Foil treatment method, foil producing method, and foil

Abstract

To provide a method for treating a titanium alloy foil, which can control the number of crystal grains aligned in the thickness direction of the titanium alloy foil.SOLUTION: A method for treating a foil comprises: a recrystallization heating step in which a foil made of a titanium alloy containing tantalum is heated under vacuum or in an inert gas atmosphere to recrystallize the foil's structure; and a foil treatment cooling step in which, after the recrystallization heating step, the foil is cooled under vacuum or in an inert gas atmosphere by a cooling rate of at least -150°C per 10 minutes, within a range up to 600°C under vacuum or in an inert gas atmosphere to suppress growth of crystal grains in the foil's structure resulting from the recrystallization. The titanium alloy contains, with the whole defined as 100 atom%, 15 to 27 atom% of tantalum, 1 to 8 atom% of tin, and 0.4 to 1.7 atom% of oxygen, with the remainder comprising titanium and inevitable impurities.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for treating a foil, a method for manufacturing a foil, and a foil.

Background Art

[0002] As a method for manufacturing a titanium foil, for example, a method for manufacturing a titanium foil from an electrodeposited titanium foil obtained by an electrochemical reaction in a molten salt bath has been proposed (see, for example, Patent Document 1). The method for manufacturing a titanium foil described in Patent Document 1 includes a cold rolling step of cold rolling an electrodeposited titanium foil obtained by an electrochemical reaction in a molten salt bath, and a finishing treatment step of performing washing and / or annealing. In molten salt electrolysis, crystal grains grow sequentially on the electrode. As a result, in Patent Document 1, it has been confirmed that in an electrodeposited titanium foil having a thickness of 190 μm, about 3 to 4 crystal grains are arranged in the thickness direction of the electrodeposited titanium foil.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when it is desired to suppress the number of crystal grains in the thickness direction of the foil within a desired range, in the method for manufacturing a titanium foil described in Patent Document 1, since the electrodeposited titanium foil on which crystal grains have grown sequentially on the electrode is only cold-rolled and annealed thereafter, it is difficult to control the number of crystal grains arranged in the thickness direction of the titanium foil.

[0005] In view of such circumstances, the present invention aims to provide a method for treating a titanium alloy foil, a method for manufacturing a titanium alloy foil, and a foil capable of controlling the number of crystal grains arranged in the thickness direction of the titanium alloy foil.

Means for Solving the Problems

[0006] The foil processing method of the present invention includes a recrystallization heating step of heating a foil made of a titanium alloy containing tantalum under vacuum or in an atmosphere of an inert gas to recrystallize the structure of the foil, and after the recrystallization heating step, cooling the foil at a cooling rate of at least -150 °C per minute in the range until the temperature of the foil reaches 600 °C under vacuum or in an atmosphere of an inert gas, so as to suppress the growth of crystal grains of the structure of the foil accompanying the recrystallization, and a foil processing cooling step. It is characterized by comprising the above.

[0007] The foil processing method of the present invention includes a recrystallization heating step of heating a foil made of a titanium alloy containing tantalum under vacuum or in an atmosphere of an inert gas to recrystallize the structure of the foil, and after the recrystallization heating step, cooling the foil by forced cooling to lower the temperature of the foil faster than in the case of natural cooling under vacuum or in an atmosphere of an inert gas, so as to suppress the growth of crystal grains of the structure of the foil accompanying the recrystallization, and a foil processing cooling step. It is characterized by comprising the above.

[0008] In the foil processing method of the present invention, when the total is 100 atomic%, the titanium alloy contains 15 atomic% to 27 atomic% of tantalum, 1 atomic% to 8 atomic% of tin, and 0.4 atomic% to 1.7 atomic% of oxygen, and the balance is composed of titanium and unavoidable impurities. It is characterized by the above.

[0009] In the foil processing method of the present invention, the degree of vacuum under the vacuum is 1×10 -2 (Pa) or less. It is characterized by the above.

[0010] In the foil processing method of the present invention, the heating temperature of the foil in the recrystallization heating step is in the range of 700 to 900 °C. It is characterized by the above.

[0011] In the method for treating a foil according to the present invention, the recrystallization heating step is performed in a furnace having a housing portion capable of housing the foil, a vacuum generating portion for evacuating the inside of the housing portion, and a heating portion for heating the housing portion. The foil treatment cooling step is characterized by cooling the foil by externally cooling the housing portion that houses the foil under an atmosphere of an inert gas or under vacuum.

[0012] In the method for treating a foil according to the present invention, the ratio of the α-phase contained in the foil after the foil treatment cooling step is 10% or less, and the ratio of the β-phase is 90% or more.

[0013] In the method for treating a foil according to the present invention, by adjusting the heating temperature in the recrystallization heating step, the average particle diameter by area weighting of crystal grains contained in the foil or the number of crystal grains arranged in the thickness direction of the foil is controlled.

[0014] The method for manufacturing a foil according to the present invention includes a foil forming step of processing a titanium alloy material made of a titanium alloy containing tantalum to form a foil, and a foil treatment step of performing a treatment on the foil. The foil forming step includes a rolling step of rolling the titanium alloy material into a foil, an annealing step of heating the titanium alloy material that has undergone the rolling step at an annealing temperature and annealing it, and a foil forming cooling step of cooling the titanium alloy material that has undergone the annealing step. The foil treatment step includes a recrystallization heating step of heating the foil under vacuum or in an atmosphere of an inert gas to recrystallize the structure of the foil, and after the recrystallization heating step, cooling the foil at a cooling rate equal to or higher than a cooling rate of -150°C per minute in the range until the temperature of the foil reaches 600°C under vacuum or in an atmosphere of an inert gas to suppress the growth of crystal grains of the structure of the foil accompanying the recrystallization. Note that the rolling step refers to the one performed last in the foil forming step.

[0015] The method for manufacturing a foil according to the present invention includes a foil forming step of processing a titanium alloy material made of a titanium alloy containing tantalum to form a foil, and a foil processing step of performing a process on the foil. The foil forming step includes a rolling step of rolling the titanium alloy material into a foil, an annealing step of heating the titanium alloy material that has undergone the rolling step at an annealing temperature and annealing it, and a foil forming cooling step of cooling the titanium alloy material that has undergone the annealing step. The foil processing step includes a recrystallization heating step of heating the foil under vacuum or in an atmosphere of an inert gas to recrystallize the structure of the foil, and a foil processing cooling step of cooling the foil by forced cooling to lower the temperature of the foil faster than when it is naturally cooled under vacuum or in an atmosphere of an inert gas after the recrystallization heating step, so as to suppress the growth of crystal grains of the structure of the foil accompanying the recrystallization.

[0016] In the method for manufacturing a foil according to the present invention, the titanium alloy contains 15 atomic% to 27 atomic% of tantalum, 1 atomic% to 8 atomic% of tin, and 0.4 atomic% to 1.7 atomic% of oxygen when the total is 100 atomic%, and the balance is composed of titanium and unavoidable impurities.

[0017] In the method for manufacturing a foil according to the present invention, the foil forming step has a processing step of performing a processing treatment on the titanium alloy material at least once before the rolling step. The processing step includes a second rolling step of rolling the titanium alloy material to reduce the thickness of the titanium alloy material, a second annealing step of heating the titanium alloy material that has undergone the second rolling step at an annealing temperature and annealing it, and a second foil forming cooling step of cooling the titanium alloy material that has undergone the second annealing step. Here, the second rolling step refers to the one performed before the finally performed rolling step. Also, the second annealing step refers to the one performed after the second rolling step in one processing step. Also, the second foil forming cooling step refers to the one performed before the foil forming cooling step.

[0018] In the method for manufacturing the foil of the present invention, the average particle diameter based on the area weighted average of the crystal grains contained in the foil or the number of crystal grains arranged in the thickness direction of the foil is controlled by adjusting the rolling reduction rate in the rolling step.

[0019] The foil of the present invention is a foil made of a titanium alloy. When the whole is 100 atomic%, the titanium alloy contains 15 atomic% to 27 atomic% of tantalum, 1 atomic% to 8 atomic% of tin, and 0.4 atomic% to 1.7 atomic% of oxygen, and the balance is composed of titanium and unavoidable impurities. The average particle diameter based on the area weighted average of the crystal grains contained in itself is in the range of 8.7 μm or more and 16.5 μm or less, the ratio of the α-phase contained in itself is 10% or less, and the ratio of the β-phase is 90% or more.

Advantages of the Invention

[0020] According to the method for manufacturing the foil of the present invention, it is possible to achieve an excellent effect of controlling the size of the crystal grains of the foil.

Brief Description of the Drawings

[0021]

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Embodiments for Carrying Out the Invention

[0022] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0023] <Method for Manufacturing Foil> The method for manufacturing a foil in this embodiment manufactures a foil from a titanium alloy material. As shown in FIG. 1, it includes a foil forming step, a cutting step, and a foil treatment step. Since the foil is made of a titanium alloy, it may also be called a titanium alloy foil.

[0024] <Titanium Alloy> First, the titanium alloy that constitutes the titanium alloy material will be described. The titanium alloy contains at least titanium (Ti) and tantalum (Ta). However, the titanium alloy may further contain elements other than Ti and Ta. Examples of elements other than Ti and Ta include tin (Sn). Specifically, when the total is 100 atomic percent (at%), the titanium alloy preferably contains 15 at% or more and 27 at% or less of Ta, 0 at% or more and 8 at% or less of Sn, and 0.4 at% or more and 1.7 at% or less of oxygen (O), and the balance consists of Ti and unavoidable impurities. Note that the content ratio of the remaining Ti is not particularly limited, and it is sufficient that Ti is the most abundant element among the contained elements when considered in terms of atomic ratio. Such a titanium alloy can obtain better mechanical properties, that is, high tensile strength, low Young's modulus, and appropriate elastic limit, and can also obtain high biocompatibility. Incidentally, the at% notation represents atomic percent, and in the following, the at% notation is used to represent the atomic percent of the corresponding element when the entire corresponding titanium alloy is 100 atomic percent (at%). Also, in the following, the numerical values attached to the element notations of Ta, Sn, and O representing the composition of the titanium alloy (see the parentheses immediately following the titanium alloy below) represent the atomic percent (at%) numerical values of each element (Ta, Sn, O) when the entire titanium alloy is 100 atomic percent (at%).

[0025] Also, titanium alloys are roughly classified into three types: α-type titanium alloys with a hexagonal close-packed (HCP) α-phase as the matrix phase, β-type titanium alloys with a body-centered cubic (BCC) β-phase as the matrix phase, and α + β-type titanium alloys in which a hexagonal close-packed (HCP) α-phase and a body-centered cubic (BCC) β-phase coexist. However, the type of titanium alloy according to the present invention is not particularly limited.

[0026] <tantalum (Ta)> Ta makes the titanium alloy in the present embodiment a titanium alloy that undergoes thermoelastic martensitic transformation. Ta has a function of lowering the transformation temperature from the β-phase to the α-phase to the low temperature side, stabilizing the β-phase at room temperature, and making it difficult to cause slip deformation (plastic deformation).

[0027] The upper limit value of the Ta content is set based on the melting point of the titanium alloy. Figure 2 is a binary phase diagram of Ta-Ti. As shown in Figure 2, when the Ta content exceeds 27 atomic %, the melting point of the titanium alloy may be 2000 K or higher, which requires a special melting furnace and increases the production cost. In addition, since the melting of the Ta raw material may be incomplete, the quality of the titanium alloy will deteriorate.

[0028] The lower limit value of the Ta content is set based on the above-mentioned β-phase stabilization function and the mechanical properties of the titanium alloy as a material for medical devices and biological materials. That is, the β-phase stabilization function decreases as the Ta content decreases. When the Ta content is less than 15 atomic %, it becomes difficult to maintain the β-phase to room temperature. For this reason, when the Ta content is less than 15 atomic %, it is difficult to obtain the mechanical properties (Young's modulus, tensile strength, and elastic deformation strain) required for materials for medical devices and biological materials even if Sn is added. Therefore, the Ta content when the entire titanium alloy is 100 atomic % is preferably 15 atomic % or more, more preferably 19 atomic % or more, and most preferably 22 atomic % or more.

[0029] From the above, the Ta content is preferably 15 to 27 atomic %, more preferably 19 to 25 atomic %, and most preferably 22 to 24 atomic % when the entire titanium alloy is 100 atomic % (atomic %).

[0030] <Tin (Sn)> Sn has an α-phase stabilization function that raises the transformation temperature and stabilizes the α-phase. In addition, Sn has a function of suppressing the precipitation of the ω-phase, which is a factor in increasing the Young's modulus, and enhancing the superelastic effect of the titanium alloy.

[0031] The upper limit of the Sn content is set based on the workability (cold workability) of the titanium alloy. Figure 3 is a graph showing the results of a cold workability evaluation test for a titanium alloy (Ti-23Ta-xSn―0.5O) with a Ta content of 23 atomic % when the total titanium alloy is 100 atomic %. Here, x is the Sn content (atomic %) when the total titanium alloy is 100 atomic %. In this cold workability evaluation test, first, a plurality of test pieces (thickness: 1 mm, no heat treatment) with the Sn content x changed to 0 atomic %, 1.5 atomic %, 3 atomic %, 6 atomic %, and 9 atomic % when the total titanium alloy is 100 atomic % were prepared. Then, these test pieces were cold-rolled to a thickness of 0.1 mm (working 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 of each test piece. Note that the working rate refers to the percentage (%) obtained by dividing the difference between the cross-sectional area of the material before processing and the cross-sectional area after processing by the cross-sectional area of the material before processing in cold plastic processing such as wire drawing and rolling.

[0032] As shown in Figure 3, as a result of this evaluation test, it was confirmed that when the Sn content is 9 atomic %, the occurrence of cracks of 1 mm or more increases rapidly, that is, the workability deteriorates rapidly. Also, even when the Ta content is different, the same tendency was shown in the results. Therefore, the Sn content when the total titanium alloy is 100 atomic % is preferably 8 atomic % or less, and more preferably 6 atomic % or less in order to obtain good workability.

[0033] Note that the lower limit of the Sn content is not particularly limited, but it may be 0 atomic % as described above. This is because even if Sn is not added, a titanium alloy having the required mechanical properties (Young's modulus, tensile strength, and elastic deformation strain) can be obtained as long as the Ta content is 15 atomic % or more.

[0034] However, in order to further improve the mechanical properties, it is preferable to add Sn to the titanium alloy. For example, from the perspective of the superelastic effect of the titanium alloy, Sn has the function of suppressing the precipitation of the ω phase, which is a factor increasing the Young's modulus, and enhancing the superelastic effect of the titanium alloy. This superelasticity enables flexible response to unintended deformations. Therefore, it is preferable to add Sn to the titanium alloy. In addition, in order to fully exert the above ω phase suppression function, the content of Sn is preferably 1 atomic % or more when the total titanium alloy is 100 atomic %.

[0035] From the above, the content of Sn is preferably 1 to 8 atomic %, more preferably 2 to 6 atomic % when the total titanium alloy is 100 atomic % (at%).

[0036] Moreover, the above titanium alloy containing Sn has extremely low elution amounts of metal ions of its constituent elements Ti, Ta, and Sn, exhibits excellent corrosion resistance, low cytotoxicity, high biocompatibility, and is a non-magnetic material that is hardly magnetized by an external magnetic field and has an extremely low risk of affecting medical devices (such as MRI) that dislike magnetism. It is an alloy with high elasticity, appropriate rigidity, and high workability. That is, the above titanium alloy containing Sn has lower cytotoxicity compared to conventional titanium alloys and has excellent magnetic properties, corrosion resistance, mechanical properties, and workability.

[0037] <Oxygen (O)> Oxygen (O) has an α-phase stabilizing function of increasing the transformation temperature and stabilizing the α phase. And 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 manifestation and softening of shape memory.

[0038] The content of O is preferably 0.4 to 1.7 at% and more preferably 0.6 to 1.0 at% when the total amount of the titanium alloy is 100 atomic%. And the content of O 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 content of O 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 content of O in the titanium alloy even if the particle size of the Sn powder is changed.

[0039] <Method for manufacturing titanium alloy> Next, with reference to FIGS. 4 and 5, the method for manufacturing a titanium alloy material in an embodiment of the present invention will be described below.

[0040] <Mixing step> First, as shown in FIG. 4, 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 at a predetermined mixing ratio. In this embodiment, the Ti powder, Ta powder, and Sn powder are all assumed to have a particle size (particle diameter) that can pass through a sieve having a mesh size of 325 (mesh / inch) or less. The above Ti powder preferably contains 90% or more of Ti, more preferably 95% or more of Ti, and still more preferably 99% or more of Ti. In this case, the remaining components of the Ti powder contain components other than Ti. Also, the Ti in the above Ti powder may contain pure Ti or Ti having an oxide film. The above Ta powder preferably contains 90% or more of Ta, more preferably 95% or more of Ta, and still more preferably 99% or more of Ta. In this case, the remaining components of the Ta powder contain components other than Ta. Also, the Ta in the above Ta powder may contain pure Ta or Ta having an oxide film. The above Sn powder preferably contains 90% or more of tin (Sn), more preferably 95% or more of tin (Sn), and still more preferably 99% or more of Sn. In this case, the remaining components of the Sn powder contain components other than Sn. Also, the Sn in the above Sn powder may contain pure Sn or Sn having an oxide film.

[0041] For powders of the same weight, the number of particles constituting the powder is larger for powders with smaller particle sizes than for powders with larger particle sizes. As a result, when compared by the same weight, the surface area of the powder with a smaller particle size that reacts with oxygen is larger than that of the powder with a larger particle size. Ti powder and Ta powder are in a stable state in the atmosphere due to the oxide film. As a result, when compared by the same weight, mixing Ti powder and Ta powder with smaller particle sizes increases the O content in the titanium alloy, which is the final product, more than that of the powder with a larger particle size. Therefore, the particle sizes of Ti powder and Ta powder affect the O content in the titanium alloy, and the O content in the titanium alloy can be adjusted by appropriately selecting the particle sizes of each powder. For this reason, to provide a plurality of titanium alloys with different oxygen contents, at least one of the particle sizes of Ti powder and Ta powder may be changed. Note that if the desired oxygen content cannot be achieved only by reducing the particle size of Ti powder and / or Ta powder, since titania powder itself contains oxygen, titania powder may be additionally mixed.

[0042] For example, when the total is 100 atomic % (at%), Ti powder or titania powder, Ta powder, and Sn powder are uniformly mixed at a mixing ratio such that it consists of 15 - 27 at% Ta, 1 - 8 at% Sn, 0.4 - 1.7 at% O, and the balance is titanium (Ti) and inevitable impurities. When converted to weight %, when the total is 100 weight % (wt%), Ta becomes 40 - 56 wt%, Sn becomes 2 - 10 wt%, O becomes 0.1 - 0.3 wt% O, and the balance is Ti and inevitable impurities. For example, in the case of a titanium alloy of Ti - 23.4Ta - 3.4Sn - xO, when the total is 100 weight %, it is mixed such that Ta powder is 52 weight %, Sn powder is 5 weight %, and the rest is Ti powder or titania powder. The O content is adjusted by adjusting the particle sizes of Ti powder and Ta powder having an oxide film on the surface, or by using titania powder. Note that in this embodiment, since the content of Sn powder is small, it is presumed that the influence of Sn powder on the O content is small.

[0043] <Solidification process> Next, as shown in FIG. 4, a solidification step is performed in which a mixed powder of Ti powder or titania powder, Ta powder, and Sn powder uniformly mixed in the above mixing step (hereinafter simply referred to as the mixed powder) is solidified by solid-phase diffusion bonding of the mixed powder under vacuum. By the solidification step, the above mixed powder becomes a solid. Since the mixed powder is solid-phase diffusion bonded in a state of being placed under vacuum, it is possible to limit the entry of oxygen (O) that is not expected from the outside air into the solid. In addition, in the present embodiment, the solid refers to a material in which the mixed powder is solid-phase diffusion bonded into one mass. In the solidification step, for example, any one of normal heat treatment (for example, sintering treatment by heating), pressure and heat treatment performed simultaneously, and the like is adopted. As the pressure and heat treatment, for example, any one of hot isostatic pressing (HIP), spark isostatic pressing (SIP), and spark plasma sintering (SPS) is used, and the mixed powder is solidified by any one of them. Incidentally, HIP and SIP are isostatic (hydrostatic) pressing, and SPS is pressing with direction (axial direction pressing) using a press machine and a mold. In addition, the pressure under vacuum in which the mixed powder is placed in the present embodiment is, for example, preferably 1.0×10 -1 (Pa) or less, more preferably in the range of 1.0×10 -2 ~1.0×10 -5 (Pa), and even more preferably in the range of 1.0×10 -2 ~1.0×10 -3 (Pa).

[0044] Here, with reference to FIG. 5(A), a case where the treatment by the hot isostatic pressing method (hereinafter referred to as HIP treatment) is used in the solidification step will be described as an example. First, the above mixed powder 5 is pressure-filled into the HIP container 2. The HIP container 2 is composed of, for example, a cylindrical container with one end face side open and the other end face side closed, and a lid. The mixed powder 5 is filled while being compressed into the cylindrical container, and the cylindrical container is installed in a vacuum chamber of an electron beam device (not shown). Then, the pressure in the vacuum chamber is, for example, 1.0×10-2 ~1.0×10 -3 (Pa), the electron beam welding is carried out in a vacuum state within this range, and a lid is welded to the opening of the HIP container 2 to seal the HIP container 2. As a result, the mixed powder is disposed under vacuum inside the HIP container 2.

[0045] As the material of the HIP container 2, it is preferable to adopt a material other than Ta. However, Ta is extremely expensive and not practical for mass production. Therefore, for example, as the material of the HIP container 2, it is preferable to use a material mainly composed of Ti or iron, and more preferably a material mainly composed of iron. Incidentally, in a general HIP process, the HIP container 2 is made of the same material as the material (here Ta) with the highest melting point among the mixed powders 5.

[0046] Then, the HIP container 2 is installed inside the heat insulation part 3A of the HIP furnace 3 of the HIP apparatus 1. The HIP apparatus 1 is configured such that the inner region of the heat insulation part 3A of the HIP furnace 3 can be made into a high-temperature and high-pressure atmosphere by heating with a substantially inert gas such as argon and the heater 4. Also, the gas is supplied from the outside into 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 to become a solidified body. Since the mixed powder 5 is sealed inside the HIP container 2 in a vacuum state, it is possible to limit the entry of oxygen (O) that is not expected from the outside air into the solidified body even when the mixed powder 5 is pressurized and heated through the HIP container 2. Incidentally, immediately after the HIP treatment, the HIP container 2 and the solidified body are in a firmly bonded state. Therefore, to separate the HIP container 2 and the solidified body, the HIP container 2 and the layer where the HIP container 2 and the solidified body are mixed are cut by a machine tool. As a result, only the solidified body remains. Thereby, a cylindrical solidified body is formed.

[0047] In HIP treatment, 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 a predetermined time to obtain a solidified body. Note that the temperature inside the HIP furnace 3 may be any temperature as long as the HIP container 2 does not break or melt. As such a temperature inside the HIP furnace 3, for example, 700°C to 1600°C is preferable, 900°C to 1400°C is more preferable, and 1000°C to 1200°C is even more preferable. 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).

[0048] <Melting step> Next, as shown in FIG. 4, a melting step of melting the solidified body of the mixed powder solidified in the above solidification step is performed. By the melting step, the solidified body is melted to form an ingot of a titanium alloy. As described above, although the components of the solidified body are not uniformly diffused, by performing the melting step, each component can be uniformly melted (dissolved) to obtain an ingot of a titanium alloy in which each component is uniformly dispersed. Note that in the melting step, in order to simultaneously melt Ta, Sn, and Ti having different melting points and uniformly diffuse them, 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 step, for example, any one of a vacuum arc remelting method (VAR), an electro-slag remelting method (ESR), a vacuum induction melting method (VIM), a cold crucible induction melting method (CCIM), a plasma arc melting method (PAM), and an electron beam melting method (EBM) is used, and the solidified body is melted by any one of them.

[0049] Here, with reference to FIG. 5(B), the case of using the vacuum arc remelting method (VAR) 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 that is suspended in the arc melting furnace 8. As a result, the consumable electrode 6 is suspended and supported by the rod 9 in a state where the molten metal pool 10 is located directly below in the arc melting furnace 8. 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. Due to the high heat generated by the arc discharge, the consumable electrode 6 is heated and melted, and it accumulates below to become the titanium alloy ingot 11.

[0050] Note that after connecting the titanium alloy ingot 11 as the consumable electrode 6 to the rod 9, it may be installed in the arc melting furnace 8 as described above, and current may be passed through it again for melting. And this process can be repeated a plurality of times to enhance the reliability of the homogenization of each component, so it may be repeated further. The titanium alloy is provided as described above.

[0051] <Cold working process> Next, as shown in FIG. 4, cold working is performed on the titanium alloy ingot provided in the above melting process. By cold working the titanium alloy ingot, a titanium alloy material is formed.

[0052] <Heat treatment process> Next, as shown in FIG. 4, a heat treatment process of heat-treating the titanium alloy material provided in the above cold working process is performed. The heat treatment temperature is preferably, for example, 600°C to 1000°C, and more preferably 700°C to 900°C. Note that the heat treatment process may be omitted.

[0053] <Aging treatment process> Next, as shown in FIG. 4, an aging treatment step is performed in which the titanium alloy material heat-treated in the above heat treatment step or the titanium alloy material that has not been heat-treated after undergoing a cold working step is aged. The aging treatment temperature is preferably 200°C to 550°C, more preferably 300°C to 500°C. When the titanium alloy material in the present embodiment is subjected to the above aging treatment for a predetermined time, equiaxed α-phase and the like precipitate in the titanium alloy material. Note that the α-phase is not limited to being equiaxed, and other forms may be included.

[0054] <Foil forming step> Next, the foil forming step will be described. The foil forming step includes at least one processing step.

[0055] <Processing step> In the processing step, the titanium alloy material manufactured as described above is rolled to process it into a titanium alloy plate material with a thinner thickness (hereinafter referred to as a titanium alloy rolled material). In the first processing step, the titanium alloy material formed in a plate shape (hereinafter referred to as a titanium alloy plate material) is rolled. The initial thickness of the titanium alloy plate material is, for example, 5 mm, but it is not limited to this, and other thicknesses may be used.

[0056] The processing step may be performed once or may be repeated a plurality of times. The number of times of the processing step varies depending on the thickness of the titanium alloy plate material, the final thickness of the foil, the resistance of the titanium alloy plate material, and the like. Specifically, as shown in FIG. 1, the processing step includes a rolling step, an annealing step, and a foil forming cooling step.

[0057] <Rolling step> In the initial rolling process, the titanium alloy sheet is rolled to process it into a thinner titanium alloy rolled material. In the rolling processes after the second time, the titanium alloy rolled material that has undergone the first processing step is rolled to make the plate thickness of the titanium alloy rolled material thinner. Specifically, in each rolling process, the titanium alloy sheet 12 is rolled by one or a plurality of rolling processes by a preset reduction ratio. In the rolling process in the present embodiment, for example, a cold rolling device 20 having a pair of rolling rollers 21 and 22 as shown in FIG. 6(A) is used.

[0058] The pair of rolling rollers 21 and 22 are arranged opposite to each other, and the distance D of the gap 23 between the pair of rolling rollers 21 and 22 is configured to be changeable. Further, the cold rolling device 20 is configured to rotatably support the pair of rolling rollers 21 and 22. When the titanium alloy sheet 12 is passed through the gap 23 of the pair of rolling rollers 21 and 22 from one side of the cold rolling device 20, as shown in FIG. 6(B), the titanium alloy sheet 12 moves so as to pass through the gap 23 by the rotation of the pair of rolling rollers 21 and 22 and is sent to the opposite side of the cold rolling device 20. At this time, the passing area of the titanium alloy sheet 12 that has passed through the gap 23 is rolled by the pair of rolling rollers 21 and 22 to have a thickness corresponding to the distance D of the gap 23 between the pair of rolling rollers 21 and 22 and becomes thinner.

[0059] In one rolling process, the titanium alloy sheet 12 is passed between the pair of rolling rollers 21 and 22 once or a plurality of times while changing the distance D of the gap 23 to process it into a titanium alloy rolled material that has been rolled by a desired reduction ratio. Note that the rolling process before the last rolling process may be referred to as the second rolling process, distinguished from the last rolling process.

[0060] <Annealing Process> In the annealing process, the titanium alloy rolled material rolled in the rolling process is heated at the annealing temperature to perform annealing treatment. Specifically, the annealing process is performed on the titanium alloy rolled material rolled by a preset rolling reduction rate in one rolling process. The annealing treatment is performed by putting the titanium alloy rolled material into a furnace (not shown). Also, the annealing treatment may be performed in the atmosphere or under vacuum. The annealing treatment removes the strain and residual stress of the titanium alloy rolled material. The annealing temperature is preferably in the range of 650 to 900 °C, more preferably in the range of 680 to 800 °C, and even more preferably in the range of 700 to 750 °C, but is not limited thereto, and other temperature ranges may also be used. Note that the annealing process that is set with the second rolling process in the processing step may be referred to as the second annealing process.

[0061] <Foil forming cooling process> In the foil forming cooling process, the titanium alloy rolled material that has undergone the annealing process is cooled by leaving it for a predetermined time. Specifically, in the foil forming cooling process, for example, the heating operation of the furnace containing the titanium alloy rolled material is stopped and left (furnace cooling). The standing time for cooling is, for example, in the range of 15 to 24 hours at room temperature (for example, in the range of 10 °C to 30 °C) as an example. Note that in the foil forming cooling process, the titanium alloy rolled material may be quenched by forced cooling that reduces the temperature of the titanium alloy rolled material faster than in the case of furnace cooling (natural cooling).

[0062] <Subsequent processing steps after the second time> In the subsequent processing steps after the second time, as described above, the rolling process, the annealing process, and the foil forming cooling process are performed in order. However, the rolling reduction rate in each processing step may be different or the same.

[0063] After undergoing one or a plurality of processing steps, the titanium alloy plate becomes a foil. The thickness of the foil is, for example, 0.03 mm, but is not limited thereto, and is preferably any one of 0.01 mm or more and 0.1 mm or less, more preferably any one of 0.01 mm or more and 0.07 mm or less, and even more preferably any one of 0.02 mm or more and 0.05 mm or less.

[0064] <Cutting Process> In the cutting process, the foil is cut into a predetermined size. Here, the foil may be cut into a size that is easy to process in the foil processing step, or the foil may be cut into the shipping size. In the former case, after the foil processing step, a separate cutting step for cutting the foil into the shipping size is additionally added.

[0065] <Foil Processing Step> The foil processing step is applied to the foil formed by the foil forming step. In this sense, the foil processing step can be said to be a method of processing the foil. Specifically, as shown in FIG. 1, the foil processing step includes a recrystallization heating step and a foil processing cooling step.

[0066] <Recrystallization Heating Step> In the recrystallization heating step, the foil is heated to recrystallize the structure of the foil. In this sense, it can be said that in the recrystallization heating step, a heat treatment (recrystallization heat treatment) for recrystallization is performed on the foil. The recrystallization heating step is preferably performed in an atmosphere of an inert gas or under vacuum. Examples of the inert gas include argon, neon, helium, etc. The heating temperature here (hereinafter, the recrystallization heating temperature) is preferably in the range of 760 to 900 ° C, more preferably in the range of 750 to 850 ° C, and even more preferably in the range of 780 to 820 ° C, but is not limited thereto, and any other temperature may be used as long as it is a temperature at which the structure of the foil can be recrystallized.

[0067] A large number of processing strains occur in the foil that has undergone the foil forming step (processing step). When such a foil is heated at the recrystallization heating temperature, the processing strain becomes the nucleus of the crystal grains, and new crystal grains gradually grow. The new crystal grains grow larger as the heating time becomes longer. For this reason, the heating time in the recrystallization heating step (hereinafter, the recrystallization heating time) is preferably in the range of 30 to 100 minutes, more preferably in the range of 30 to 80 minutes, and even more preferably in the range of 30 to 60 minutes, but is not limited thereto, and any other range may be used.

[0068] Specifically, in the recrystallization heating process, as shown in FIG. 7(A), the foil 13 is accommodated in the accommodating portion 31 of the furnace 30. The accommodating portion 31 has an inlet / outlet 31A. The inlet / outlet 31A is opened and closed by an opening / closing portion 31B. When the opening / closing portion 31B is closed, the accommodating portion 31 is in a sealed state. At this time, the foil 13 is placed on the base material 32 in the accommodating portion 31. Then, the weight material 33 is placed on the foil 13. As a result, the foil 13 is sandwiched between the base material 32 and the weight material 33. The base material 32 and the weight material 33 are preferably formed in a plate shape. As shown in FIG. 7(A), one or a plurality of foils 13 and one weight material 33 may be alternately laminated, or as shown in FIG. 7(B), a plurality of foils 13 may be laminated on the base material 32, and the weight material 33 may be placed on the uppermost layer foil 13. Further, the base material 32 may be omitted, and the foil 13 may be directly installed on the bottom surface of the accommodating portion 31. In this case, the foil 13 is sandwiched between the bottom surface of the accommodating portion 31 and the weight material 33.

[0069] When performing the recrystallization heating process under vacuum, the inside of the accommodating portion 31 is evacuated by a vacuum generating portion 35. The vacuum generating portion 35 includes, for example, a pump that extracts the air inside the accommodating portion 31. In the present embodiment, the pressure (degree of vacuum) under vacuum inside the accommodating portion 31 is preferably, for example, 1.0 (Pa) or less, more preferably 1.0×10 -1 or less, and even more preferably 1.0×10 -2 or less. This is to suppress the oxidation of the foil 13.

[0070] The inside of the accommodating portion 31 under vacuum is heated by the heating portion 34 at the recrystallization heating temperature and the recrystallization heating time selected from the above ranges of the recrystallization heating temperature and the recrystallization heating time. Thereby, the foil 13 is heated under vacuum. The foil 13 is sandwiched between the base material 32 and the weight material 33 and is corrected to a straight posture. As a result, the foil 13 is prevented from warping due to heating.

[0071] As shown in Fig. 7(C), in order to ensure that the foil 13 does not warp, the base material 32 preferably has a shape and size that can contact the entire area of the plane on one side of the foil 13, and the weight material 33 preferably has a shape and size that can contact the entire area of the plane on the other side of the foil 13. In addition, the materials of the base material 32 and the weight material 33 are preferably materials that do not bond to the foil 13 by heating at the annealing temperature. As such a material, for example, molybdenum (Mo) can be cited as an example.

[0072] <Foil treatment cooling process> In the foil treatment cooling process, after the recrystallization heating process, the foil is cooled. The foil treatment cooling process is preferably carried out in an atmosphere of an inert gas or under vacuum. The cooling in the foil treatment cooling process is forced cooling that reduces the temperature of the foil faster than when furnace cooling (natural cooling). The forced cooling is preferably cooling at a cooling rate of -150 °C or more per 10 minutes in the range until the temperature of the foil reaches 600 °C. As a specific mode of forced cooling, for example, a mode of forcibly cooling the foil by blowing air with a blower can be cited as an example, but it is not limited thereto, and a mode of forcibly cooling the foil in a refrigerator or freezer where the temperature of the room is lower than room temperature may also be used.

[0073] When forcibly cooling the foil by blowing air, in the foil treatment cooling process, as shown in Figs. 7(A) and (B), air is blown from the outside of the housing part 31 into the housing part 31 in an atmosphere of an inert gas or under vacuum where the foil is housed by a blower 40 to forcibly cool the foil. When forcibly cooling the foil in a refrigerator or freezer, for example, the housing part 31 is moved to the refrigerator or freezer by a moving mechanism (not shown) that moves the housing part 31, and the foil is forcibly cooled in the refrigerator or freezer while being housed in the housing part 31. By forced cooling by blowing air or by a refrigerator or freezer, the growth of crystal grains in the structure of the foil accompanying recrystallization is suppressed. As a result, the growth of crystal grains in the structure of the foil stops at a stage of a predetermined size, and a plurality of crystal grains of an appropriate size can be provided in the structure of the foil.

[0074] Note that when the heating operation of the furnace is stopped and left without performing the foil treatment cooling process, and the foil is cooled in the furnace (naturally cooled), the growth of crystal grains does not stop at a predetermined size, and the size of each crystal grain becomes larger. Therefore, in the thickness direction of the foil, the number of crystal grains contained in the foil decreases. When the foil is cooled by furnace cooling (natural cooling), for example, in the case of the foil with a thickness of 0.03 mm in the present embodiment, in the thickness direction of the foil, the number of crystal grains contained in the foil is about 1 to 3.

[0075] On the other hand, when the foil treatment cooling process is performed instead of furnace cooling (natural cooling), the growth of crystal grains is suppressed, so the size of each crystal grain becomes smaller compared to the case of furnace cooling (natural cooling). Therefore, in the thickness direction of the foil, the number of crystal grains contained in the foil increases. When the foil is cooled by the foil treatment cooling process, for example, in the case of the foil with a thickness of 0.03 mm in the present embodiment, in the thickness direction of the foil, the number of crystal grains contained in the foil can be 5 or more.

[0076] As described above, the crystal grains of the foil grow in the recrystallization heating process, but the growth of the crystal grains can be suppressed by forced cooling in the foil treatment cooling process. Therefore, according to the foil treatment process (foil treatment method), the number of crystal grains arranged in the thickness direction of the titanium alloy foil can be controlled.

[0077] Hereinafter, the present invention will be described in more detail based on examples.

Examples

[0078] In order to verify the foil of the present invention, the inventor of the present application created the first foil to the sixth foil corresponding to the foil of the present invention and the first comparative example foil to the sixth comparative example foil as comparative examples as follows.

[0079] <Creation of the first foil to the sixth foil> First, to create the first to third foils, three titanium alloy plates with a thickness of 5 mm were subjected to a processing step five times and then a foil processing step. Specifically, in the rolling step of the first processing step, using the cold rolling apparatus 20 as shown in FIG. 6, the three titanium alloy plates were rolled with a reduction ratio of 60% to process them into three titanium alloy rolled materials with a thickness of 2 mm. The titanium alloy plate is composed of a titanium alloy with a composition of Ti-23Ta-3Sn-0.6O.

[0080] Then, in the annealing step, the three titanium alloy rolled materials with a thickness of 2 mm were placed in a furnace and heated at an annealing temperature of 700°C for 30 minutes. In the foil forming cooling step, the heating operation of the furnace containing the three titanium alloy rolled materials with a thickness of 2 mm was stopped, and the three titanium alloy rolled materials with a thickness of 2 mm were left for 24 hours.

[0081] In the rolling step of the second processing step, using the cold rolling apparatus 20, the three titanium alloy rolled materials with a thickness of 2 mm were rolled with a reduction ratio of 60% to process them into titanium alloy rolled materials with a thickness of 0.8 mm. The annealing step and the foil forming cooling step for the three titanium alloy rolled materials with a thickness of 0.8 mm are the same as those in the first time.

[0082] In the rolling step of the third processing step, using the cold rolling apparatus 20, the three titanium alloy rolled materials with a thickness of 0.8 mm were rolled with a reduction ratio of 60% to process them into three titanium alloy rolled materials with a thickness of 0.32 mm. The annealing step and the foil forming cooling step for the three titanium alloy rolled materials with a thickness of 0.32 mm are the same as those in the first time.

[0083] In the rolling step of the fourth processing step, using the cold rolling apparatus 20, the three titanium alloy rolled materials with a thickness of 0.32 mm were rolled with a reduction ratio of 62.5% to process them into three titanium alloy rolled materials with a thickness of 0.12 mm. The annealing step and the foil forming cooling step for the three titanium alloy rolled materials with a thickness of 0.12 mm are the same as those in the first time.

[0084] In the rolling process of the fifth processing step, using the cold rolling apparatus 20, three titanium alloy rolled materials with a thickness of 0.12 mm were rolled with a rolling reduction (final rolling reduction) of 75% to produce three foils of titanium alloy rolled materials with a thickness of 0.03 mm. The annealing process and the foil forming cooling process for the foils are the same as those in the first time. Each of these three foils corresponds to the first foil, the second foil, and the third foil.

[0085] In the foil processing step, the recrystallization heating temperature for the first foil was set at 780°C, the recrystallization heating temperature for the second foil was set at 800°C, the recrystallization heating temperature for the third foil was set at 820°C, and the recrystallization heating time for all was 30 minutes. Heat treatment (recrystallization heat treatment) was performed on the first to third foils in a furnace under vacuum (1.0×10 -1 (Pa)). Then, using a blower, the housing 31 of the furnace 30 was blown at 6.8 (m 3 / min) for 5 hours (foil processing cooling step) to forcibly cool the first to third foils and make the temperature inside the housing 31 of the furnace 100°C or lower. The temperature change of the second foil in which the recrystallization heating process and the foil processing cooling step were performed is shown in Fig. 9. In this blowing, the first to third foils were cooled at a cooling rate of -300°C per 10 minutes until the temperature of the first to third foils reached 600°C. Thus, the first to third foils were completed.

[0086] Similarly, to produce the fourth to sixth foils, after performing the processing step four times on three titanium alloy plates with a thickness of 5 mm, a foil processing step was performed. The processing steps up to the third time are the same as those for the first to third foils. In the rolling process of the fourth processing step, using the cold rolling apparatus 20, three titanium alloy rolled materials with a thickness of 0.32 mm were rolled with a final rolling reduction of approximately 90% to produce three foils of titanium alloy rolled materials with a thickness of 0.03 mm. The annealing process and the foil forming cooling process for the foils are the same as those in the first time for the first to third foils. Each of these three foils corresponds to the fourth foil, the fifth foil, and the sixth foil.

[0087] In the foil treatment step, the recrystallization heating temperature for the fourth foil was set at 780°C, the recrystallization heating temperature for the fifth foil was set at 800°C, and the recrystallization heating temperature for the sixth foil was set at 820°C. With a recrystallization heating time of 30 minutes for each, heat treatment (recrystallization heat treatment) was performed on the fourth to sixth foils in a furnace under vacuum (1.0×10 -1 (Pa)). Thereafter, using a blower, the housing portion 31 of the furnace 30 was blown with air at 6.8 (m 3 / min) for 5 hours to forcibly cool the fourth to sixth foils, bringing the temperature inside the housing portion 31 of the furnace to 100°C or lower. Thus, the fourth to sixth foils were completed. Note that also in this blowing, similar to the case of the first to third foils, the fourth to sixth foils were cooled at a cooling rate of -300°C per 10 minutes in the range until the temperature of the fourth to sixth foils reached 600°C.

[0088] <Creation of the first to sixth comparative example foils> Next, in order to create the first to sixth comparative example foils, a processing step was performed 6 times on three titanium alloy plates with a thickness of 5 mm, followed by the foil treatment step. Specifically, up to the 4th processing step, the content was the same as that for the first to third foils. In the 5th processing step, rolling with a rolling reduction rate of 58.3% was performed on six titanium alloy rolled materials to process them into six titanium alloy rolled materials with a thickness of 0.05 mm. In the 6th processing step, rolling with a final rolling reduction rate of 40% was performed on the six titanium alloy rolled materials to create six foils that were titanium alloy rolled materials with a thickness of 0.03 mm. Then, the annealing step and the foil forming cooling step in the 5th and 6th processing steps were the same as those for the first time for the first to third foils. Each of these six foils corresponds to the first to sixth comparative example foils.

[0089] In the foil treatment step, the recrystallization heating temperature for the first comparative example foil was 780°C, the recrystallization heating time was 30 minutes, the recrystallization heating temperature for the second comparative example foil was 800°C, the recrystallization heating time was 30 minutes, the recrystallization heating temperature for the third comparative example foil was 840°C, the recrystallization heating time was 30 minutes, the recrystallization heating temperature for the fourth comparative example foil was 780°C, the recrystallization heating time was 60 minutes, the recrystallization heating temperature for the fifth comparative example foil was 800°C, the recrystallization heating time was 60 minutes, and the recrystallization heating temperature for the sixth comparative example foil was 840°C, the recrystallization heating time was 60 minutes. Under vacuum (1.0×10 -1 (Pa)), heat treatment (recrystallization heat treatment) was performed on the first to sixth comparative example foils. Then, the heating operation of the furnace was stopped and left to stand, and each of the first to sixth comparative example foils was furnace-cooled (naturally cooled) to bring the temperature in the housing portion 31 to 100°C or lower. In furnace cooling (natural cooling), the cooling rate was such that the temperature of the first to sixth comparative example foils decreased by -100°C per 10 minutes in the range until the temperature reached 600°C.

[0090] Here, when the cold rolling apparatus 20 is used in the rolling step, as shown in FIG. 6, the length direction of the foil along the moving direction E (see FIGS. 4(A) and 4(B)) of the titanium alloy material (titanium alloy rolled material) or foil is defined as the passing side length direction A, and the direction orthogonal to both the passing length direction A and the foil thickness direction C is defined as the orthogonal direction B. Orthogonal cut surfaces V (see FIG. 8) obtained by cutting each of the first to sixth foils along the orthogonal direction B were observed at a magnification of 4000 times with an electron microscope (FE-SEM JSM7800F-Prime manufactured by JEOL Ltd.), and the photographs taken during the observation are shown in FIGS. 10 and 11.

[0091] Also, orthogonal cut surfaces V (see FIG. 8) obtained by cutting each of the first to sixth comparative example foils created as described above along the orthogonal direction B were observed at a magnification of 4000 times with an electron microscope (FE-SEM JSM7800F-Prime manufactured by JEOL Ltd.), and the photographs taken during the observation are shown in FIGS. 12 and 13.

[0092] <Comparison of crystal grains> The results of counting the number of crystal grains arranged in the thickness direction of the foil in the cross-sections of the first comparative example foil to the sixth comparative example foil shown in FIGS. 12 and 13 are shown in FIG. 14(B). The method of counting the number of crystal grains was carried out by drawing a line (refer to the dotted line) along the thickness direction C of the foil in the cross-section of the foil and counting the crystal grains on the line along the thickness direction C of the foil, as shown in FIG. 14(A). In FIG. 14(A), as an example, a cross-sectional photograph of the second comparative example foil shown in FIG. 12(B) is used.

[0093] The number of crystal grains arranged in the thickness direction of each of the first comparative example foil, the second comparative example foil, the fourth comparative example foil, and the fifth comparative example foil was 3. On the other hand, the number of crystal grains arranged in the thickness direction of each of the third comparative example foil and the sixth comparative example foil was 3 or less. From the above, it was confirmed that the number of crystal grains arranged in the thickness direction of the foil in the cross-sections of the first comparative example foil to the sixth comparative example foil was 3 or less. On the other hand, it was confirmed that at least 5 or more crystal grains were arranged in the thickness direction of the foil in the orthogonal cut surface V of the first foil to the sixth foil shown in FIGS. 10 and 11.

[0094] From the above, it can be said that for the foil that has not undergone the foil treatment cooling process, the growth of crystal grains progresses and the length of each crystal grain in the thickness direction C of the foil becomes longer, but for the foil that has undergone the foil treatment cooling process, the growth of crystal grains is suppressed and the size (length in the thickness direction of the foil) of each crystal grain in the thickness direction of the foil can be suppressed.

[0095] Also, when comparing the orthogonal cut surfaces V of the first foil to the third foil, many of the second foil and the third foil contain larger crystal grains than the first foil. Also, when comparing the orthogonal cut surfaces V of the fourth foil to the sixth foil, many of the fifth foil and the sixth foil contain larger crystal grains than the fourth foil. The first foil and the fourth foil have a recrystallization heating temperature of 780°C, while the other foils (the second foil, the third foil, the fifth foil, and the sixth foil) have a recrystallization heating temperature of 800°C or higher. It is presumed that the difference in the recrystallization heating temperature affects the size of the crystal grains. Therefore, in order to generate many crystal grains in the thickness direction of the foil, the recrystallization heating temperature is preferably less than 800°C. Conversely, in order to suppress the number of crystal grains in the thickness direction of the foil, the recrystallization heating temperature is preferably 800°C or higher.

[0096] <Ratio of α-phase and β-phase> The ratios of the α-phase and β-phase contained in each orthogonal cross-section V of the first to sixth foils are shown in the graph of Fig. 15. The ratios of the α-phase and β-phase contained in the orthogonal cross-section V were derived by an EBSD analyzer (Symmetry S2 manufactured by Oxford Instruments) based on the respective scan areas (28.3 μm × 21.2 μm) of the parallel cross-section P and the orthogonal cross-section V.

[0097] Looking at the graph of Fig. 15, in any of the first to sixth foils, the α-phase is 3% or less and the β-phase is 97% or more. That is, it was confirmed that according to the method for manufacturing the foil or the method for treating the foil of this example, the α-phase contained in the foil can be made 10% or less and the β-phase can be made 90% or more.

[0098] Also, looking at the graph of Fig. 15, it can be seen that in any of the foils with a final rolling reduction rate of 75% and 90%, as the recrystallization heating temperature increases, the ratio of the α-phase decreases and the ratio of the β-phase tends to increase.

[0099] <Comparison of average grain size by area-weighted average> The average grain sizes in the respective orthogonal cross-sections V of the first to sixth foils are shown in the graph of Fig. 16. The average grain size shown in the graph of Fig. 16 is for the grains contained in the region of the orthogonal cross-section V shown in Figs. 10 and 11, and was derived by area-weighted average. The area-weighted average is the average value of the values obtained by multiplying the ratio of the area of each crystal grain to the total area by the area value of each crystal grain. The average grain size by area-weighted average was derived by an EBSD analyzer (Symmetry S2 manufactured by Oxford Instruments).

[0100] Looking at the graph of Fig. 16, the average particle size by area-weighted average of the crystal grains is the largest at 12.22 μm for the second foil and the smallest at 8.84 μm for the fourth foil. Thus, it was confirmed that the average particle size by area-weighted average of the crystal grains contained in the foil of this titanium alloy is in the range of 8.8 μm or more and 12.3 μm or less. As a result, according to the method for manufacturing the foil or the method for treating the foil of this example, it was confirmed that the average particle size by area-weighted average of the crystal grains contained in the foil of this titanium alloy can be controlled in the range of 8.8 μm or more and 12.3 μm or less. Note that the average particle size by area-weighted average of the crystal grains contained in the foil of this titanium alloy can be further widened, and it can be speculated that it is also possible to set it in the range of 8.7 μm or more and 16.5 μm or less. And the above range of the average particle size can be adjusted, for example, by adjusting the rolling reduction rate in the rolling process and / or the heating temperature in the recrystallization heating process.

[0101] Also, looking at the graph of Fig. 16, it can be seen that the foil with a final rolling reduction rate of 75% has a larger average particle size than the foil with a final rolling reduction rate of 90%. Thus, it can be speculated that the lower the final rolling reduction rate, the larger the average particle size by area-weighted average compared to the higher final rolling reduction rate.

[0102] Also, in both the foil with a final rolling reduction rate of 75% and the foil with a final rolling reduction rate of 90%, it can be seen that the average particle size by area-weighted average is larger when the recrystallization heating temperature is 800 °C or higher compared to when the recrystallization heating temperature is 780 °C. Thus, it was confirmed that increasing the crystal heating temperature results in a larger average particle size by area-weighted average. This point can also be confirmed by visually observing the size of the crystal grains shown in Figs. 10 and 11, as explained in <Comparison of Crystal Grains>.

[0103] From the above results, it was confirmed that by adjusting the final rolling reduction rate and the recrystallization heating temperature in the recrystallization heating process, the number of crystal grains arranged in the thickness direction of the foil or the average particle size by area-weighted average can be controlled.

[0104] <Cooling Rate> As a result of verifying the orthogonal cross-sections of the first comparative example foil to the sixth comparative example foil, it was confirmed that at the first cooling rate (-100 °C decrease per 10 minutes, the cooling rate by furnace cooling) until the temperature of the foil reached 600 °C, it was insufficient to suppress the growth of crystal grains in the structure of the foil due to recrystallization. Further, as a result of verifying the orthogonal cross-sections of the first foil to the sixth foil of the present example, it was confirmed that at the second cooling rate (-300 °C decrease per 10 minutes) until the temperature of the foil reached 600 °C, it was possible to suppress the growth of crystal grains in the structure of the foil due to recrystallization. From the above verification results, it can be inferred that even at the third cooling rate (-150 °C decrease per 10 minutes) until the temperature of the foil reaches 600 °C, the growth of crystal grains in the structure of the foil due to recrystallization can be suppressed, and the size of crystal grains per one in the thickness direction of the foil (length in the thickness direction of the foil) can be suppressed. That is, it is considered that if the foil is cooled at a cooling rate equal to or higher than the third cooling rate in the foil treatment cooling step, the number of crystal grains in the thickness direction of the foil can be controlled.

[0105] Note that the method for manufacturing a foil, the method for treating a foil, and the foil of the present invention are not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention. And, of course, all the methods for manufacturing a foil, the methods for treating a foil, and the foils configured by extracting each of the constituent elements in the present embodiment and appropriately combining them are also included in the scope of the present invention.

Explanation of Reference Numerals

[0106] 10 Titanium alloy plate 11 Titanium alloy rolled material 20 Cold rolling device 21, 21 Rolling rollers 30 Furnace 31 Accommodation part 32 Base material 33 Weight material 34 Heating part 35 Vacuum generation part 40 Blower

Claims

1. A recrystallization heating step of heating a foil made of a titanium alloy containing tantalum under vacuum or in an atmosphere of an inert gas to recrystallize the structure of the foil; After the recrystallization heating step, the foil is cooled at a cooling rate of at least -150°C per minute in the range until the temperature of the foil reaches 600°C under vacuum or in an atmosphere of an inert gas, to suppress the growth of crystal grains of the structure of the foil accompanying the recrystallization; a foil treatment cooling step; characterized by comprising: A method for treating a foil.

2. A recrystallization heating step of heating a foil made of a titanium alloy containing tantalum under vacuum or in an atmosphere of an inert gas to recrystallize the structure of the foil; After the recrystallization heating step, the foil is cooled by forced cooling to lower the temperature of the foil faster than natural cooling under vacuum or in an atmosphere of an inert gas, to suppress the growth of crystal grains of the structure of the foil accompanying the recrystallization; a foil treatment cooling step; characterized by comprising: A method for treating a foil.

3. When the total of the titanium alloy is 100 atomic%, the titanium alloy contains 15 atomic% to 27 atomic% of tantalum, 1 atomic% to 8 atomic% of tin, and 0.4 atomic% to 1.7 atomic% of oxygen, and the balance is composed of titanium and unavoidable impurities, The method for treating a foil according to claim 1 or 2.

4. The degree of vacuum under the above-mentioned vacuum is 1×10 －２ (Pa) or less, characterized in that The method for treating a foil according to claim 1 or 2.

5. The heating temperature of the foil in the recrystallization heating step is in the range of 700 to 900°C, The method for treating a foil according to claim 1 or 2.

6. The recrystallization heating step A housing part capable of housing the foil; A vacuum generating part for evacuating the inside of the housing part; A heating part for heating the housing part; is carried out in a furnace having, The foil treatment cooling step is characterized in that the housing part housing the foil is cooled from the outside under an atmosphere of an inert gas or under vacuum to cool the foil. The method for treating a foil according to claim 1 or 2.

7. The ratio of the α-phase contained in the foil after the foil treatment cooling step is 10% or less, and the ratio of the β-phase is 90% or more, The method for treating a foil according to claim 1 or 2.

8. By adjusting the heating temperature in the recrystallization heating step, the average particle diameter by area-weighted average of crystal grains contained in the foil or the number of crystal grains arranged in the thickness direction of the foil is controlled, The method for manufacturing a foil according to claim 1 or 2.

9. A foil forming step of processing a titanium alloy material made of a titanium alloy containing tantalum to form a foil, A foil treatment step of performing a treatment on the foil, comprising: The foil forming step includes: A rolling step of rolling the titanium alloy material into a foil, An annealing step of heating the titanium alloy material that has undergone the rolling step at an annealing temperature and annealing it, A foil forming cooling step of cooling the titanium alloy material that has undergone the annealing step, having: The foil treatment step includes: A recrystallization heating step of heating the foil under vacuum or in an atmosphere of an inert gas to recrystallize the structure of the foil, After the recrystallization heating step, in a range until the temperature of the foil reaches 600 °C under vacuum or in an atmosphere of an inert gas, cooling the foil at a cooling rate of at least -150 °C per minute to suppress the growth of crystal grains of the structure of the foil accompanying the recrystallization, a foil treatment cooling step, characterized by having: A method for manufacturing a foil.

10. A foil forming step of processing a titanium alloy material made of a titanium alloy containing tantalum to form a foil, A foil treatment step of performing a treatment on the foil, comprising: The foil forming step includes: A rolling step of rolling the titanium alloy material into a foil, An annealing step of heating the titanium alloy material that has undergone the rolling step at an annealing temperature and annealing it, A foil forming cooling step of cooling the titanium alloy material that has undergone the annealing step, having: The foil treatment step includes: A recrystallization heating step of heating the foil under vacuum or in an atmosphere of an inert gas to recrystallize the structure of the foil, After the recrystallization heating step, in a vacuum or in an atmosphere of an inert gas, cooling the foil by forced cooling to lower the temperature of the foil faster than in the case of natural cooling, to suppress the growth of crystal grains of the structure of the foil accompanying the recrystallization, a foil treatment cooling step, characterized by having: A method for manufacturing a foil.

11. When the total of the titanium alloy is 100 atomic%, the titanium alloy contains 15 atomic% to 27 atomic% of tantalum, 1 atomic% to 8 atomic% of tin, and 0.4 atomic% to 1.7 atomic% of oxygen, and the balance is composed of titanium and unavoidable impurities, The method for manufacturing a foil according to claim 9 or 10.

12. The foil forming step has a processing step of performing a processing treatment on the titanium alloy material at least once before the rolling step, The processing step includes: A second rolling step of rolling the titanium alloy material to reduce the thickness of the titanium alloy material, A second annealing step of heating and annealing the titanium alloy material that has undergone the second rolling step at an annealing temperature; A second foil-forming cooling step of cooling the titanium alloy material that has undergone the second annealing step; characterized by comprising: The method for manufacturing a foil according to claim 9 or 10.

13. By adjusting the rolling reduction rate in the rolling step, controlling the average particle diameter by area-weighted average of crystal grains contained in the foil or the number of crystal grains arranged in the thickness direction of the foil. Characterized by this. The method for manufacturing a foil according to claim 9 or 10.

14. A foil made of a titanium alloy, When the entire titanium alloy is 100 atomic%, it contains 15 atomic% to 27 atomic% of tantalum, 1 atomic% to 8 atomic% of tin, and 0.4 atomic% to 1.7 atomic% of oxygen, and the balance is composed of titanium and unavoidable impurities. The average particle diameter by area-weighted average of crystal grains contained in itself is in the range of 8.7 μm or more and 16.5 μm or less. The ratio of the α-phase contained in itself is 10% or less, and the ratio of the β-phase is 90% or more. Characterized by this. Foil.

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