated by HIP treatment is observed at a magnification of 400 times using a scanning electron microscope (SEM). (B) is a photograph of a SEM image when elemental analysis of Ti is performed using X-rays within the range of (A). (C) is a photograph of a SEM image when elemental analysis of Ta is performed using X-rays within the range of (A). (D) is a photograph of a SEM image when elemental analysis of Sn is performed using X-rays within the range of (A). [Figure 4] (A) is a photograph of a TEM image when the surface of a comparative titanium alloy (Ti-23.4Ta-3.4Sn―0.26O) serving as a comparative example is observed at a magnification of 2000 times using a transmission electron microscope (TEM). (B) is a photograph of a TEM image when the surface of a first titanium alloy (Ti-23.4Ta-3.4Sn―0.75O) is observed at a magnification of 2000 times using a transmission electron microscope (TEM). (C) is a photograph of a TEM image when the surface of a second titanium alloy (Ti-23.4Ta-3.4Sn―0.92O) is observed at a magnification of 2000 times using a transmission electron microscope (TEM). Note that the numerical values attached to the elemental notations of Ta, Sn, and O within each parentheses corresponding to the comparative titanium alloy and the first and second titanium alloys represent the atomic % (at%) values of each element (Ta, Sn, O) when the entirety of the comparative titanium alloy and the first and second titanium alloys is taken as 100 atomic % (at%). [Figure 5] It is a binary phase diagram of Ta-Ti. [Figure 6] It is a graph showing the results of a cold working property evaluation test for a titanium alloy (Ti-23Ta-xSn―0.26O) in which the Ta content is 23 at% and the Sn content is x (at%) and the O content is 0.26 at% when the whole is taken as 100 atomic % (at%). [Figure 7] It is a table showing the results of a cold working property evaluation test for a titanium alloy (Ti-23.4Ta-3.4Sn―xO) in which the Ta content is 23.4 at% and the Sn content is 3.4 at% and the O content is x (at%) when the whole is taken as 100 atomic % (at%). [Figure 8](A) is a table showing the compositions of test pieces H1 and T1 made using the titanium alloy in an embodiment of the present invention. (B) is a stress-strain diagram which is the result of a tensile test for each of test pieces H1 and T1. [Figure 9] (A) is a stress-strain diagram obtained as a result of performing a tensile test in which repeated stress-strain was applied to test piece H1. (B) is a stress-strain diagram obtained as a result of performing a tensile test in which repeated stress-strain was applied to test piece T1. (C) is a diagram in which the stress-strain diagrams of (A) and (B) are superimposed. [Figure 10] (A) is a table showing the compositions of test pieces H2 and T2 made using the titanium alloy in an embodiment of the present invention. (B) is a stress-strain diagram which is the result of a tensile test for each of test pieces H2 and T2. [Figure 11] (A) is a stress-strain diagram obtained as a result of performing a tensile test in which repeated stress-strain was applied to test piece H2. (B) is a stress-strain diagram obtained as a result of performing a tensile test in which repeated stress-strain was applied to test piece T2. (C) is a diagram in which the stress-strain diagrams of (A) and (B) are superimposed. [Figure 12] (A) is a diagram in which the stress-strain diagrams which are the results of tensile tests for each of test pieces T1 and T2 are superimposed. (B) is a diagram in which the respective stress-strain diagrams obtained as a result of performing a tensile test in which repeated stress-strain was applied to each of test pieces T1 and T2 are superimposed. [Figure 13] (A) is a table showing the compositions of test pieces H3, T3, and T4 made using the titanium alloy in an embodiment of the present invention. (B) is a graph showing the results of Vickers hardness tests for each of a plurality of test pieces H3, T3, and T4 with different heat treatment temperatures.

Embodiments for Carrying Out the Invention

[0017] The method for manufacturing a titanium alloy according to embodiments of the present invention will be described below with reference to the attached drawings. The method for manufacturing a titanium alloy according to embodiments of the present invention will be described below with reference to Figures 1 and 2.

[0018] <Mixing process> First, as shown in Figure 1, a mixing step is performed in which Ti powder, mainly composed of titanium (Ti), Ta powder, mainly composed of tantalum (Ta), and Sn powder, mainly composed of tin (Sn), are prepared and mixed in a predetermined mixing ratio (step S100). In this embodiment, the Ti powder, Ta powder, and Sn powder are assumed to have a particle size that can pass through a sieve with a mesh size of 325 (mesh / inch) or less. Preferably, the Ti powder contains 90% or more titanium (Ti), more preferably 95% or more titanium (Ti), and even more preferably 99% or more titanium (Ti). In this case, the remaining components of the Ti powder include components other than titanium (Ti). Furthermore, the titanium (Ti) in the Ti powder may include pure titanium (Ti) or titanium (Ti) having an oxide film. The above Ta powder preferably contains 90% or more tantalum (Ta), more preferably 95% or more tantalum (Ta), and even more preferably 99% or more tantalum (Ta). In this case, the remaining components of the Ta powder include components other than tantalum (Ta). Furthermore, the tantalum (Ta) in the above Ta powder may be pure tantalum (Ta) or tantalum (Ta) having an oxide film. The above Sn powder preferably contains 90% or more tin (Sn), more preferably 95% or more tin (Sn), and even more preferably 99% or more tin (Sn). In this case, the remaining components of the Sn powder include components other than tin (Sn). Furthermore, the tin (Sn) in the above Sn powder may be pure tin (Sn) or tin (Sn) having an oxide film.

[0019] For the same weight, powders with smaller particle sizes have a greater number of particles than powders with larger particle sizes. As a result, when compared by the same weight, powders with smaller particle sizes have a larger surface area that reacts with oxygen than powders with larger particle sizes. Titanium powder (Ti) and tantalum powder (Ta) are stable in the atmosphere due to their oxide film. As a result, when compared by the same weight, mixing in titanium powder (Ti) or tantalum powder (Ta) with smaller particle sizes results in a higher oxygen content in the final titanium alloy product than mixing in powders with larger particle sizes. Therefore, the particle size of titanium powder (Ti) and tantalum powder (Ta) affects the oxygen content in the titanium alloy, and the oxygen content in the titanium alloy can be adjusted by appropriately selecting the particle size of each powder. For this reason, to create multiple titanium alloys with different oxygen content, it is sufficient to change the particle size of at least one of the Ti or Ta powders. Furthermore, if the desired oxygen content cannot be achieved simply by reducing the particle size of the Ti powder and / or Ta powder, titania powder may be added as it contains oxygen itself.

[0020] For example, when the total is considered to be 100 atomic percent (at%), the mixture consists of 15-27 at% tantalum (Ta), 1-8 at% tin (Sn), 0.4-1.7 at% oxygen (O), with the remainder being titanium (Ti) and unavoidable impurities. The Ti powder or titania powder, Ta powder, and Sn powder are uniformly mixed in this ratio. Converting this to weight percentage, when the total is considered to be 100 wt%, Ta will be 40-56 wt%, Sn will be 2-10 wt%, O will be 0.1-0.3 wt%, and the remainder will be titanium (Ti) and unavoidable impurities. For example, in the case of a titanium alloy Ti-23.4Ta-3.4Sn-xO, when the total is considered to be 100 wt%, the mixture will consist of 52 wt% Ta powder, 5 wt% Sn powder, and the remainder being Ti powder or titania powder. The O content is adjusted by controlling the particle size of Ti powder or Ta powder having an oxide film on its surface, or by using titania powder. In this embodiment, since the Sn powder content is low, it is presumed that the influence of Sn powder on the O content is small. The notation at% represents atomic percentage, and below, the notation at% is used to represent the atomic percentage of the corresponding element when the entire titanium alloy is considered to be 100 atomic percent (at%). In addition, below, the numerical values ​​attached to the elemental notations of Ta, Sn, and O representing the composition of the titanium alloy (see the values ​​in parentheses immediately following "titanium alloy" below) represent the atomic percentage (at%) of each element (Ta, Sn, O) when the entire titanium alloy is considered to be 100 atomic percent (at%).

[0021] <Solidification process> Next, as shown in Figure 1, the mixed powder of Ti powder or titania powder, Ta powder, and Sn powder (hereinafter simply referred to as "mixed powder"), which has been uniformly mixed in the above mixing step, is subjected to a solidification step (step S101) under vacuum, in which the mixed powder is solidified by solid-phase diffusion bonding. The mixed powder becomes a solidified body through the solidification step. Since the mixed powder is solidified by solid-phase diffusion bonding under vacuum, it is possible to limit the entry of unintended oxygen (O) from the outside air into the solidified body. In this embodiment, the solidified body refers to a mass formed by solid-phase diffusion bonding of the mixed powder. In the solidification step, for example, a normal heat treatment (e.g., sintering treatment by heating), or a pressurized and heated treatment performed simultaneously with pressurization is employed. For pressurization and heating, one of the following methods is used: Hot Isostatic Pressing (HIP), Spark Isostatic Pressing (SIP), or Spark Plasma Sintering (SPS). The mixed powder is solidified by one of these methods. Incidentally, HIP and SIP are isotropic (hydrostatic) pressurization methods, while SPS uses a press machine and mold, so it is directional pressurization (axial pressurization). In this embodiment, the pressure under vacuum in which the mixed powder is placed is, for example, 1.0 × 10⁻⁶. -1 (Pa) or less is preferred, and 1.0 × 10 -2 ~1.0×10 -5 A range within (Pa) is more preferable, and 1.0 × 10 -2 ~1.0×10 -3 A range within (Pa) is even more preferable.

[0022] Here, referring to Figure 2(A), we will explain using the case where the solidification process uses the hot isostatic pressing method (hereinafter referred to as HIP treatment) as an example. First, the mixed powder 5 is pressurized and filled into the HIP container 2. The HIP container 2 is composed of, for example, a cylindrical container with one end open and the other end closed, and a lid. The mixed powder 5 is compressed and filled into the cylindrical container, and the cylindrical container is placed in the vacuum chamber of an electron beam apparatus (not shown). Then, the pressure inside the vacuum chamber is set to, for example, 1.0 × 10⁻⁶ -2 ~1.0×10 -3 Electron beam welding is performed under a vacuum within the range of (Pa), and a lid is welded to the opening of the HIP container 2 to seal it. As a result, the mixed powder is placed under vacuum inside the HIP container 2.

[0023] While it is preferable to use a material other than Ta for the HIP container 2, Ta is extremely expensive and not practical for mass production. Therefore, for example, it is preferable to use a material mainly composed of Ti or iron as the material for the HIP container 2, and more preferably a material mainly composed of iron. Incidentally, in a typical HIP treatment, the HIP container 2 is made from the same material as the material with the highest melting point among the mixed powders 5 (in this case, Ta).

[0024] Then, the HIP container 2 is placed inside the heat-insulating section 3A of the HIP furnace 3 of the HIP device 1. The HIP device 1 is configured to create a high-temperature, high-pressure atmosphere inside the heat-insulating section 3A of the HIP furnace 3 by heating with a substantially inert gas such as argon and a heater 4. The gas is supplied from the outside to the inside of the HIP furnace 3 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 undergoes solid-phase diffusion bonding and becomes a solidified body. Since the mixed powder 5 is sealed inside the HIP container 2 under vacuum, even if the mixed powder 5 is pressurized and heated through the HIP container 2, it is possible to limit the entry of unintended oxygen (O) from the outside air into the solidified body. Incidentally, immediately after the HIP treatment, the HIP container 2 and the solidified body are firmly bonded together. Therefore, in order to separate the HIP container 2 from the solidified body, the HIP container 2 and the layer in which the HIP container 2 and the solidified body are mixed are cut using a machine tool. As a result, only the solidified body remains. This forms a cylindrical solidified body.

[0025] In the HIP treatment, the internal temperature of the HIP furnace 3 of the HIP apparatus is set to, for example, 1000°C, the pressure to 98 MPa, and the HIP container is left under these conditions for a predetermined time to form a solidified body. The internal temperature of the HIP furnace 3 can be any range as long as the HIP container 2 is not damaged or melted. For example, the internal temperature of the HIP furnace 3 is preferably 700°C to 1600°C, more preferably 900°C to 1400°C, and even more preferably 1000°C to 1200°C. The internal pressure of the HIP furnace 3 is preferably 50 to 200 MPa, more preferably 70 to 180 MPa, and even more preferably 90 to 120 MPa.

[0026] Note that the melting point of Ta is quite high at 3017°C. Even if the internal temperature of the HIP furnace 3 is set to, for example, 900°C to 1400°C, if the proportion of Ta is high, such as in the titanium alloy of this embodiment (15 at% or more), the possibility of each powder diffusing completely uniformly is low. In other words, the solidified body produced by the HIP treatment may contain regions where Ta, Sn, Ti, and O are not uniformly diffused, and where Ta, Sn, Ti, or O are unevenly distributed. To confirm this, the inventors of this 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, and solidified the mixed powder (with a Ta powder content of 23.4 at%, a Sn powder content of 3.4 at%, and the remainder being Ti powder, with a particle size of 10 to 45 μm for each powder) as described above. Using a scanning electron microscope (SEM) and X-rays, they investigated how Ta, Sn, and Ti were distributed in the solidified body. The results are shown in Figures 3(A) to (D). Figure 3(A) is a SEM image of the solidified material observed at 400x magnification using a scanning electron microscope (SEM). As shown in Figures 3(B) to (D), the distribution of Ti, Ta, and Sn within the range of the SEM image in Figure 3(A) is not uniform, indicating that the Ti powder, Ta powder, and Sn powder are not uniformly diffused. From this, it was confirmed that, at an internal temperature of HIP furnace 3 of approximately 900°C to 1400°C, the possibility of complete alloying of the Ti powder, Ta powder, and Sn powder with this composition, where the proportion of Ta is very high, is low.

[0027] On the other hand, raising the internal temperature of the HIP furnace 3 to a temperature higher than the above temperature can lead to damage to the HIP container 2 itself, and consequently, a malfunction of the HIP furnace 3 itself. Furthermore, in order to achieve heating at temperatures higher than 1400°C, it is conceivable to form the HIP container 2 from a material that can withstand high temperatures (for example, Ta), but as already mentioned, using Ta material for the HIP container 2 would make it extremely expensive and therefore impractical.

[0028] <Dissolution process> Next, as shown in Figure 1, a dissolution step is performed to dissolve the solidified mixed powder solidified in the above solidification step (step S102). The solidified body is dissolved in the dissolution step, becoming a titanium alloy ingot. As described above, the solidified body does not have uniform diffusion of each component, but by performing the dissolution step, each component is uniformly melted (dissolved), and a titanium alloy ingot in which each component is uniformly dispersed can be obtained. In the dissolution step, it is preferable to dissolve the solidified body at a temperature that can simultaneously dissolve Ta, Sn, and Ti, which have different melting points, in order to simultaneously dissolve and uniformly diffuse them. In the melting process, one of the following methods is used, for example: Vacuum Arc Remelting (VAR), ElectroSlag Remelting (ESR), Vacuum Induction Melting (VIM), Cold Crucible Induction Melting (CCIM), Plasma Arc Melting (PAM), or Electron Beam Melting (EBM), and the solidified material is melted by one of these methods.

[0029] Here, referring to Figure 2(B), we will explain using the case where the vacuum arc remelting method (VAR) is used in the melting process as an example. First, the cylindrical solidified body prepared in the solidification process is used as a consumable electrode 6 and is connected to a rod 9 suspended inside the arc melting furnace 8. As a result, the consumable electrode 6 is suspended and supported by the rod 9 inside the arc melting furnace 8 with the molten metal pool 10 located directly below it. In this state, when an electric current is passed through the rod 9 to the consumable electrode 6, 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 then accumulates below to form a titanium alloy ingot 11.

[0030] Alternatively, the titanium alloy ingot 11 may be used as a consumable electrode 6, connected to the rod 9, and then placed in the arc melting furnace 8 as described above, and melted again by applying current. This process can be repeated multiple times to increase the reliability of homogenization of each component, and therefore may be repeated even further. In this manner, the titanium alloy is prepared.

[0031] <Cold working process> Next, as shown in Figure 1, cold working is performed on the titanium alloy ingot prepared in the melting process (step S103). Cold working of the titanium alloy ingot forms titanium alloy workpieces such as wires and rods.

[0032] <Heat treatment process> Next, as shown in Figure 1, a heat treatment step is performed on the titanium alloy workpiece formed in the cold working step (step S104). The heat treatment temperature is preferably 600°C to 1000°C, and more preferably 700°C to 900°C.

[0033] <Statute of Limitations Treatment Process> Next, as shown in Figure 1, an aging treatment is performed on the titanium alloy that has been heat-treated in the above heat treatment step (step S105). The aging treatment temperature is preferably 200°C to 550°C, and more preferably 300°C to 500°C. When the titanium alloy in this embodiment is subjected to the above aging treatment for a predetermined time, equiaxed α phases and the like precipitate in the titanium alloy. Note that the α phase is not limited to equiaxed structures, but may include other forms as well.

[0034] Figures 4(B) and 4(C) show TEM images of the surfaces of the first titanium alloy (Ti-23.4Ta-3.4Sn-0.75O) and the second titanium alloy (Ti-23.4Ta-3.4Sn-0.92O) in this embodiment, observed at a magnification of 2000x using a transmission electron microscope (TEM). Figure 4(A) shows a TEM image of a comparative example titanium alloy (Ti-23.4Ta-3.4Sn-0.26O) under the same conditions as above. The first and second titanium alloys and the comparative titanium alloy were heat-treated at 890°C for 2 hours, followed by aging treatment at 300°C for 2 hours.

[0035] TEM images of the first and second titanium alloys shown in Figures 4(B) and (C) show the deposition of a white equiaxed α phase. The image in Figure 4(C), which has a higher O content, shows more equiaxed α phase deposition than the image in Figure 4(B). On the other hand, the TEM image of the comparative titanium alloy shown in Figure 4(A) shows almost no deposition of the white equiaxed α phase. It was confirmed that the equiaxed α phase precipitates even after aging treatment of about 2 hours in alloys with a high O content, as shown in Figures 4(B) and (C), but does not precipitate in alloys with a low O content, as shown in Figure 4(A), after aging treatment of about 2 hours. From these results, it was confirmed that the amount of equiaxed α phase deposition in titanium alloys can be controlled by the O content and the aging treatment time. It was found that the O content, when the total titanium alloy is considered to be 100 at%, is preferably 0.4 at% or higher, more preferably 0.6 at% or higher, and most preferably 0.75 at% or higher.

[0036] Incidentally, analysis of the TEM images shown in Figures 4(B) and (C) revealed that the average grain size of the equiaxed α phase in the first titanium alloy (Ti-23.4Ta-3.4Sn-0.75O) was 0.13 μm. Furthermore, 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 these results, it can be inferred that as the O content increases, the average grain size of the equiaxed α phase precipitated by 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 between 0.05 and 1.00 μm, more preferably between 0.05 and 0.50 μm, and even more preferably between 0.05 and 0.30 μm.

[0037] Furthermore, analysis of the TEM image of the first titanium alloy shown in Figure 4(B) revealed that the area ratio of the equiaxed α phase in the first titanium alloy (Ti-23.4Ta-3.4Sn-0.75O) 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 Figure 4(C) was 5.24%. The area ratio of the equiaxed α phase refers to the proportion of the area occupied by the equiaxed α phase per unit area in the TEM images of the cross-sections shown in Figures 4(B) and (C). From these results, it can be inferred that as the O content increases, the area ratio of the equiaxed α phase precipitated by aging treatment increases accordingly. In the titanium alloy of the present invention, the area ratio of the equiaxed α phase is preferably between 0.1% and 20%, more preferably between 0.1% and 15%, and even more preferably between 0.1% and 10%.

[0038] As described above, even with the same aging treatment time, a higher oxygen content in the titanium alloy results in a greater amount of equiaxed α phase precipitation, while a lower oxygen content results in a smaller amount of equiaxed α phase precipitation. Therefore, when precipitation of a specific amount of equiaxed α phase in a titanium alloy through aging treatment, a titanium alloy with a higher oxygen content requires a shorter aging treatment time than a titanium alloy with a lower oxygen content.

[0039] However, the equiaxed α phase increases the strength of titanium alloys. However, if the oxygen content becomes too high, it exceeds the solid solution limit of oxygen, and TiO and TiO2 are formed, reducing workability. This is reflected in the cold workability evaluation test shown in Figure 7, which will be discussed later.

[0040] While general titanium alloys also contain small amounts of oxygen as an unavoidable impurity, the oxygen content in such cases is 0.2 at% or less when the total titanium alloy is considered to be 100 at%. In such titanium alloys, ta, as a β-stable element, functions more than oxygen, as an α-stable element, and equiaxed α phases do not precipitate easily even with aging treatment, requiring aging treatment for several days. On the other hand, in titanium alloys like the one in this embodiment, if the oxygen content is actively increased and reaches 0.4 at%, oxygen functions as an α-stable element, and a minimum amount of equiaxed α phase precipitates after 12 hours of aging treatment, and a sufficient amount of equiaxed α phase precipitates after 24 hours of aging treatment. Furthermore, when the oxygen content in the titanium alloy reaches 1.7 at%, oxygen functions sufficiently as an α-stable element, and a sufficient amount of equiaxed α phase precipitates even after 1 hour of aging treatment. For this reason, the aging treatment time is preferably 1 to 24 hours, and more preferably 1 to 4 hours.

[0041] <Composition of Titanium Alloy> Next, an example of a titanium alloy produced by the above-described titanium alloy manufacturing method will be explained. In the embodiment of the present invention, when the total composition is 100 atomic percent (at%), the titanium alloy consists of 15 to 27 at% tantalum (Ta), 1 to 8 at% tin (Sn), 0.4 to 1.7 at% oxygen (O), and the remainder being titanium (Ti) and unavoidable impurities. The content of the remaining titanium (Ti) is not particularly limited; it is sufficient that titanium (Ti) is the most abundant element among the constituent elements when considered in terms of atomic ratio.

[0042] Furthermore, titanium alloys are broadly classified into three types: α-type titanium alloys, which have a close-packed hexagonal (HCP) α-phase as the matrix; β-type titanium alloys, which have a body-centered cubic (BCC) β-phase as the matrix; and α+β-type titanium alloys, in which both the close-packed hexagonal (HCP) α-phase and the body-centered cubic (BCC) β-phase coexist. However, the type of titanium alloy according to the present invention is not particularly limited.

[0043] <Tantalum (Ta)> Tantalum (Ta) is used to make the titanium alloy in this embodiment a titanium alloy that undergoes thermoelastic martensitic transformation. Ta has the function of lowering the transformation temperature from the β phase to the α phase to a lower temperature, stabilizing the β phase at room temperature, and making it less susceptible to slip deformation (plastic deformation).

[0044] The Ta content is preferably 15-27 at%, more preferably 19-25 at%, and most preferably 22-24 at%, when the total titanium alloy is considered to be 100 atomic percent (at%).

[0045] The upper limit for the Ta content is set based on the melting point of the titanium alloy. Figure 5 is a binary phase diagram of Ta-Ti. As shown in Figure 5, if the Ta content exceeds 27%, the melting point of the titanium alloy may exceed approximately 2000K, requiring a special melting furnace and increasing production costs. In addition, there is a possibility of incomplete melting of the Ta raw material, which can lead to a decrease in the quality of the titanium alloy.

[0046] The lower limit of the Ta content is set based on the β-phase stabilization function described above and the mechanical properties of titanium alloys as materials for medical devices and biomaterials. In other words, the β-phase stabilization function decreases as the Ta content decreases, and if the Ta content is less than 15 at%, it becomes difficult to maintain the β-phase at room temperature. For this reason, if the Ta content is less than 15 at%, it becomes difficult to obtain the mechanical properties (Young's modulus, tensile strength, and elastic deformation strain) required for medical devices and biomaterials, even if tin (Sn) is added. Accordingly, the Ta content when the total titanium alloy is considered as 100 at%, is preferably 15 at% or more, more preferably 19 at% or more, and most preferably 22 at% or more.

[0047] <Tin (Sn)> Tin (Sn) has an α-phase stabilization function that increases the transformation temperature and stabilizes the α-phase. In addition, Sn has the function of suppressing the precipitation of the ω-phase, which is a factor that increases Young's modulus, and thereby enhancing the superelastic effect of titanium alloys.

[0048] The Sn content is preferably 1 to 8 at%, and more preferably 2 to 6 at%, when the total titanium alloy is considered to be 100 atomic percent (at%).

[0049] The upper limit of the Sn content is set based on the workability (cold workability) of the titanium alloy. The graph shows the results of a cold workability evaluation test for a titanium alloy (Ti-23Ta-xSn-0.26O) with a Ta content of 23 at% when the total titanium alloy is set to 100 at%. Here, x is the Sn content (at%) when the total titanium alloy is set to 100 at%. In this cold workability evaluation test, first, multiple test pieces (thickness: 1 mm, no heat treatment) were prepared with varying Sn content x (when the total titanium alloy is set to 100 at%) of 0 at%, 1.5 at%, 3 at%, 6 at%, and 9 at%. These test pieces were then cold-rolled to a thickness of 0.1 mm (processing rate 86%), and the number of cracks with a length of 1 mm or more in each test piece after cold rolling was counted. This crack counting was performed within a range of 140 mm in the rolling direction for each test piece.

[0050] As shown in Figure 6, the results of this evaluation test confirmed that when the Sn content was 9 at%, the occurrence of cracks of 1 mm or more increased sharply, meaning that the workability deteriorated sharply. Similar trends were observed when the Ta content was different. Therefore, when the total titanium alloy is considered to be 100 at%, the Sn content is preferably 8 at% or less, and more preferably 6 at% or less, in order to obtain good workability.

[0051] While there is no particular lower limit to the Sn content, in order to fully exhibit the ω-phase suppression function described above, it is preferable that the Sn content be 1 at% or more when the total titanium alloy is considered to be 100 at%.

[0052] <Oxygen (O)> Oxygen (O) has an α-phase stabilization function that increases the transformation temperature and stabilizes the α-phase. Furthermore, O has a stronger α-phase stabilization function than Sn. In addition, O has the function of constraining crystal deformation and preventing the development of shape memory and softening.

[0053] The O content is preferably 0.4 to 1.7 at% and more preferably 0.6 to 1.0 at% when the entire titanium alloy is 100 atomic % (at%). And the O content can be changed by changing the particle size of at least one of the Ti powder and the Ta powder. Although it is possible to change the O content by changing the particle size of the Sn powder, since the content of the Sn powder is small in this embodiment, it is difficult to affect the O content in the titanium alloy even if the particle size of the Sn powder is changed.

[0054] <Regarding the upper limit of the O content (cold working evaluation)> The upper limit value of the O content is set based on the workability (cold workability) of the titanium alloy. If the O content is made too high, the titanium alloy becomes too hard due to the function of preventing O softening, and the workability deteriorates. FIG. 3 is a table showing the results of a cold working evaluation test for a titanium alloy (Ti-23.4Ta-3.4Sn-xO) in which the Ta content is 23.4 at% and the Sn content is 3.4 at% when the entire titanium alloy is 100 at%. Here, x is the O content (at%) when the entire titanium alloy is 100 at%.

[0055] In this cold working evaluation test, first, a plurality of test pieces (round wire shape with a diameter of φ10 mm, without heat treatment) were prepared in which the O content x when the entire titanium alloy (Ti-23.4Ta-3.4Sn-xO) was 100 at% was changed to 0.26 at%, 0.59 at%, 0.75 at%, 0.92 at%, 1.14 at%, 1.4 at% and 1.59 at%. Rotary forging was performed on these test pieces. At this time, each test piece was evaluated as to how much the working rate could be forged by rotary forging.

[0056] As shown in Fig. 7, as a result of this evaluation test, it was confirmed that there is no problem even if rotary forging is performed so that the processing rate of the test piece with an O content of 0.26 to 1.14 at% is 75% or more. For the test piece with an O content of 1.4 at%, there was no problem even when rotary forging was performed so that the processing rate was 50 to 75%, but cracks occurred when the processing rate exceeded 75%. For the test piece with an O content of 1.59 at%, cracks occurred when rotary forging was performed so that the processing rate exceeded 50%. Therefore, in order to obtain good workability, the O content when the entire titanium alloy is 100 at% is preferably 1.7 at% or less, more preferably 1.4 at% or less, and still more preferably 1.2 at% or less.

[0057] <Regarding the lower limit of the O content (evaluation of the structure of the titanium alloy)> The lower limit value of the O content is set particularly based on mechanical properties. That is, in conventional titanium alloys, there is a problem that the β phase is abundant and deformation occurs with a small force, so 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 having a function of restraining crystal deformation and increasing the strength of the alloy to prevent softening is precipitated. As shown in Figs. 4(B) and (C), when the titanium alloy in the present embodiment is subjected to aging treatment after heat treatment, equiaxed α phase is precipitated. However, as already described, if the O content in the titanium alloy is not sufficient, Ta as a β-stable element functions rather than O as an α-stable element, and the equiaxed α phase hardly precipitates even after aging treatment, and aging treatment lasting for several days may be required for the precipitation of the equiaxed α phase. And when the O content is less than 0.4 at%, as shown in Fig. 4(A), the precipitation amount of the equiaxed α phase is not sufficient even after aging treatment for about 2 hours, so it is difficult to maintain the shape after forming. Therefore, the O content 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 (see Fig. 4(B)).

[0058] The titanium alloy according to this embodiment exhibits extremely low elution of metal ions of its constituent elements, Ti, Ta, and Sn, as well as excellent corrosion resistance, low cytotoxicity, high biocompatibility, and is a non-magnetic material that is not easily magnetized by external magnetic fields, thus posing an extremely low risk of adverse effects on medical devices (such as MRI) that are sensitive to magnetism. It also possesses high elasticity, moderate rigidity, and high workability. In other words, the titanium alloy according to this embodiment has lower cytotoxicity and superior magnetic properties, corrosion resistance, mechanical properties, and workability compared to conventional titanium alloys. For this reason, it is suitable for medical devices such as guide wires, delivery wires, stents, aneurysm embolization coils, or venous filters in the catheter field, or for dental devices such as cleansers, reamers, files, or orthodontic wires, and for orthopedic devices such as artificial bones.

[0059] Furthermore, the method for manufacturing titanium alloys according to the present invention is not limited to the embodiments described above. For example, a powder composed of vanadium (Va) or niobium (Nb), which are other elements of the vanadium (Va) group, may be used together with or instead of tantalum (Ta) powder. In other words, the composition of the titanium alloy may include vanadium (Va) or niobium (Nb), which are other elements of the vanadium (Va) group, together with or instead of tantalum (Ta). The titanium alloy obtained by this manufacturing method has extremely stable quality. Incidentally, since vanadium (Va) or niobium (Nb), like tantalum, have high melting points, solid-phase diffusion bonding alone tends to result in an uneven internal composition of the titanium alloy, making it difficult to guarantee the quality of metal parts after cold working.

[0060] However, the specific gravities of Va, Nb, and Ta are 5.96 (g / cm³), 8.40 (g / cm³), and 16.60 (g / cm³), respectively, while the specific gravity of titanium is 4.5 (g / cm³). In other words, the specific gravity of Va is only slightly greater than that of titanium, but the specific gravities of Nb and Ta are more than twice as great as those of titanium. Therefore, it is presumed that Nb and Ta will not diffuse uniformly to a greater extent than Va during the solidification process. As a result, Nb, like Ta, may end up with a distribution similar to that shown in Figure 3 during the solidification process. Consequently, it can be said that homogenization during the dissolution process is particularly important for Nb and Ta compared to Va.

[0061] It should be noted that the titanium alloy according to the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the present invention. For example, conventionally known methods can be used to form medical guide wires, delivery wires, stents, clips, aneurysm embolization coils or venous filters, or dental cleansers, reamers, files or orthodontic wires, etc., from the titanium alloy according to the present invention, such as wire drawing, drawing, casting, forging, and press working. [Examples]

[0062] Next, examples of the titanium alloy according to the present invention will be described.

[0063] <Tensile Test 1> The inventors of the present invention performed tensile tests on test specimen T1 according to Example 1 and test specimen H1 according to Comparative Example 1, both prepared using titanium alloys according to embodiments of the present invention with varying oxygen content. Figure 8(A) is a table showing the compositions of test specimens T1 and H1 to be subjected to tensile testing. Test specimens T1 and H1 are round wires with a diameter of φ0.406 mm, formed by cold working (wire drawing) with a processing rate of 75%. Test specimen H1 according to Comparative Example 1 was prepared using a titanium alloy with the composition Ti-23Ta-3Sn-0.25O, and has a low oxygen content. Test specimen T1 according to Example 1 was prepared using a titanium alloy with the composition Ti-23Ta-3Sn-0.8O. The titanium alloys constituting test specimens T1 and H1 were heat-treated at 890°C for 1 minute, and no aging treatment was performed. Tensile tests were performed on the above test specimens T1 and H1 using a tensile testing machine. The measurement conditions were a distance of 50 mm between measurement points and a tensile speed of 2 mm / min.

[0064] Figure 8(B) shows the stress-strain diagrams obtained as a result of tensile tests performed on specimens T1 and H1. Up to a stress of approximately 200 MPa, specimens T1 and H1 deform in a manner that produces similar strains. At approximately 200 MPa, the graph has an inflection point K1. As shown in Figure 8(B), in specimen H1, the slope of the graph becomes considerably gentler after the inflection point K1 compared to the previous slope, suggesting that there is a yield region somewhere along the way (see the dotted circle area in Figure 8(B)). On the other hand, in specimen T1, as shown in Figure 8(B), the slope of the graph becomes gentler after the inflection point K1 compared to the previous slope, similar to specimen H1, but the slope of the graph is steeper compared to that of specimen H1 (see the dotted circle area in Figure 8(B)). In other words, regardless of whether or not aging treatment is performed, the test piece T1 of Example 1, which has a high O content, has harder (less yielding) material properties than the test piece H1 of Comparative Example 1, and can be said to stabilize the shape of the molded product.

[0065] <Tensile Test 2> Figure 9(A) is a stress-strain diagram obtained as a result of a tensile test in which repeated stress-strain was applied to specimen H1 of Comparative Example 1 under the same measurement conditions as Tensile Test 1. Figure 9(B) is a stress-strain diagram obtained as a result of a tensile test in which repeated stress-strain was applied to specimen T1 of Example 1 under the same measurement conditions as Tensile Test 1. Figure 9(C) is a superimposed view of the stress-strain diagrams of Figures 9(A) and (B). As is clear from Figure 9(C), when specimen H1 is subjected to a tensile stress of slightly less than 500 MPa and strained by about 2%, and then unloaded, a permanent strain of about 0.35% remains. On the other hand, when specimen T1 is subjected to a tensile stress of slightly less than 500 MPa and strained by about 2%, and then unloaded, only a permanent strain of about 0.2% remains. As a result, it was confirmed that specimen T1 of Example 1, which had an increased O content, had a higher elastic limit than specimen H1 of Comparative Example 1. [Examples]

[0066] <Tensile Test 3> Furthermore, the inventors of the present invention performed tensile tests on test specimen T2 according to Example 2 and test specimen H2 according to Comparative Example 2, both prepared using titanium alloys according to embodiments of the present invention with varying oxygen content. Figure 10(A) is a table showing the composition of test specimens T2 and H2 that were subjected to tensile testing. The composition of the titanium alloys constituting test specimens T2 and H2 is obtained by adding an additional 1 hour of aging treatment at 300°C to the titanium alloys constituting test specimen T1 of Example 1 and test specimen H2 of Comparative Example 1. Tensile tests were performed on the above test specimens T2 and H2 using a tensile testing machine. The measurement conditions were a distance between test points of 50 mm and a tensile speed of 2 mm / min.

[0067] Figure 10(B) shows the stress-strain diagrams obtained as a result of tensile tests performed on specimens T2 and H2. Up to a stress of approximately 200 MPa, specimens T2 and H2 deform in a manner that produces similar strains. At approximately 200 MPa, the graph has an inflection point K2. As shown in Figure 10(B), for specimen H2, the slope of the graph becomes considerably gentler after the inflection point K2 compared to the previous slope (see the dotted circle area in Figure 10(B)). On the other hand, for specimen T2, as shown in Figure 10(B), the slope of the graph becomes gentler after the inflection point K2 compared to the previous slope, similar to specimen H2, but the slope of the graph is steeper compared to that of specimen H2 (see the dotted circle area in Figure 10(B)). In other words, even after aging treatment, specimen T2 has material properties that make it harder (less prone to yielding) than specimen H2, and it can be said that it can stabilize the shape of the molded product.

[0068] Furthermore, comparing test specimens T2,H2 with test specimens T1,H1, the slope of the graph after the inflection point is steeper for test specimens T2,H2 than for test specimens T1,H1. This is because the titanium alloy that has undergone aging treatment contains more equiaxed α phases compared to the titanium alloy that has not undergone aging treatment, and therefore possesses the properties of a harder metal. As a result, the titanium alloy of this embodiment that has undergone aging treatment is easier to form after cold working.

[0069] Furthermore, comparing the results of tensile test 1 of specimen T1 in Example 1 (see Figure 8(B)) with the results of tensile test 3 of specimen T2 in Example 2 (see Figure 10(B)), as shown in Figure 12(A), up to the stress interval where the graphs intersect, which is slightly less than 800 MPa, specimen T2 exhibits less strain than specimen T1 even when the same stress is applied. Also, after the stress in specimens T1 and T2 reaches its maximum value (tensile strength), the strain increases at a nearly constant stress (tensile strength) for both specimens T1 and T2. Incidentally, the maximum stress (tensile strength) of specimen T1 is approximately 870 MPa, and the maximum stress (tensile strength) of specimen T2 is approximately 840 MPa. The strain leading to fracture in specimen T2 is approximately 1.2 times greater than that of specimen T1. These results suggest that titanium alloys subjected to aging treatment exhibit greater equiaxed α-phase precipitation and harder properties, as well as improved ductility, compared to titanium alloys that have not undergone aging treatment.

[0070] <Tensile Test 4> Figure 11(A) is the stress-strain diagram obtained from a tensile test in which repeated stress-strain was applied to specimen H2 under the same measurement conditions as in tensile test 3. Figure 11(B) is the stress-strain diagram obtained from a tensile test in which repeated stress-strain was applied to specimen T2 under the same measurement conditions as in tensile test 3. Figure 11(C) is a superimposed view of the stress-strain diagrams of Figures 11(A) and (B). As is clear from Figure 11(C), when specimen H2 is unloaded after being strained from 0 to 2%, a permanent strain of about 0.2% remains. On the other hand, when specimen T2 is similarly strained from 0 to 2% and then unloaded, only a permanent strain of slightly less than 0.1% remains. As a result, it was confirmed that specimen T2, with an increased O content, has a higher elastic limit than specimen H2.

[0071] Furthermore, comparing the results of tensile test 2 of specimen T1 in Example 1 (see Figure 9(B)) with the results of tensile test 4 of specimen T2 in Example 2 (see Figure 11(B)), as shown in Figure 12(B), for example, specimen T1, which has not undergone aging treatment, exhibits a strain of 0.2% when subjected to a tensile stress of approximately 500 MPa and deformed by approximately 2%, followed by unloading. However, specimen T2, which has undergone aging treatment, exhibits a strain of slightly less than 0.1% when subjected to a tensile stress of approximately 600 MPa and deformed by approximately 2%, followed by unloading. In other words, the titanium alloy that has undergone aging treatment has a higher elastic limit than the titanium alloy that has not undergone aging treatment. [Examples]

[0072] <Vickers hardness test> Furthermore, the inventors of the present invention performed Vickers hardness tests on test specimen T3 of Example 3-1 and test specimen T4 of Example 3-2, which were prepared using titanium alloys according to embodiments of the present invention with varying oxygen content. In this Vickers hardness test, 10 measurement points were used, and a load of 0.1 (N) was applied to each measurement point. A test specimen H3 of Comparative Example 3 was also prepared and subjected to a similar Vickers hardness test.

[0073] Figure 13(A) is a table showing the compositions of the test specimens T3, T4, and H3 used in the Vickers hardness test. Test specimens T3, T4, and H3 are round wires with a diameter of φ0.517 mm. Test specimen H3 is made from a titanium alloy with the composition Ti-23Ta-3Sn-0.25O, and has a low oxygen content. Test specimen T3 is made from a titanium alloy with the composition Ti-23Ta-3Sn-0.6O, and test specimen T4 is made from a titanium alloy with the composition Ti-23Ta-3Sn-0.8O. Test specimens T3, T4, and H3 were prepared both without heat treatment and after heat treatment at 450°C, 500°C, 550°C, 650°C, 700°C, and 750°C for 30 minutes.

[0074] The results of this Vickers hardness test are shown in Figure 13(B). As shown in Figure 13(B), up to a heat treatment temperature of 550°C, there was no significant change in test specimens T3, T4, and H3 due to heat treatment. On the other hand, at heat treatment temperatures of 650°C or higher, it was confirmed that the hardness of the titanium alloy tended to increase as the oxygen content increased. In other words, when the oxygen content is increased, the heat treatment temperature is preferably, for example, 600°C to 1000°C, and more preferably 700°C to 900°C.

[0075] The above tensile tests 1 through 4 and Vickers hardness tests confirmed that increasing the oxygen content improved the elastic limit and material strength. As a result, it was found that moderately increasing the oxygen content results in a titanium alloy with appropriate hardness and elastic limit that is easy to process.

[0076] Furthermore, the titanium alloy and method for manufacturing the titanium alloy of the present invention are not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the present invention. [Industrial applicability]

[0077] The titanium alloy of the present invention can be used in the catheter field, such as in medical guide wires, delivery wires, stents, clips, aneurysm embolization coils, or venous filters; in the dental field, such as in dental cleansers, reamers, files, or orthodontic wires; and in the orthopedic field, such as in artificial bone. [Explanation of Symbols]

[0078] 1 HIP device 2 HIP container 3 HIP furnace 3A Insulation Section 3B Gas introduction passage 4 Heater 5 Mixed powder 6 Consumable electrode 8. Arc melting furnace 9 rods 10 molten metal pool 11 ingots

Claims

1. At a minimum, a mixing step of mixing titanium powder, which mainly consists of titanium (Ti), and vanadium (Va) group element powder, which mainly consists of vanadium (Va) group elements, to obtain a mixed powder, A solidification step is to obtain a solidified body by heating the mixed powder mixed in the mixing step and causing solid-phase diffusion bonding, A melting step in which the solidified body is heated and melted to produce a titanium alloy, A heat treatment step involves heat treatment of the titanium alloy produced in the melting step, A aging treatment step in which the heat-treated titanium alloy is subjected to aging treatment, Equipped with, The mixed powder in the mixing step includes tantalum powder (Ta) and tin powder (Sn) as the group Va powder, and titanium powder (Ti). The titanium alloy that has undergone the aforementioned melting process, when the total volume is 100 atomic percent (at%), 15-27 at% tantalum (Ta), 1-8 at% tin (Sn), 0.4 to 1.7 at% oxygen (O), The remainder consists of titanium (Ti) and unavoidable impurities. The titanium alloy that has undergone the aforementioned aging treatment process has an equiaxed α phase, The above is characterized in that the average particle size of the equiaxed α phase is in the range of 0.05 μm to 1.0 μm. A method for manufacturing titanium alloys.

2. At a minimum, a mixing step of mixing titanium powder, which mainly consists of titanium (Ti), and vanadium (Va) group element powder, which mainly consists of vanadium (Va) group elements, to obtain a mixed powder, A solidification step is to obtain a solidified body by heating the mixed powder mixed in the mixing step and causing solid-phase diffusion bonding, A melting step in which the solidified body is heated and melted to produce a titanium alloy, A heat treatment step involves heat treatment of the titanium alloy produced in the melting step, A aging treatment step in which the heat-treated titanium alloy is subjected to aging treatment, Equipped with, The mixed powder in the mixing step includes tantalum powder (Ta) and tin powder (Sn) as the group Va powder, and titanium powder (Ti). The titanium alloy that has undergone the aforementioned melting process, when the total volume is 100 atomic percent (at%), 15-27 at% tantalum (Ta), 1-8 at% tin (Sn), 0.4 to 1.7 at% oxygen (O), The remainder consists of titanium (Ti) and unavoidable impurities. The titanium alloy that has undergone the aforementioned aging treatment process has an equiaxed α phase, The titanium alloy is characterized in that the area occupancy rate of the equiaxed α phase per unit area in the cross-section is in the range of 0.1% to 20%. A method for manufacturing titanium alloys.

3. In the heat treatment step, the titanium alloy is heat-treated at 600°C or higher. The aging treatment process is characterized by performing an aging treatment on the titanium alloy at a temperature of 550°C or lower. A method for producing a titanium alloy according to claim 1 or 2.

4. In the heat treatment step, the titanium alloy is heat-treated at a temperature of 1000°C or lower. The aging treatment process is characterized by performing an aging treatment on the titanium alloy at a temperature of 200°C or higher. A method for producing a titanium alloy according to claim 3.

5. The solidification step is characterized by heating the mixed powder at a temperature between 900 and 1400°C to cause solid-phase diffusion bonding. A method for producing a titanium alloy according to claim 1 or 2.

6. The solidification process is characterized by placing the mixed powder under vacuum and causing solid-phase diffusion bonding by heating and pressurizing. A method for producing a titanium alloy according to claim 1 or 2.

7. The dissolution step is characterized by dissolving the solidified body by a vacuum arc remelting method or a cold crucible induction dissolution method. A method for producing a titanium alloy according to claim 1 or 2.

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