Titanium alloy material and method for producing the same

Abstract

To provide a titanium alloy material that is better in strength and toughness than conventional titanium alloy, offering a good balance between both properties of strength and toughness.SOLUTION: A titanium alloy material contains, in mass%, Al: 4.6% or more and 8.0% or less, Fe: 0.01% or more and 2.0% or less, Cu: 0.3% or more and 2.5% or less, O: 0.03% or more and 0.25% or less with the balance being Ti and impurities.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a titanium alloy material and a method for manufacturing the same.

Background Art

[0002] In recent years, as described in Non-Patent Document 1, a new manufacturing method called three-dimensional lamination manufacturing technology has been developed and applied to metal materials. The three-dimensional lamination manufacturing technology is generally known as 3D printer technology. Recently, it is collectively referred to as Additive Manufacturing (AM) technology together with various technologies for manufacturing practical members such as industrial products by sequentially adding materials to obtain a three-dimensional shape, and has attracted attention around the world.

[0003] In the terminology definition by the International Organization for Standardization (ISO 52900), AM technology is defined as a process of bonding materials to manufacture a member from 3D model data, and is classified into the following categories: Binder Jetting (BJT), Directed Energy Deposition (DED), Materials Extrusion (MEX), Material Jetting (MJT), Powder Bed Fusion (PBF), Sheet Lamination (SHL), Vat Photo Polymerization (VPP). Among these, the three types applied to metal materials are BJT (binder jetting method), DED (directed energy deposition method), and PBF (powder bed fusion bonding method).

[0004] These methods for metals are attracting attention because they require less man-hours for manufacturing compared to conventional metal processing methods, are expected to improve the yield, and can shorten the manufacturing period and reduce the manufacturing cost.

[0005] When manufacturing metal components by AM technology (additive manufacturing technology), in any of the above methods such as PBF (powder bed fusion method), since the metal is finally melted and solidified for shaping, the resulting metal components have a solidified structure. Such metal components are further used as actual components after reducing internal defects, improving material properties, and enhancing shape accuracy through HIP treatment, forging, heat treatment, machining, etc., as required.

[0006] By the way, titanium alloy, a type of metal material, is lightweight and high-strength, and has good biocompatibility with the living body, so it is used in the aerospace field and medical fields such as implants. Among titanium alloys, the Ti-6Al-4V alloy, an α+β type titanium alloy with high strength and excellent balance with ductility, is widely used.

[0007] In many cases, α+β type titanium alloys such as Ti-6Al-4V are used by melting and solidifying raw materials mixed with sponge titanium or master alloy to produce ingots, and then subjecting the ingots to elongation processes such as forging and rolling to obtain elongated materials such as plates, bars, wires, and profiles, and then processing them into a predetermined member shape to obtain titanium alloy materials. In this case, in the manufacturing process of titanium alloy materials, various processing and heat treatments are carried out so that an equiaxed crystal structure can be obtained for applications where strength and ductility are required, and a needle-like crystal structure can be obtained for applications where fracture toughness and creep resistance are required.

[0008] However, as described above, the use of additive manufacturing technology as a means of manufacturing components made of metal materials, and manufacturing components with a solidified structure by melting and solidifying to form a predetermined shape, is increasing. Also, conventionally, in some applications, casting materials with a solidified structure obtained by melting and solidifying raw materials mixed with sponge titanium or master alloy, or raw materials with a predetermined chemical composition, have been used. Titanium alloy materials manufactured through melting and solidification, like these, do not undergo rolling or heat treatment, so they have a solidified structure that is inferior in strength and toughness.

[0009] Regarding the metallographic morphology of titanium alloys manufactured by additive manufacturing technology, Patent Document 1 describes a titanium alloy that can form an object having an equiaxed crystal structure (without a subsequent processing step for eliminating the columnar crystal structure) using an additive manufacturing process. According to this, additively manufactured titanium alloys produce coarse columnar crystals, resulting in undesirable anisotropic mechanical properties. However, by incorporating an effective amount of a β eutectoid stabilizer, an equiaxed crystal structure can be produced when the titanium alloy is melted or sintered during the additive manufacturing process. Here, it is described that the β eutectoid stabilizer can be selected from Fe, Ni, Cu, or combinations thereof.

[0010] By the way, in terms of the chemical composition of titanium alloys, instead of Ti-6Al-4V alloys, Ti-Al-Fe-based titanium alloys containing inexpensive Al and Fe are known (Patent Document 2). Also, Ti-Fe-Cu-based titanium alloys in which inexpensive Cu is added to improve the high-temperature strength compared to industrial pure titanium are known (Patent Document 3).

[0011] In addition, Patent Document 4 describes a titanium alloy with controlled addition amounts of Al, O, Cu, Sn, and Si as a titanium alloy that is stronger than existing alloys that can be coil-rolled, has high cold rolling properties, and also has workability. Furthermore, Patent Document 5 describes a titanium alloy with controlled addition amounts of Al, Cr, Fe, Cu, Ni, and C as a titanium alloy that exhibits strength, hot workability, and excellent machinability.

[0012] Also, Patent Document 6 describes a method for producing a titanium alloy with a tensile strength of 1000 - 1500 MPa and an elongation of 9 - 15% by mixing Cu powder with titanium alloy powder and incorporating Cu in a high concentration range of 1 - 10% by the elemental powder mixing method.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Non-Patent Document

[0014]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0015] However, when additive manufacturing technology is applied as a method for manufacturing a titanium alloy material and a titanium alloy material having a solidification structure is manufactured by melting and solidifying, it is difficult to control the metal structure in subsequent processing heat treatment to improve strength and toughness. Therefore, a titanium alloy having excellent strength and toughness is desired even in the state of the solidification structure.

[0016] In response to such problems, the technique described in Patent Document 1 is a technique for reducing the anisotropy of mechanical properties by reducing columnar crystals generated by melting or sintering to obtain an equiaxed crystal structure, but a method for improving strength and toughness is not described. In addition, the titanium alloy described in Patent Document 2 is an alloy aimed at replacing expensive V raw material of Ti-Al-V alloy with inexpensive Fe, and although there is a description regarding tensile properties, the impact value is not mentioned. Patent Document 3 relates to a heat-resistant titanium alloy plate containing inexpensive Cu, and describes the tensile properties at room temperature and high temperature, but does not mention the impact value. Patent Document 4 relates to a titanium alloy with good cold rolling properties, and does not mention anything about the solidification structure excellent in strength and toughness. Patent Document 5 relates to a titanium alloy with good cold rolling properties and a titanium alloy with excellent machinability, and is not a titanium alloy produced through melting and solidification. Patent Document 6 is a method for manufacturing a titanium alloy containing a high concentration of Cu by the elemental powder mixing method, but does not mention the mechanical properties of a titanium alloy having a solidification structure formed by melting and solidification.

[0017] Moreover, not only for additive manufacturing technology, but also for titanium alloy materials having a solidification structure produced by a general casting process, it is required to be excellent in strength and toughness, and also to have an excellent balance between strength and toughness. Furthermore, for titanium alloy materials having a processed structure different from the solidification structure, which are produced through a casting process, a hot working process, a heat treatment process, etc., it is required to be excellent in strength and toughness, and also to have an excellent balance between strength and toughness.

[0018] The present invention has been made in view of the above circumstances, and an object thereof is to obtain a titanium alloy material that is superior in strength and toughness to conventional titanium alloys, and further superior in the balance between both properties of strength and toughness.

Means for Solving the Problems

[0019] The present invention for solving the above problems comprises the following configuration 。 1 In mass%, containing Al: 4.6% or more and 8.0% or less, Fe: 0.01% or more and 2.0% or less, Cu: 0.3% or more and 2.5% or less, O: 0.03% or more and 0.25% or less, and the balance: Ti and impurities, A titanium alloy material satisfying the following formula (1). ​0.4×TS + CIS ≥ 370 … (1) In formula (1), CIS is the impact value (unit: J / cm 2 ) obtained by dividing the impact absorption energy determined by the Charpy test at 25°C by the cross-sectional area of the test piece, and TS is the tensile strength (unit: MPa). 2 Further, instead of a part of Ti, it contains one or more of Sn: 5.0% or less, Nb: 8.0% or less, Si: 1.0% or less, and Mo: 5.0% or less by mass%, [1] The titanium alloy material described in 3 A part or all of the metal structure is a solidification structure composed of columnar crystal grains and equiaxed crystal grains, the titanium alloy material described in [1] or in [2] 4 Using a titanium alloy powder containing, by mass%, Al: 4.6% or more and 8.0% or less, Fe: 0.01% or more and 2.0% or less, Cu: 0.3% or more and 2.5% or less, O: 0.03% or more and 0.25% or less, with the balance being Ti and impurities, as a raw material, and by additive manufacturing technology, 3 The manufacturing method of a titanium alloy material for manufacturing the titanium alloy material described in 5 The additive manufacturing technology is a directed energy deposition method or a powder bed fusion bonding method, 4 The manufacturing method of the titanium alloy material described in 6 Laying a titanium alloy powder containing, by mass%, Al: 4.6% or more and 8.0% or less, Fe: 0.01% or more and 2.0% or less, Cu: 0.3% or more and 2.5% or less, O: 0.03% or more and 0.25% or less, with the balance being Ti and impurities, in layers to form a powder bed, and irradiating the surface of the powder bed with a high-energy beam to dissolve and solidify a part of the powder bed, a first step; Laying the titanium alloy powder in layers on the powder bed to form a new powder bed, and irradiating the surface of the new powder bed with a high-energy beam to dissolve and solidify a part of the new powder bed, a second step, and After performing the first step, repeating the second step at least once or more,​​​​​​3 A method for manufacturing a titanium alloy material according to the titanium alloy material described in 7 In mass %, containing Al: 4.6% or more and 8.0% or less, Fe: 0.01% or more and 2.0% or less, Cu: 0.3% or more and 2.5% or less, O: 0.03% or more and 0.25% or less, with the balance being Ti and impurities, while supplying a titanium alloy material composed of powder or wire onto a substrate, irradiating the titanium alloy material with a high-energy beam, melting and solidifying the titanium alloy material on the substrate, and depositing a solidified metal on the substrate, 3 A method for manufacturing a titanium alloy material according to the titanium alloy material described in 8 The titanium alloy powder further contains, in mass %, one or more of Sn: 5.0% or less, Nb: 8.0% or less, Si: 1.0% or less, Mo: 5.0% or less, in place of a part of Ti, 4 to 7 The method for manufacturing a titanium alloy material according to any one of 9 4 to 8 A method for manufacturing a titanium alloy material, in which one or more of hot working, cold working, straightening, and cutting are performed on the titanium alloy material obtained by the method for manufacturing a titanium alloy material according to any one of

Advantages of the Invention

[0020] According to the present invention, a titanium alloy material having superior strength and toughness compared to conventional titanium alloys, and further having an excellent balance between the two characteristics of strength and toughness can be obtained. The present invention is not limited to a titanium alloy material having a solidified structure, and may be a titanium alloy member having a worked structure. In the case of having a worked structure, a titanium alloy material capable of achieving a higher-level balance between the two characteristics of strength and toughness can be obtained. ​​​In addition, the titanium alloy material of the present invention can be used for members of various applications manufactured by additive manufacturing. Furthermore, as a titanium alloy material having an excellent balance of both strength and toughness characteristics, the titanium alloy material of the present invention can contribute to energy saving and resource saving by taking advantage of its lightweight and high-strength characteristics.

Embodiments for Carrying Out the Invention

[0021] The present inventor has studied a chemical composition that is superior in strength and toughness to existing titanium alloys, and further superior in the balance between strength and toughness, in various metal microstructures such as solidification microstructures and processed microstructures, particularly in the state of solidification microstructures, and has found a component system that provides good characteristics. In this specification, the term "solidification microstructure" is used to mean a metal microstructure obtained through the processes of melting and solidification. Also, the term "processed microstructure" is used to mean a metal microstructure other than a solidification microstructure such as a cast material, specifically, a processed microstructure obtained by further performing hot working, annealing, etc., or a metal microstructure such as an annealed microstructure.

[0022] Furthermore, for example, the solidification microstructure can be exemplified by a structure composed of columnar crystal grains and equiaxed crystal grains. Also, the processed microstructure can be exemplified by a structure composed of elongated crystal grains and equiaxed crystal grains. These are classified based on the difference in the shape in the crystal with respect to the classification in the manufacturing process. Elongated crystal grains are formed by deforming, contracting, or a combination thereof, the equiaxed crystal grains formed by recrystallization during annealing in a specific direction. Also, it includes a needle-like structure (β phase) formed by heat treatment as described later, specifically, heat treatment involving transformation, and precipitates of various shapes (including equiaxed grains). When observing a cross-section of any part of the titanium alloy, the aspect ratio of the equiaxed crystal grains is approximately 1, whereas the aspect ratio of the elongated crystal grains is a value other than 1. When the equiaxed crystal grains after annealing are spherical, the equiaxed crystal grains are circular, and the elongated crystal grains after processing are elliptical. The processed microstructure is not limited to those described above.

[0023] As an index of the toughness of the titanium alloy, the impact value (CIS) obtained by dividing the impact energy absorbed in the Charpy test at 25°C by the cross-sectional area of the test piece was used. As a result of investigations by the inventors, it was found that for conventional titanium alloys such as Ti-6Al-4V, the relationship between the impact value (CIS, unit: J / cm 2 ) and the tensile strength (TS, unit: MPa) is in the range of 0.4×TS + CIS < 370. That is, it was found that the sum of 0.4 times the value of the impact value (J / cm 2 ) and the value of the strength (MPa) is at most less than 370. Therefore, in conventional titanium alloys, even if the balance between strength and toughness was achieved, the strength and toughness themselves were not high. Thus, various investigations were conducted to simultaneously achieve 0.4×TS + CIS ≥ 370 for the relationship between toughness and strength, CIS ≥ 30 for toughness, and TS ≥ 620 which is equal to or higher than the existing Ti-3Al-2.5V alloy for strength. As a result, by appropriately controlling the addition amounts of Al, Fe, Cu, and O, a titanium alloy excellent in both impact value and strength was found even in the state of the solidification structure. Hereinafter, a titanium alloy material and a method for manufacturing the same according to an embodiment of the present invention will be described.

[0024] The titanium alloy material of the present embodiment contains, by mass%, Al: 4.6% or more and 8.0% or less, Fe: 0.01% or more and 2.0% or less, Cu: 0.3% or more and 2.5% or less, O: 0.03% or more and 0.25% or less, and the balance consists of Ti and impurities. Further, the titanium alloy material of the present embodiment is an α + β type titanium alloy material.

[0025] Hereinafter, the chemical composition of the titanium alloy material of the present embodiment will be described. In the following description, the “%” indication of the content of each element of the chemical composition means “mass%”. Further, the numerical range represented by using “~” means a range including the numerical values described before and after “~” as the lower limit value and the upper limit value. In addition, when “exceeding” or “less than” is attached to the numerical values described before and after “~”, the numerical range means a range not including these numerical values as the lower limit value or the upper limit value.

[0026] Al is an α-phase stabilizing element and mainly an element that strengthens the α-phase. When the Al content is less than 4.6%, it becomes difficult to ensure a tensile strength of 620 MPa or more corresponding to Ti-3Al-2.5V (ASTM grade 9) of the α + β type titanium alloy. On the other hand, when the Al content exceeds 8.0%, the ductility decreases significantly and the toughness decreases. Also, as will be described later, in order to enjoy the effect of the combined addition of Al and Cu, an Al content of less than 4.6% is insufficient, and the effect of the combined addition can be obtained by setting the Al content to 4.6% or more. Therefore, the Al content is set to 4.6% or more and 8.0% or less. The Al content may be 5.0% or more, may be 5.5% or more, may be 7.0% or less, or may be 6.5% or less.

[0027] Fe is a β-phase stabilizing element. Compared with other elements, the amount of solid solution in the α-phase is small. When the amount of solid solution in the α-phase is exceeded, the titanium alloy is made into two phases, α-phase and β-phase, to improve the strength. In the titanium alloy material of the present invention, since Cu, which is also a β-stabilizing element, is added simultaneously, if Fe is 0.01% or more, the effect can be obtained. On the other hand, when Fe exceeds 2.0%, the influence of grain boundary segregation becomes large and the toughness begins to decrease. Furthermore, when a compound with Ti precipitates exceeding the solid solubility limit of Fe, the toughness decreases significantly. Therefore, the Fe content is set to 0.01% or more and 2.0% or less. The Fe content may be 0.2% or more or may be 1.7% or less.

[0028] Cu is a β-stabilizing element. Similar to Fe, it is made into two phases, α-phase and β-phase, to improve the strength. At the same time, Cu can be solid-solved in the α-phase up to about 2.5% at most, improving the strength of the titanium alloy material. Furthermore, even when solid-solved in the α-phase, it does not suppress the twin deformation, which is a kind of deformation mechanism of the α-phase, so it hardly impairs the ductility and toughness of the α-phase. Therefore, it is an essential additive element for improving the balance between strength and toughness. When Cu exceeds 2.5%, the amount of solid solution in the α-phase becomes saturated, and the compound of Ti and Cu precipitates coarsely, resulting in a decrease in toughness. On the other hand, when Cu is less than 0.3%, the effect of improving the balance between strength and ductility becomes poor.

[0029] In addition, the maximum solid solubility of Cu in the α phase increases as the Al content increases, is hardly affected by the Fe content, and decreases as the O content increases. Therefore, in the titanium alloy material according to the present invention containing 4.6% or more of Al, the effect of Cu can be more greatly enjoyed. When Al exceeds 8.0%, although the strength increases, the toughness decreases as described above.

[0030] Therefore, the Cu content is set to 0.3% or more and 2.5% or less. The Cu content may be 0.5% or more and may be 2.0% or less.

[0031] O is an α-phase stabilizing element and an element that strengthens the α phase. However, when the O content increases, the toughness decreases, so it is preferably 0.25% or less. On the other hand, O is an element that is difficult to remove in titanium smelting, and excessive cost increase is incurred to make it less than 0.03%. Therefore, the lower limit is preferably 0.03% or more.

[0032] Furthermore, in the present invention, in addition to the above elements, instead of a part of Ti, one or more of Sn: 5.0% or less, Nb: 8.0% or less, Si: 1.0% or less, and Mo: 5.0% or less can be contained.

[0033] Sn is an element that dissolves in both the α phase and the β phase and strengthens both phases. When it dissolves in the α phase, like Cu, it can be strengthened without impairing ductility and toughness, but its effect is smaller compared to Cu. When the Sn content exceeds 5.0%, the toughness decreases. Therefore, the Sn content is set to 5.0% or less. When Sn is contained, it may be 0.2% or more, may be 0.5% or more, or may be 1.0% or more.

[0034] Nb is a β-stabilizing element, and a part of it solid-solves in the α-phase to strengthen it. However, its strengthening ability per mass% is small compared to Fe, Cu, and Sn. When the Nb content exceeds 8.0%, its effect saturates. Therefore, the Nb content should be 8.0% or less. When adding Nb, it may be 0.2% or more, 0.5% or more, or 1.0% or more.

[0035] Si is a β-stabilizing element, and it also solid-solves in the α-phase, having a large effect of improving the strength of the alloy. However, when Si exceeds 1.0%, the compound of Ti and Si precipitates coarsely, resulting in a decrease in toughness. Therefore, the Si content should be 1.0% or less. When adding Si, it may be 0.2% or more, or 0.3% or more.

[0036] Mo is a β-stabilizing element, and its strengthening ability per mass% is greater than that of Cu. However, when it exceeds 5.0%, the α-phase precipitating in the β-phase becomes too fine, resulting in a significant decrease in toughness. Therefore, the Mo content should be 5.0% or less. When adding Mo, it may be 0.2% or more, 0.5% or more, or 1.0% or more.

[0037] The balance in the chemical composition may be Ti and impurities. Specifically, examples of impurities include Cl, Na, Mg, Ca mixed in the refining process, and Zr, Ta, V mixed from scrap. When these impurities are contained, their contents are, for example, each 0.1% or less, and the total amount is 0.3% or less, which is a level without problems.

[0038] In addition, Cr or Ni, which are typical eutectoid β-stabilizing elements, stabilize the β phase like Fe and contribute to the strength improvement by two-phase transformation, so they may be used as a partial or total substitute for Fe. However, when one or both of Cr and Ni are contained in the Ti-Al-Fe-Cu-O system, which is the basic component system of the present invention, the solid solution amount of Cu in the α phase decreases, and the effect of improving the strength and ductility balance by Cu cannot be obtained. Therefore, it is preferable to keep Cr or Ni at a level contained as impurities from sponge titanium, titanium scrap, etc., which are titanium raw materials. The level is preferably such that the respective concentrations of Cr and Ni are 0.1% or less.

[0039] Next, the solidification structure of the titanium alloy material of the present embodiment will be described. The titanium alloy material according to the present embodiment generally has a chemical composition called an α + β type titanium alloy, and its metal structure contains 70% or more of the α phase and 30% or less of the β phase at room temperature. Also, depending on the contained elements and manufacturing history, compounds of Ti and Cu, Ti and Fe, and Ti and Si may be present in a total amount of 3% or less.

[0040] When the titanium alloy having the chemical composition according to the present embodiment is solidified from the molten state, columnar crystals are continuously formed in the solidification direction. As the metal phase, first, the β phase (bcc structure) is formed, and as the temperature decreases, the α phase (hcp structure) is formed at the grain boundaries and within the grains of the β phase.

[0041] The crystal grain size of the β phase formed during solidification varies depending on the size of the titanium alloy material to be manufactured, the cooling method, etc. In the case of a member with a size of about several tens of mm or less on one side, the crystal grain size of the β phase when observed in a cross-section perpendicular to the solidification direction is 2 mm or less. Also, in the case of a member with a length of about several hundreds of mm on one side, the crystal grain size of the β phase when observed in a cross-section perpendicular to the solidification direction is about 50 mm.

[0042] In the solidified structure, the α-phase formed at the grain boundaries of the β-phase is generally called grain boundary α, and its thickness is 5 μm or less. When the cooling rate is high, grain boundary α is not formed. The α-phase formed within the grains is generally called acicular α, and has a form with a thickness of 5 μm or less and an aspect ratio of 3 or more. Except when the cooling rate is high, acicular α often forms a colony structure in which grains having substantially the same crystal orientation are formed in layers. The size of the colony structure generally has a positive correlation with the crystal grain size of the β-phase.

[0043] Note that the β-phase remains at room temperature, and in some cases, a part of it forms a β” phase or an ω-phase, or compounds of Ti and Cu, compounds of Ti and Fe, and compounds of Ti and Si may be formed. The larger the crystal grain size of the β-phase, or the larger the colony size of the α-phase formed within the β-phase, the strength and toughness may decrease. In addition, the ω-phase and the compound of Ti and Fe may significantly reduce the toughness. To reduce the crystal grain size of the β-phase and the colony size of the α-phase, it is advantageous to increase the cooling rate when solidifying the molten metal.

[0044] As described above, the titanium alloy material of the present embodiment may have a solidified structure composed of columnar and equiaxed (in shape) crystal grains.

[0045] In addition, the metal structure of the titanium alloy material of the present embodiment is not limited to having the above-described solidified structure, and may have a worked structure. Examples of the worked structure include, for example, elongated crystal grains obtained by applying processing involving deformation such as hot rolling to a member having a solidified structure such as a casting material, equiaxed crystal grains obtained by further annealing, acicular crystal grains obtained by heat treatment involving transformation as described above, and a structure containing precipitates of various shapes (including equiaxed grains).

[0046] The titanium alloy material of the present embodiment has excellent toughness and strength regardless of whether the metal structure is a solidified structure, a worked structure, or any other structure. That is, the titanium alloy material of the present embodiment has an impact value (CIS, unit: J / cm obtained by dividing the impact energy absorbed in the Charpy test at 25 °C by the cross-sectional area of the test piece.2 ) and the relationship with the tensile strength (TS, unit: MPa) is 0.4×TS + CIS ≥ 370, with respect to toughness, CIS ≥ 30, and with respect to strength, TS ≥ 620 is achieved. Such toughness and strength can be achieved even if the titanium alloy material of the present embodiment has a solidification structure. Also, even if the titanium alloy material of the present embodiment has a solidification structure that is generally considered to have inferior toughness compared to a processed structure, the above-mentioned toughness and strength can be achieved.

[0047] Next, a method for manufacturing the titanium alloy material according to the present embodiment will be described. The method for manufacturing the titanium alloy material according to the present embodiment is not particularly limited and can be manufactured by a general casting and solidification method, and can also be manufactured by an additive manufacturing technique. Furthermore, it can also be manufactured by a method of obtaining a plate material, a bar material, a pipe material, etc. by performing hot rolling or the like on an ingot.

[0048] When manufacturing the titanium alloy material of the present embodiment by a general casting and solidification method, metal raw materials such as sponge titanium, aluminum, iron, and copper are mixed, and after compression molding as necessary, it can be manufactured as an ingot by a consumable electrode vacuum arc melting method (VAR), an electron beam melting method (EBR), a plasma arc melting method (PAM), etc. As the raw materials, not only pure metals but also master alloys and scraps may be used. The form of the raw materials can be a lump, a plate, a powder, etc. The melted raw materials are generally cooled and solidified using a water-cooled copper mold.

[0049] Also, when manufacturing the titanium alloy material of the present embodiment by an additive manufacturing technique, for example, it can be manufactured using a directed energy deposition method or a powder bed fusion method.

[0050] In the case of the powder bed fusion method, metal raw materials such as sponge titanium, aluminum, iron, and copper are mixed, and after compression molding if necessary, they are melted by methods such as the consumable electrode vacuum arc melting method (VAR), electron beam melting method (EBR), plasma arc melting method (PAM), etc. Then, titanium alloy powder is produced by means such as the gas atomization method.

[0051] Next, the obtained titanium alloy powder is spread in layers to form a powder bed, and a first step is performed in which a part of the powder bed is melted and solidified by irradiating the surface of the powder bed with a high-energy beam.

[0052] Next, titanium alloy powder is spread in layers on the powder bed to form a new powder bed, and a second step is performed in which a part of the new powder bed is melted and solidified by irradiating the surface of the new powder bed with a high-energy beam.

[0053] After performing the first step, by repeating the second step at least once or more, a titanium alloy material having a predetermined shape can be manufactured.

[0054] Also, in the case of the directed energy deposition method, metal raw materials such as sponge titanium, aluminum, iron, and copper are mixed, and after compression molding if necessary, they are melted by methods such as the consumable electrode vacuum arc melting method (VAR), electron beam melting method (EBR), plasma arc melting method (PAM), etc. Then, titanium alloy powder is produced by means such as the gas atomization method. Alternatively, after melting, it is solidified into a slab, and this slab is hot-rolled to obtain a titanium alloy wire. These titanium alloy powder or titanium alloy wire are used as titanium alloy materials.

[0055] Next, while supplying the powdery or wire-shaped titanium alloy material onto a base material, the titanium alloy material is irradiated with a high-energy beam, and the titanium alloy material is melted and solidified on the base material to deposit a solidified metal on the base material, thereby manufacturing a titanium alloy material having a predetermined shape.

[0056] The titanium alloy materials produced by using the above-mentioned directional energy deposition method or powder bed fusion method will all have a solidification structure.

[0057] For titanium alloy materials produced by general casting solidification methods or additive manufacturing techniques, general processing and heat treatments such as HIP treatment, forging, extrusion, rolling, cutting, etc. may be further performed for the purpose of reducing internal defects and shape control.

[0058] Therefore, the titanium alloy material according to the present embodiment may have a structure containing, in addition to the solidification structure including the columnar crystal and equiaxed crystal grains, for example, their extended granular crystals, equiaxed grains, extended grains, or the above-mentioned compounds having a rectangular shape. Further, by subjecting the titanium alloy material having the above solidification structure to general processing and heat treatments of titanium alloys such as forging, rolling, extrusion, bending, cutting, heat treatment, etc., it may be used as an extended material such as a plate, bar, or tube.

[0059] Furthermore, when manufacturing the titanium alloy material of the present embodiment by performing hot rolling or the like on a cast slab, for example, a casting material produced by the above general casting solidification method is used as a raw material, and hot rolling is performed on this raw material. Further, annealing, cold rolling, final annealing, etc. may be performed after hot rolling. In this way, a titanium alloy material having a processed structure can be obtained.

Example

[0060] Next, the present invention will be described in more detail with reference to examples. However, the examples described below are examples of the embodiments of the present invention and do not limit the present invention.

[0061] Titanium alloy materials were produced by a general melting and solidification method. That is, metal raw materials with their formulations adjusted to have the chemical compositions shown in Table 1 were vacuum arc melted to obtain molten metals, and these molten metals were poured into water-cooled copper molds to produce disc-shaped titanium alloy materials (No. 1 to 34) with a diameter of 60 mm, a thickness of 10 mm, and a weight of about 100 g. The blanks in Table 1 indicate that alloy elements were not actively contained.

[0062] Since the titanium alloy materials numbered 1 to 34 were cooled from below by a water-cooled copper mold, a solidification structure composed of columnar crystal grains and equiaxed crystal grains extending from the lower surface to the upper surface of the disk was formed. From this titanium alloy material, a tensile test piece with a parallel part diameter of 3 mm and a parallel part length of 20 mm was taken such that the longitudinal direction of the test piece was parallel to the lower surface. Also, a 2 mm V-notch subsize Charpy test piece with a thickness of 5 mm and a width of 10 mm was taken such that the longitudinal direction of the test piece was parallel to the lower surface and the notch was in the thickness direction.

[0063] The tensile test was carried out at room temperature with a crosshead displacement rate of 0.3 mm / min. The impact test was carried out at room temperature (25 °C) using a 300 J Charpy impact testing machine. The impact test results were evaluated by the impact value (J / cm 2 ) obtained by dividing the absorbed energy by the cross-sectional area of the test piece.

[0064] Table 2 shows the results of the tensile strength and the impact value corresponding to each chemical composition in Table 1. The tensile strength was based on the tensile strength of the existing alloy Ti-3Al-2.5V (JIS 61 types), which is 620 MPa, and a value of 620 MPa or more was considered qualified. Also, an impact value of 30 J / cm 2 or more was considered qualified. Furthermore, as an index for the balance of both characteristics of the tensile strength and the impact value, it was determined whether the following formula (1) was satisfied, and the case where the following formula (1) was satisfied was considered qualified. In the judgment column of Table 2, the case where the left side of formula (1) was 370 or more was indicated as 〇 (achieved), and the case where the left side of formula (1) was less than 370 was indicated as × (not achieved).

[0065] 0.4×TS + CIS ≥ 370 … (1)

[0066] Also, in the remarks columns of Table 1 and Table 2, the example corresponding to Claim 1 was denoted as Example 1, and the example corresponding to Claim 2 was denoted as Example 2.

[0067] No. 1 and 2 are titanium alloy materials with a conventional chemical composition of the Ti-Al-V system, which do not satisfy the formula (1) showing the relationship between the strength (TS) and the impact value (CIS), and are not preferable characteristics. Also, No. 2 has a low tensile strength and does not reach the qualified range.

[0068] No. 3 is a Ti-Al-Fe alloy without Cu, which did not satisfy the formula (1) showing the relationship between strength and impact value and was unqualified.

[0069] No. 4 has an Al content below the scope of the present invention, does not satisfy the formula (1) showing the relationship between strength and impact value, and was unqualified.

[0070] No. 5 - 15 have a chemical composition containing Al: 4.6 - 8.0%, Fe: 0.01 - 2.0%, Cu: 0.3 - 2.5%, O: 0.03 - 0.25%, with the balance being Ti and impurities, which satisfied the scope of the present invention, satisfied all of the strength, impact value, and the formula (1) showing the relationship between strength and impact value, and were qualified.

[0071] No. 16 has an Al content exceeding the scope of the present invention, and the impact value was unqualified.

[0072] No. 17 has an Fe content exceeding the scope of the present invention, and the impact value was unqualified.

[0073] No. 18 has a Cu content exceeding the scope of the present invention, does not satisfy the formula (1) showing the relationship between strength and impact value, and was unqualified.

[0074] No. 19 has an O content below the scope of the present invention, does not satisfy the strength and the formula (1) showing the relationship between strength and impact value, and was unqualified.

[0075] No. 20 has an O content exceeding the scope of the present invention, and the impact value was unqualified.

[0076] No. 21 - 23 are examples of adding Sn to the Ti-Al-Fe-Cu alloy. No. 21 and No. 22 satisfy the chemical composition of the present invention, satisfy the strength, impact value, and the formula (1) showing the relationship between strength and impact value, and were qualified. On the other hand, No. 23 has an Sn content exceeding the scope of the present invention, and the impact value was unqualified.

[0077] Examples Nos. 24 to 26 are those in which Si is further contained in the Ti-Al-Fe-Cu-based alloy. Nos. 24 and 25 satisfied the chemical composition of the present invention, satisfied all of the strength, impact value, and formula (1) showing the relationship between the strength and the impact value, and passed. On the other hand, in No. 26, the Si content exceeded the range of the present invention, and the impact value failed.

[0078] Examples Nos. 27 to 29 are those in which Si, Nb, and Mo are respectively combined and contained in the Ti-Al-Fe-Cu-Sn-based alloy. All of these satisfied the chemical composition of the present invention, satisfied all of the strength, impact value, and formula (1) showing the relationship between the strength and the impact value, and passed.

[0079] Examples Nos. 30 and 31 are those in which Nb is further contained in the Ti-Al-Fe-Cu-based alloy. No. 30 satisfied the chemical composition of the present invention, satisfied the strength, impact value, and formula (1) showing the relationship between the strength and the impact value, and passed. On the other hand, in No. 31, the Nb content exceeded the range of the present invention, and the impact value failed.

[0080] Examples Nos. 32 to 34 are those in which Mo is further contained in the Ti-Al-Fe-Cu-based alloy. Nos. 32 and 33 satisfied the chemical composition of the present invention, satisfied the strength, impact value, and formula (1) showing the relationship between the strength and the impact value, and passed. On the other hand, in No. 34, the Mo content exceeded the range of the present invention, and the impact value failed.

[0081] Also, the metal structures of Nos. 1 to 34 were solidified structures composed of columnar crystal grains and equiaxed crystal grains.

[0082] Next, a titanium alloy material was manufactured by the wire and arc-based additive manufacturing (WAAM) method using a titanium alloy wire as a raw material. Specifically, as the titanium alloy raw material, a titanium alloy wire (φ1.6 mm) with the chemical composition shown in Table 3 was prepared. For the additive manufacturing, a plasma welding torch was used, and the current value was set to 200 A. Also, the substrate was a titanium alloy plate with a thickness of 12.7 mm. The pre-set additive manufacturing area on the substrate was surrounded by a chamber and shielded with Ar gas at a flow rate of 15 L / min. While supplying the titanium alloy wire at a speed of 200 mm / min, the wire was melted by the plasma welding torch and then solidified on the substrate. By performing the additive process of repeating such operations multiple times, a titanium alloy material composed of an additive manufactured sample with a width of 18 mm, a length of 100 mm, and a thickness of 15 mm was produced.

[0083] In the same manner as described above, a tensile test piece and a Charpy test piece with a 2 mm V-notch sub-size were taken from the obtained titanium alloy material, and a tensile test and a Charpy impact test were conducted at room temperature (25 °C). Table 4 shows the results of the tensile strength and impact values corresponding to each chemical composition in Table 3.

[0084] Nos. 35 to 37 are examples of Ti-Al-Fe-Cu-O-based alloys. Also, No. 38 is an example in which Si is further contained in the Ti-Al-Fe-Cu-O-based alloy. All of them satisfied the chemical composition of the present invention, satisfied the strength, impact value, and formula (1) showing the relationship between the strength and the impact value, and passed.

[0085] Also, the metallographic structures of Nos. 35 to 37 were solidification structures composed of columnar crystal grains and equiaxed crystal grains.

[0086] Next, after manufacturing a titanium alloy material by a general melting and solidification method, forging and hot rolling were performed to obtain a plate shape. That is, a metal raw material whose composition was adjusted to have each chemical composition shown in Table 5 was melted by vacuum arc melting to obtain a molten metal, and this molten metal was poured into a water-cooled copper mold to produce a cylindrical titanium alloy material (No. 41 to 44) with a diameter of 430 mm, a length of 300 mm, and a weight of about 200 kg. The blanks in Table 5 indicate that alloy elements were not actively contained.

[0087] Each titanium alloy material was hot forged at a heating temperature of 1100°C to a thickness of 220 mm and a width of 100 mm, and then the scale was removed. Subsequently, hot rolling was performed at a heating temperature of 1050°C to produce a plate with a thickness of 5 mm.

[0088] Tensile test specimens were fabricated with the thickness remaining the same as the plate thickness, a width of 6 mm in the parallel part, and a length of 30 mm in a direction perpendicular to the rolling direction. The tensile test was conducted at a crosshead displacement rate of 0.75 mm / min. Also, impact test specimens were fabricated with the thickness remaining the same as the plate thickness, a length of 55 mm in the rolling direction of the plate, a width of 10 mm in the plate width direction, and a 2 mm V-notch in the plate thickness direction. Both the tensile test and the impact test were conducted at room temperature (25°C). Table 6 shows the results of the tensile strength and impact values corresponding to each chemical composition in Table 5.

[0089] No. 41 is a Ti - Al - Fe - O - based Ti alloy that does not contain Cu, and its impact value is less than 30 J / cm 2 and it does not satisfy the formula (1) showing the relationship between strength and impact value, so it was unqualified.

[0090] No. 42 and 43 are Ti alloys containing Cu, which satisfy the component range of the present invention, satisfy the impact value and the formula (1) showing the relationship between strength and impact value, and were qualified.

[0091] No. 44 is an example containing further Si, which satisfies the component range of the present invention, satisfies the impact value and the formula (1) showing the relationship between strength and impact value, and was qualified.

[0092] In addition, the metal structures of Nos. 41 to 44 were wrought structures composed of elongated grains and equiaxed grains.

[0093]

Table 1

[0094]

Table 2

[0095]

Table 3

[0096]

Table 4

[0097]

Table 5

[0098]

Table 6

Claims

1. By mass%, it contains Al: 4.6% or more and 8.0% or less, Fe: 0.01% or more and 2.0% or less, Cu: 0.3% or more and 2.5% or less, O: 0.03% or more and 0.25% or less, and the balance: Ti and impurities, A titanium alloy material satisfying the following formula (1). 0.4 × TS + CIS ≥ 370... (1) In formula (1), CIS is the impact value obtained by dividing the impact absorption energy determined by the Charpy test at 25°C by the cross-sectional area of the test piece (unit: J / cm ２ ), and TS is the tensile strength (unit: MPa).

2. Furthermore, in place of a part of Ti, by mass%, it contains one or more of Sn: 5.0% or less, Nb: 8.0% or less, Si: 1.0% or less, Mo: 5.0% or less, the titanium alloy material according to Claim 1.

3. The titanium alloy material according to Claim 1 or Claim 2, wherein part or all of the metal structure is a solidification structure composed of columnar crystal grains and equiaxed crystal grains.

4. Using a titanium alloy powder containing, by mass%, Al: 4.6% or more and 8.0% or less, Fe: 0.01% or more and 2.0% or less, Cu: 0.3% or more and 2.5% or less, O: 0.03% or more and 0.25% or less, and the balance being Ti and impurities as a raw material, a method for manufacturing a titanium alloy material, which manufactures the titanium alloy material according to Claim 3 by an additive manufacturing technique.

5. The method for manufacturing a titanium alloy material according to Claim 4, wherein the additive manufacturing technique is a directed energy deposition method or a powder bed fusion method.

6. Laying a titanium alloy powder containing, by mass%, Al: 4.6% or more and 8.0% or less, Fe: 0.01% or more and 2.0% or less, Cu: 0.3% or more and 2.5% or less, O: 0.03% or more and 0.25% or less, and the balance being Ti and impurities in layers to form a powder bed, and irradiating the surface of the powder bed with a high-energy beam to dissolve and solidify a part of the powder bed in a first step; Laying the titanium alloy powder in layers on the powder bed to form a new powder bed, and irradiating the surface of the new powder bed with a high-energy beam to dissolve and solidify a part of the new powder bed in a second step, A method for manufacturing a titanium alloy material, which manufactures the titanium alloy material according to Claim 3 by repeating the second step at least once or more after performing the first step.

7. A titanium alloy material in mass %, containing Al: 4.6% or more and 8.0% or less, Fe: 0.01% or more and 2.0% or less, Cu: 0.3% or more and 2.5% or less, O: 0.03% or more and 0.25% or less, with the balance being Ti and impurities, and being in the form of powder or wire, while supplying the titanium alloy material onto a substrate, irradiating the titanium alloy material with a high energy beam, melting and solidifying the titanium alloy material on the substrate to deposit a solidified metal on the substrate, thereby manufacturing the titanium alloy material according to claim 3, a method for manufacturing a titanium alloy material.

8. The method for manufacturing a titanium alloy material according to any one of claims 4 to 7, wherein the titanium alloy powder further contains, in mass %, one or more of Sn: 5.0% or less, Nb: 8.0% or less, Si: 1.0% or less, Mo: 5.0% or less, in place of a part of Ti.

9. A method for manufacturing a titanium alloy material, wherein one or more of hot working, cold working, straightening, and cutting are performed on the titanium alloy material obtained by the method for manufacturing a titanium alloy material according to any one of claims 4 to 8.

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