JP7741445B2 - Titanium alloy material, titanium alloy wire, titanium alloy powder, and method for producing titanium alloy material - Google Patents

Description

The present invention relates to titanium alloy materials, titanium alloy wires, titanium alloy powders, and methods for producing titanium alloy materials.

In recent years, as described in Non-Patent Document 1, a new manufacturing method known as 3D additive manufacturing (AM) has been developed and is now being applied to metal materials. 3D additive manufacturing (AM) is generally known as 3D printer technology, but it has recently come to be collectively referred to as additive manufacturing (AM), along with various other techniques for manufacturing practical components such as industrial products by sequentially adding material to obtain three-dimensional shapes, and is attracting attention worldwide.

The International Organization for Standardization's definition (ISO 52900) defines AM technology as a process for combining materials to manufacture components from 3D model data, and classifies it into the following categories: Binder Jetting (BJT), Directed Energy Deposition (DED), Materials Extrusion (MEX), Material Jetting (MJT), Powder Bed Fusion (PBF), Sheet Lamination (SHL), and Vacuum Photo Polymerization (VPP). Of these, three methods are applied to metal materials: BJT (binder jetting), DED (directed energy deposition), and PBF (powder bed fusion).

These metal techniques are attracting attention because they require fewer manufacturing steps than conventional metal processing methods, are expected to improve yields, shorten manufacturing times, and reduce manufacturing costs.

When manufacturing metal components using AM (additive manufacturing) technology, whether using the above-mentioned methods or powder bed fusion (PBF), the metal is ultimately melted and solidified to form the desired shape, resulting in a solidified structure. Such metal components can then be further processed as needed by HIP, forging, heat treatment, cutting, etc. to reduce internal defects, improve material properties, and increase shape precision before being used as actual parts.

Titanium alloys, a type of metallic material, are lightweight, strong, and have good biocompatibility, making them popular in the aircraft and medical fields, such as for implants. Among titanium alloys, Ti-6Al-4V alloy, an α+β titanium alloy with an excellent balance of high strength and ductility, is widely used.

In many cases, alpha-beta titanium alloys such as Ti-6Al-4V are made by melting and solidifying a raw material mixture of sponge titanium and master alloy to produce an ingot. The ingot is then subjected to wrought processes such as forging and rolling to produce wrought materials such as plates, bars, and shapes, which are then processed into the desired shape to produce the titanium alloy material. In this case, the titanium alloy material undergoes various processing and heat treatments during the manufacturing process to obtain an equiaxed crystal structure for applications requiring strength and ductility, and an acicular crystal structure for applications requiring fracture toughness and creep resistance.

However, as mentioned above, additive manufacturing technology is being adopted as a means of producing components made from metallic materials, and there are increasing examples of components being produced that are shaped into a predetermined shape through melting and solidification, and have a solidified structure. Furthermore, some applications have traditionally used cast materials with a solidified structure obtained by melting and solidifying raw materials containing a mixture of titanium sponge or master alloys, or raw materials with a predetermined chemical composition. Titanium alloy materials produced through melting and solidification in this way have not undergone rolling or heat treatment, and therefore have a solidified structure that is inferior in strength and toughness.

Regarding the metallographic morphology of titanium alloys produced by additive manufacturing techniques, Patent Document 1 describes a titanium alloy that can be formed using an additive manufacturing process to have an equiaxed crystal structure (without a subsequent processing step to eliminate the columnar crystal structure). According to this document, additively manufactured titanium alloys produce coarse columnar crystals, resulting in undesirable anisotropic mechanical properties. However, by incorporating an effective amount of a β-eutectic stabilizer, an equiaxed crystal structure can be produced when the titanium alloy is melted or sintered during the additive manufacturing process. It is stated that the β-eutectic stabilizer can be selected from Fe, Ni, Cu, or a combination thereof.

In terms of the chemical composition of titanium alloys, Ti-Al-Fe-based titanium alloys containing inexpensive Al and Fe are known as an alternative to Ti-6Al-4V alloys (Patent Document 2). Also known is a Ti-Fe-Cu-based titanium alloy that adds inexpensive Cu to improve high-temperature strength over commercially pure titanium (Patent Document 3).

Patent Document 4 describes a titanium alloy with controlled amounts of Al, O, Cu, Sn, and Si added, which has higher strength than existing alloys that can be rolled into coils, excellent cold rolling properties, and workability. Furthermore, Patent Document 5 describes a titanium alloy with controlled amounts of Al, Cr, Fe, Cu, Ni, and C added, which exhibits strength, hot workability, and excellent machinability.

Patent document 6 also 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 using an elemental powder mixing method to increase the Cu content to a high concentration of 1-10%.

Japan Special Table Publication No. 2020-511597 Japanese Patent Publication No. 4-358036 Japanese Patent Application Publication No. 2005-298970 Japanese Patent Application Publication No. 2014-001421 Japanese Patent Application Publication No. 2016-183407 Japanese Patent Application Publication No. 2013-112860

Fundamentals of 3D additive manufacturing technology for metallic materials, Yuichiro Koizumi, Masahiko Chiba, Naoyuki Nomura, Takayuki Nakano, Materia, Vol. 56, No. 12 (2017), pp. 686-690

However, when additive manufacturing technology is used to produce titanium alloy materials with a solidified structure by melting and solidifying them, it is difficult to control the metal structure in subsequent thermomechanical processing to improve strength and toughness. Therefore, there is a demand for titanium alloys that have excellent strength and toughness even in their solidified structure state.

To address these issues, the technology described in Patent Document 1 is a technology that reduces the anisotropy of mechanical properties by reducing the columnar crystals generated by melting or sintering to obtain an equiaxed crystal structure, but does not describe a method for improving strength or toughness.
Furthermore, the titanium alloy described in Patent Document 2 is an alloy intended to replace the expensive V raw material of the Ti-Al-V alloy with inexpensive Fe, and although there is a description regarding tensile properties, there is no mention of impact values.
Patent Document 3 relates to a heat-resistant titanium alloy plate containing inexpensive Cu, and describes the tensile properties at room temperature and at high temperatures, but does not mention the impact value.
Patent Document 4 relates to a titanium alloy having good cold rolling properties, but makes no mention of a solidification structure having excellent strength and toughness.
Patent Document 5 relates to a titanium alloy with good cold rolling properties and a titanium alloy with excellent machinability, but is not a titanium alloy produced through melting and solidification.
Patent Document 6 describes a method for producing a titanium alloy containing a high concentration of Cu by an elemental powder mixing method, but does not mention the mechanical properties of the titanium alloy having a solidified structure formed by melting and solidification.

Therefore, titanium alloy materials having a solidified structure are required to have excellent strength and toughness, and also to have an excellent balance between strength and toughness.
Furthermore, titanium alloy materials having a processed structure different from the solidified structure, which are manufactured through a casting process, a hot working process, a heat treatment process, etc., are also required to have excellent strength and toughness, as well as an excellent balance between strength and toughness.

The present invention was made in consideration of the above-mentioned circumstances, and aims to provide titanium alloy materials, titanium alloy wires, titanium alloy powders, and methods for manufacturing titanium alloy materials that are superior in strength and toughness to conventional titanium alloys and also have an excellent balance of both strength and toughness properties.

The gist of the present invention, which solves the above problems, is as follows.
[1] A titanium alloy material according to one embodiment of the present invention contains, by mass%, Al: 4.6% or more and 8.0% or less, Fe: 0.2% or more and 1.5% or less, Cu: 0.3% or more and 2.0% or less, O: 0.03% or more and 0.20% or less, Sn: 0% or more and 3.0% or less, Nb: 0% or more and 8.0% or less, Si: 0% or more and 0.80% or less, and Mo: 0% or more and 2.0% or less, with the balance being Ti and impurities. At least a portion of the titanium alloy material contains an α phase and a β phase as a metallographic structure, the average of the elliptical approximate major axis lengths of the α phases is 20 μm or more and 80 μm or less, the average of the aspect ratios of the α phases is 3.0 or more and 5.0 or less, and the impact value CIS, which is the value obtained by dividing the impact absorption energy obtained in a Charpy test at 25°C by the cross-sectional area of the test piece, is 40 J/cm ² or more, the tensile strength TS is 900 MPa or more, and the impact value CIS and the tensile strength TS satisfy 0.3×TS+CIS≧340.
[2] The titanium alloy material described in the above [1] may contain, by mass%, one or more selected from the group consisting of Sn: 0.2% or more and 3.0% or less, Nb: 0.2% or more and 8.0% or less, Si: 0.20% or more and 0.80% or less, and Mo: 0.2% or more and 2.0% or less.

[3] Another aspect of the present invention relates to a titanium alloy wire rod for producing the titanium alloy material described in [1] above, which contains, by mass%, Al: 4.6% or more and 8.0% or less, Fe: 0.2% or more and 1.5% or less, Cu: 0.3% or more and 2.0% or less, O: 0.03% or more and 0.20% or less, Sn: 0% or more and 3.0% or less, Nb: 0% or more and 8.0% or less, Si: 0% or more and 0.80% or less, and Mo: 0% or more and 2.0% or less, with the balance being Ti and impurities, and has a maximum diameter of 1.0 mm or more and 8.0 mm or less, and a tensile strength of 900 MPa or more.

[4] A titanium alloy powder according to yet another aspect of the present invention is a titanium alloy powder for producing the titanium alloy material described in [1] above, containing, by mass%, Al: 4.6% or more and 8.0% or less, Fe: 0.2% or more and 1.5% or less, Cu: 0.3% or more and 2.0% or less, O: 0.03% or more and 0.20% or less, Sn: 0% or more and 3.0% or less, Nb: 0% or more and 8.0% or less, Si: 0% or more and 0.80% or less, and Mo: 0% or more and 2.0% or less, the balance being Ti and impurities, and having an average particle size of 10 μm or more and 100 μm or less, and a standard deviation of the particle size of 5 μm or more and 15 μm or less.

[5] A further aspect of the present invention relates to a method of manufacturing a titanium alloy material for manufacturing the titanium alloy material described in [1] above, which contains, by mass%, Al: 4.6% or more and 8.0% or less, Fe: 0.2% or more and 1.5% or less, Cu: 0.3% or more and 2.0% or less, O: 0.03% or more and 0.20% or less, Sn: 0% or more and 3.0% or less, Nb: 0% or more and 8.0% or less, Si: 0% or more and 0.80% or less, and Mo: 0% or more and 2.0% or less, with the balance being Ti and impurities. The method comprises a first step of spreading pure titanium alloy powder in a layer to form a powder bed, and irradiating the surface of the powder bed with a high-energy beam to melt and solidify a portion of the powder bed, and a second step of spreading the titanium alloy powder in a layer on top of the powder bed to form a new powder bed, and irradiating the surface of the new powder bed with a high-energy beam to melt and solidify a portion of the new powder bed, and after performing the first step, the second step is repeated at least once.

[6] A method for producing a titanium alloy material according to yet another embodiment of the present invention is a method for producing the titanium alloy material described in [1] above, comprising the steps of: supplying a titanium alloy material comprising, by mass%, Al: 4.6% or more and 8.0% or less, Fe: 0.2% or more and 1.5% or less, Cu: 0.3% or more and 2.0% or less, O: 0.03% or more and 0.20% or less, Sn: 0% or more and 3.0% or less, Nb: 0% or more and 8.0% or less, Si: 0% or more and 0.80% or less, and Mo: 0% or more and 2.0% or less, with the balance being Ti and impurities, in the form of a powder or wire rod, onto a substrate; irradiating the titanium alloy material with a high-energy beam to melt and solidify the titanium alloy material on the substrate, thereby depositing a solidified metal on the substrate.
[7] In the method for producing a titanium alloy material according to the above [5] or [6], the titanium alloy material obtained by the method for producing a titanium alloy material according to the above [5] or [6] may be subjected to one or more of hot working, cold working, straightening, and cutting.

According to the present disclosure, it is possible to obtain titanium alloy materials, titanium alloy wires, and titanium alloy powders that are superior in strength and toughness to conventional titanium alloys and that have an excellent balance between the strength and toughness properties.
The present disclosure is not limited to titanium alloy materials having a solidified structure, but may also be a titanium alloy material having a worked structure. In the case of a worked structure, a titanium alloy material can be obtained that can achieve a higher level of balance between the properties of strength and toughness.
Furthermore, the titanium alloy material of the present disclosure can be used for components for a wide variety of applications manufactured by additive manufacturing. Furthermore, as a titanium alloy material with an excellent balance of strength and toughness, the titanium alloy material of the present disclosure can contribute to energy and resource conservation by taking advantage of its lightweight and high-strength properties.

FIG. 1 is a diagram showing an example of an Image Quality map of a titanium alloy material according to an embodiment of the present invention, obtained by EBSD. FIG. 1 is a diagram showing an example of an Image Quality map of a conventional titanium alloy material by EBSD.

<Titanium alloy material>
Titanium alloy materials are not limited to titanium alloy materials having a solidification structure in part or in whole, but also include titanium alloy materials having a processed structure. The inventors have investigated chemical compositions that are superior in strength and toughness to existing titanium alloys and also have an excellent balance of strength and toughness in various metallographic states such as solidification structures and processed structures, particularly in solidification structure states, and have discovered a component system that provides favorable properties. In this specification, the term "solidification structure" is used to refer to a metallographic structure obtained through the processes of melting and solidification. Furthermore, the term "processed structure" is used to refer to a metallographic structure other than a solidification structure such as a cast material, specifically a metallographic structure obtained by further hot working, heat treatment, etc., such as a processed structure or a heat-treated structure.

Furthermore, examples of solidification structures include structures composed of columnar grains and equiaxed grains. Examples of processed structures include structures composed of elongated grains and equiaxed grains formed by recrystallization. These are classified based on the differences in the crystal shape, in contrast to classifications based on the manufacturing process. Columnar grains generally form in a columnar shape from the surface toward the center of a titanium alloy material. Equiaxed grains may form in the center. Elongated grains are formed by stretching or shrinking the solidification structure or equiaxed grains in a specific direction through deformation, or a combination of these. Equiaxed grains are formed by recrystallization through heat treatment of elongated grains after processing. Processed structures include acicular structures (mainly α and β phases), equiaxed structures (mainly α phases), and precipitates of various shapes (including equiaxed grains) formed by heat treatment, as described below, specifically heat treatment involving transformation. When observing an arbitrary cross section of a titanium alloy, the aspect ratio of equiaxed crystal grains is approximately 1, while the aspect ratio of elongated crystal grains is a value other than 1. If the equiaxed crystal grains after heat treatment are spherical, the equiaxed crystal grains will be circular, and the elongated crystal grains after processing will be elliptical. The processed structure is not limited to the above.

As an index of the toughness of titanium alloy materials, the impact value (CIS), calculated by dividing the impact absorption energy determined in a Charpy impact test at 25°C by the cross-sectional area of the test piece, was used. As a result of studies by the inventors, it was found that the relationship between impact value (CIS, unit: J/cm ² ) and tensile strength (TS, unit: MPa) of conventional titanium alloys such as Ti-6Al-4V is in the range of 0.3×TS+CIS<340. That is, it was found that the maximum sum of the value of 0.3 times the tensile strength (MPa) and the impact value (J/cm ² ) is less than 340. Therefore, even if a balance between strength and toughness is achieved in conventional titanium alloys, the strength and toughness themselves are not high. Therefore, various studies were conducted to simultaneously achieve a relationship between toughness and strength of 0.3×TS+CIS≧340, which means that CIS≧40 in terms of toughness, and a strength of TS≧900, which exceeds that of the existing Ti-3Al-2.5V alloy. As a result, by appropriately controlling the amounts of Al, Fe, Cu, and O added, a titanium alloy was discovered that exhibits excellent impact value and strength even in the solidified structure state.
Hereinafter, a titanium alloy material according to an embodiment of the present invention, a method for producing the same, and a titanium alloy wire and titanium alloy powder that can be used to produce the titanium alloy will be described.

The titanium alloy material of this embodiment has a chemical composition containing, by mass%, Al: 4.6% to 8.0%, Fe: 0.2% to 1.5%, Cu: 0.3% to 2.0%, O: 0.03% to 0.20%, Sn: 0% to 3.0%, Nb: 0% to 8.0%, Si: 0% to 0.8%, and Mo: 0% to 2.0%, with the balance being Ti and impurities. Furthermore, the titanium alloy material of this embodiment is an α+β titanium alloy material.

The chemical composition of the titanium alloy material of this embodiment will be described below. In the following description, the "%" used to indicate the content of each element in the chemical composition means "mass %." Furthermore, when a numerical range is expressed using "to", it means a range that includes the numerical values written before and after "to" as the lower and upper limits. Furthermore, when the numerical values written before and after "to" are followed by "greater than" or "less than", it means a range that does not include these numerical values as the lower or upper limit.

Al is an α-phase stabilizer and primarily strengthens the α-phase. If the Al content is less than 4.6%, it becomes difficult to achieve a tensile strength of 900 MPa or more, which is equivalent to or greater than that of the α+β titanium alloy Ti-3Al-2.5V (ASTM grade 9). On the other hand, if the Al content exceeds 8.0%, ductility decreases significantly, resulting in a decrease in toughness. Furthermore, as described below, an Al content of less than 4.6% is insufficient to achieve the combined effects of Al and Cu, but an Al content of 4.6% or more can achieve the combined effects. Therefore, the Al content is set to 4.6% or more and 8.0% or less. The Al content is preferably 4.8% or more, more preferably 5.0% or more. The Al content may be preferably 7.8% or less, more preferably 7.5% or less.

Fe is a β-phase stabilizing element, and its solid solubility in the α-phase is low compared to other elements. However, when its solid solubility in the α-phase is exceeded, the titanium alloy undergoes a two-phase transformation into α and β phases, improving strength. In the titanium alloy material disclosed herein, Cu, another β-stabilizing element, is also added, so an Fe content of 0.2% or more provides this effect. On the other hand, when Fe exceeds 1.5%, the effects of grain boundary segregation become significant, and toughness begins to decrease. Furthermore, when Fe exceeds its solid solubility limit and compounds with Ti precipitate, toughness decreases significantly. Therefore, the Fe content is set to 0.2% or more and 1.5% or less. The Fe content may be preferably 0.3% or more, more preferably 0.5% or more. The Fe content may also be preferably 1.3% or less, more preferably 1.0% or less.

Cu is a β-stabilizing element that, like Fe, improves strength by forming a two-phase structure consisting of α and β phases. At the same time, Cu can dissolve in the α phase up to a maximum of 2.5%, improving the strength of titanium alloy materials. Furthermore, even when dissolved in the α phase, it does not inhibit twinning, a type of deformation mechanism in the α phase, and therefore hardly impairs the ductility and toughness of the α phase. Therefore, Cu is an essential additive element for improving the balance between strength and toughness. However, if Cu exceeds 2.0%, coarse Ti and Cu compounds precipitate, reducing toughness. On the other hand, if Cu is less than 0.3%, the effect of improving the balance between strength and ductility is diminished.

In addition, the maximum amount of Cu dissolved in the α phase increases with increasing Al content, is hardly affected by the Fe content, and decreases with increasing O content. Therefore, the titanium alloy material according to the present disclosure, which contains 4.6% or more Al, can enjoy the effects of Cu to a greater extent. As mentioned above, when Al exceeds 8.0%, strength increases, but toughness decreases.

Therefore, the Cu content is set to 0.3% or more and 2.0% or less. The Cu content may be 0.5% or more. The Cu content may also be 1.5% or less.

O is an α-phase stabilizer and strengthens the α-phase. However, as a high O content reduces toughness, it is preferable that the O content be 0.20% or less. The O content is preferably 0.18% or less, more preferably 0.16% or less, and even more preferably 0.15% or less. On the other hand, O is an element that is difficult to remove during titanium smelting, and keeping it below 0.03% would result in excessive cost increases. Therefore, an O content of 0.03% or more is preferable. The O content is more preferably 0.04% or more, and even more preferably 0.05% or more.

Furthermore, in this disclosure, in addition to the above elements, one or more elements selected from the group consisting of Sn: 3.0% or less, Nb: 8.0% or less, Si: 0.80% or less, and Mo: 2.0% or less may be contained in place of a portion of Ti.

Sn is an element that dissolves in the α and β phases to strengthen both phases. When dissolved in the α phase, it can strengthen the material without impairing ductility and toughness, just like Cu, but the effect is smaller than that of Cu. Toughness decreases when the Sn content exceeds 3.0%. Therefore, when Sn is contained, the Sn content should be 3.0% or less. The Sn content is preferably 2.0% or less. Furthermore, when Sn is contained, the Sn content may be 0.2% or more, 0.5% or more, or 1.0% or more.

Nb is a β-stabilizing element, but some of it dissolves in the α-phase to strengthen it. However, its strengthening ability per mass percent is smaller than that of Fe, Cu, and Sn. When the Nb content exceeds 8.0%, the effect saturates. Therefore, if Nb is contained, the Nb content should be 8.0% or less. The Nb content is preferably 5.0% or less. Furthermore, if Nb is contained, the Nb content may be 0.2% or more, 0.5% or more, or 1.0% or more.

Si is a β-stabilizing element, but it also dissolves in the α-phase, significantly improving the strength of the alloy. However, if the Si content exceeds 0.80%, coarse Ti and Si compounds precipitate, reducing toughness. Therefore, if Si is included, the Si content should be 0.80% or less. The Si content is preferably 0.50% or less. Furthermore, if Si is included, the Si content may be 0.20% or more, or even 0.30% or more.

Mo is a β-stabilizing element and has a greater strengthening ability per mass percent than Cu. However, if it exceeds 2.0%, the α-phase precipitated in the β-phase becomes too fine, significantly reducing toughness. Therefore, if Mo is added, the Mo content should be 2.0% or less. The Mo content is preferably 1.8% or less. Furthermore, if Mo is added, the Mo content may be 0.2% or more, 0.5% or more, or 1.0% or more.

The remainder in the chemical composition may consist of Ti and impurities. Impurities include C, N, H, and other impurities. While these do not necessarily need to be present in titanium alloy materials, they are unavoidable impurities that are inevitably mixed in, making their inclusion in titanium alloy materials unavoidable. A C content of 0.20% or less, an N content of 0.20% or less, and an H content of 0.0150% or less are considered acceptable. Specific examples of other impurities include Cl, Na, Mg, and Ca, which are mixed in during the refining process, and Zr, Ta, V, Pt, Pd, Mn, Co, Y, B, Ru, W, Cr, and Ni, which are mixed in from scrap. The content of elements other than C, N, and H as impurities is, for example, 0.1% or less each, and a total of 0.5% or less is considered acceptable.

Furthermore, Cr or Ni, which are typical eutectoid β-stabilizing elements, are sometimes used as partial or complete substitutes for Fe because, like Fe, they stabilize the β phase and contribute to improving strength through the two-phase formation. However, adding either or both of Cr and Ni to the Ti-Al-Fe-Cu-O system, which is the basic component system of this disclosure, reduces the amount of Cu dissolved in the α phase, preventing the improvement in the balance between strength and ductility provided by Cu. Therefore, it is preferable to limit the amount of Cr or Ni to the level contained as an impurity in titanium raw materials such as sponge titanium and titanium scrap. Preferably, the concentration of each of Cr and Ni is 0.1% or less.

Next, the solidification structure of the titanium alloy material of this embodiment will be described. Figure 1 shows an example of an Image Quality map of a titanium alloy material according to one embodiment of the present invention, obtained by EBSD. Figure 2 shows an example of an Image Quality map of a conventional titanium alloy material, obtained by EBSD. As shown in Figure 2, a conventional titanium alloy material after hot working and heat treatment is composed of crystal grains of approximately several tens of μm, and is clearly different from the solidification structure of the titanium alloy material according to this embodiment, shown in Figure 1. The titanium alloy material according to this embodiment has a solidification structure in part below. The solidification structure of the titanium alloy material according to this embodiment will be described in detail. Note that the entire metal structure of the titanium alloy material according to this embodiment may be a solidification structure.

The titanium alloy material according to this embodiment has the chemical composition of a titanium alloy commonly known as an α+β 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. Depending on the elements contained and the manufacturing history, compounds of Ti and Cu, compounds of Ti and Fe, and compounds of Ti and Si may be present in a total amount of 3% or less.

When a titanium alloy having the chemical composition of this embodiment is solidified from a molten state, columnar crystals are formed continuously in the solidification direction, but the metal phase is first formed as a β phase (bcc structure), and as the temperature decreases, an α phase (hcp structure) is formed at the grain boundaries and within the grains of the β phase.

The grain size of the beta phase formed during solidification varies depending on the size of the titanium alloy material being manufactured, the holding time at high temperatures, the cooling method, etc., but for titanium alloy materials with sides measuring no more than a few tens of millimeters, the grain size of the beta phase when observed in a cross section perpendicular to the solidification direction is often no more than about 2 mm. Furthermore, for titanium alloy materials with sides measuring no more than a few hundred millimeters, the grain size of the beta phase when observed in a cross section perpendicular to the solidification direction is often no more than about 50 mm.

In addition, in solidification structures, the α phase formed at the grain boundaries of the β phase is generally called grain boundary α. When the cooling rate is fast, grain boundary α is not formed, and acicular α phase or α' phase is formed within the grains of the β phase. The acicular α phase formed within the β phase is generally called acicular α. Except when the cooling rate is fast, the acicular α often forms a colony structure in which grains with approximately 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.
In the α phase in the titanium alloy material according to this embodiment, the average length of the long axis of the ellipsoid is 20 μm or more and 80 μm or less. The average length of the long axis of the α phase is the average length of the long axis of the grain boundary α and the acicular α, which are ellipsoidally approximated. If the average length of the long axis of the α phase is 20 μm or more, the impact value is improved due to the effect of crack deflection. The average length of the long axis of the α phase is preferably 25 μm or more, more preferably 30 μm or more. Furthermore, if the average length of the long axis of the α phase is 80 μm or less, a high impact value can be obtained without excessively decreasing ductility. The average length of the long axis of the α phase is preferably 70 μm or less, more preferably 60 μm or less.

The average aspect ratio of the α phase is 3.0 or more and 5.0 or less. The average aspect ratio of the α phase here refers to the average aspect ratio of the grain boundary α and acicular α. If the average aspect ratio of the α phase is 3.0 or more, the impact value is improved due to the effect of crack deflection. The average aspect ratio of the α phase is preferably 3.2 or more, and more preferably 3.4 or more. If the average aspect ratio of the α phase is 5.0 or less, a high impact value can be obtained without excessively reducing ductility. The average aspect ratio of the α phase is preferably 4.8 or less, and more preferably 4.6 or less.

The average length of the long axis of the ellipsoid-approximated α phase and the average aspect ratio are measured using the following method. A rectangular parallelepiped test specimen measuring 3 to 20 mm in height and 3 to 20 mm in width, with a length of 1/4 to 3/4, is taken from the titanium alloy material. The height and width directions of the rectangular parallelepiped test specimen are aligned with the height and width directions of the titanium alloy material, respectively, and the center of the plane defined by the height and width directions of the rectangular parallelepiped test specimen is aligned with the half-height and half-width positions of the titanium alloy material. The plane defined by the height and width directions of the rectangular parallelepiped test specimen is used as the observation surface, and is roughly polished using emery paper. The width direction is perpendicular to the beam irradiation direction used in manufacturing the titanium alloy material. If it is difficult to determine the width direction, the shorter length within the plane perpendicular to the lamination direction is taken as the width direction. The height corresponds to the lamination direction. After rough polishing, the observation surface is buffed using colloidal silica to achieve a mirror finish. For the structural analysis, a scanning electron microscope (SEM) (JSM-7200F manufactured by JEOL Ltd.), electron backscatter diffraction (EBSD) (EBSD detector Velocity manufactured by TSL Solutions Co., Ltd.), and analysis software OIM analysis V7 are used. The measurement and analysis conditions are an acceleration voltage of 15 kV, a measurement magnification of 250x, a measurement field of view of 300 μm square or more, a measurement step of 0.5 μm, and a grain tolerance of 5°. The major axis length and aspect ratio obtained by elliptical approximation of the shape of the crystal grains determined to be α-phase from Kikuchi pattern analysis are obtained. There is no problem if the measurement field of view is 300 μm square or more. The area method, which takes into account the area, was used to calculate the average value. These analyses are performed using GUI operations on OIM Analysis. The ellipse approximation method is performed according to "Method 2 - Major = Maximum Distance, Minor = averaging scheme" described on page 442 of the OIM Analysis 7 manual.

In addition, the β phase remains even at room temperature, and some of it may form α" phase or ω phase, or compounds of Ti and Cu, Ti and Fe, or Ti and Si. The larger the crystal grain size of the β phase, or the larger the size of the α phase colonies formed within the β phase, the more likely it is that strength and toughness will decrease. Furthermore, the ω phase and compounds of Ti and Fe can significantly reduce toughness. In order 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.

The titanium alloy material of this embodiment may have a solidification structure consisting of columnar and equiaxed crystal grains, as described above.

Furthermore, the metal structure of the titanium alloy material of this embodiment is not limited to that having the solidification structure described above, but may also have a processed structure. Examples of processed structures include elongated grains obtained by subjecting a member having a solidification structure, such as a cast material, to processing involving deformation, such as hot rolling, equiaxed grains obtained by further heat treatment, acicular grains obtained by heat treatment involving transformation as described above, and structures containing precipitates of various shapes including equiaxed grains.

The titanium alloy material of this embodiment has excellent toughness and strength regardless of whether the metal structure is a solidified structure, a processed structure, or other structure. That is, the relationship between the impact value (CIS, unit: J/cm ² ) obtained by dividing the impact absorption energy obtained in a Charpy test at 25°C by the cross-sectional area of the test piece and the tensile strength (TS, unit: MPa) of the titanium alloy material of this embodiment is 0.3 × TS + CIS ≥ 340, and the toughness is CIS ≥ 40, while the strength is TS ≥ 900. Such toughness and strength can be achieved even if the titanium alloy material of this embodiment has a solidified structure. Furthermore, the above-mentioned toughness and strength can be achieved even if the titanium alloy material of this embodiment has a solidified structure, which is generally considered to have inferior toughness to a processed structure. CIS is preferably 45 or more. TS is preferably 950 MPa or more.

Next, a method for manufacturing a titanium alloy material according to this embodiment will be described.
The titanium alloy material according to this embodiment is manufactured by the additive manufacturing technology described above, and the manufacturing method of the titanium alloy material according to this embodiment is applied by powder bed fusion or directed energy deposition. The manufacturing methods of the titanium alloy material according to powder bed fusion and directed energy deposition will be described below.

(Powder Bed Fusion)
In the case of powder bed fusion, metallic raw materials such as sponge titanium, aluminum, iron, copper, etc. are mixed and, if necessary, compression molded, and then melted by a consumable electrode vacuum arc melting method (VAR), electron beam melting method (EBR), plasma arc melting method (PAM), etc., and, if necessary, forged or rolled into a rod, after which titanium alloy powder is produced by means of, for example, gas atomization.

Next, the obtained titanium alloy powder is spread in layers to form a powder bed, and the first step is carried out in which a high-energy beam is irradiated onto the surface of the powder bed to melt and solidify part of the powder bed. The thickness of the powder bed is, for example, 20 to 150 μm.

Next, a layer of titanium alloy powder is laid on top of the powder bed to form a new powder bed, and a second process is carried out in which a high-energy beam is irradiated onto the surface of this new powder bed to melt and solidify part of the new powder bed. The thickness of the powder bed in the second process is also the same as that of the powder bed in the first process, for example, 20 to 150 μm.

The heat input of the laser beam in each of the first and second steps is, for example, 5.0 to 30.0 J/ ^mm3 . The scanning speed of the laser beam is, for example, 400 to 900 mm/sec, and the laser output is 70 to 200 W. The laser beam diameter is, for example, 30 to 70 μm. The laser beam irradiation interval is, for example, 50 to 150 μm. The penetration depth is, for example, 10 to 150 μm. Furthermore, the laser beam irradiation atmosphere in the first and second steps is an inert gas atmosphere, for example, an argon atmosphere, to prevent oxidation.

After performing the first step, the second step can be repeated at least once to produce a titanium alloy material having a predetermined shape.

The powder used in the powder bed fusion method can be the titanium alloy powder described below, but it is not limited to this titanium alloy powder. It is also possible to use a mixed powder of titanium powder, aluminum powder, iron powder, copper powder, and other metal powders, as well as alloy powders containing portions of each, adjusted to have the chemical composition of a titanium alloy material.

(Directed Energy Deposition)
In the case of directed energy deposition, metal raw materials such as titanium sponge, aluminum, iron, and copper are mixed and compression molded as necessary, then melted by consumable electrode vacuum arc melting (VAR), electron beam melting (EBR), plasma arc melting (PAM), or the like, and forged or rolled as necessary to form a rod, which is then subjected to gas atomization or other methods to produce titanium alloy powder. Alternatively, the melted mixture is solidified to form a slab, which is then forged, rolled, and drawn to form a titanium alloy wire. These titanium alloy powders or titanium alloy wires are used as titanium alloy materials.

Next, while supplying the titanium alloy material in powder or wire form onto a substrate, a high-energy beam is irradiated onto the titanium alloy material, melting and solidifying the titanium alloy material on the substrate and depositing the solidified metal on the substrate, thereby producing a titanium alloy material having a predetermined shape. Examples of high-energy beams include electron beams, plasma arcs, and laser beams. Below, we will explain examples of when an electron beam is irradiated and when a plasma arc is used.

[Example using electron beam irradiation]
The titanium alloy material may be, for example, a wire rod having a diameter of 1.0 to 8.0 mm or a square bar having a cross-sectional area equal to that of the wire rod. The electron beam current may be, for example, 10 to 100 mA, and the feed rate of the titanium alloy material may be, for example, 1000 to 3000 mm/min. The thickness of the titanium alloy substrate may be, for example, 10 to 20 mm, and the titanium alloy substrate is cooled. The cooling rate when the temperature of the titanium alloy substrate is in the range of 1000 to 700°C may be, for example, 3.0°C/sec or more. The cooling rate when the temperature is less than 700°C may be, for example, 0.2°C/sec or more and 2.0°C/sec or less. The electron beam irradiation atmosphere is a vacuum atmosphere, for example, an atmosphere with a pressure of 1.3 × 10 ^-3 Pa or less.

[Plasma arc example]
The titanium alloy material may be, for example, a wire rod with a diameter of 1.0 to 8.0 mm or a square bar with a cross-sectional area equal to that of the wire rod. The plasma current may be, for example, 100 to 300 A, and the feed rate of the titanium alloy material may be, for example, 10 to 400 mm/min. The thickness of the titanium alloy substrate may be, for example, 10 to 20 mm, and the titanium alloy substrate is cooled. The cooling rate when the temperature of the titanium alloy substrate is in the range of 1000 to 700°C is, for example, 3.0°C/sec or more. The cooling rate when the temperature is less than 700°C is, for example, 0.2°C/sec or more and 3.0°C/sec or less. The plasma arc atmosphere is an inert gas atmosphere, such as an argon atmosphere, to prevent oxidation. The cooling rate of the titanium alloy substrate may be outside the above-mentioned range, as long as deformation due to thermal effects is suppressed and the cooling rate of the laminate is obtained.

When irradiating with a laser beam, the energy density, feed speed of the titanium alloy substrate, cooling rate, and irradiation atmosphere can be determined according to the properties required for the titanium alloy material to be manufactured.

In the directed energy deposition method, a powdered titanium alloy material may be used, and the feed rate of the powdered titanium alloy material is, for example, about 6 cm ³ /min in the case of electron beam irradiation and about 1 cm ³ /min in the case of plasma irradiation.

Titanium alloy materials produced using the above-mentioned directed energy deposition or powder bed fusion methods will both have a solidified structure.

Titanium alloy materials produced by additive manufacturing technology may be further subjected to common processes such as HIP treatment, forging, extrusion, and rolling in order to reduce internal defects and control the shape. The heating temperature during processes such as forging and rolling may be above the β transformation temperature or below the β transformation temperature. After the above processing, heat treatment is performed.

The heat treatment involves heating the titanium material to the higher of the β transformation temperature or 1000°C and holding the temperature for 60 minutes or less, and then cooling the surface of the titanium material at a cooling rate of 3.0°C/second or more while the temperature of the titanium material is in the range of 1000°C to 700°C. The holding time is preferably 30 minutes or less to prevent the crystal grains from becoming too coarse and reducing strength. The cooling rate is preferably 5.0°C/second or more.

The above processing before heat treatment may be omitted. Surface finishing such as cutting, milling, or polishing may also be performed. If surface finishing such as cutting, milling, or polishing is performed, it should be performed after processing and heat treatment.

Therefore, the titanium alloy material according to this embodiment may have a solidification structure containing the columnar and equiaxed crystal grains described above, as well as a structure containing the compounds described above, such as elongated crystals, equiaxed grains, elongated grains, or shapes including rectangular crystals. Furthermore, titanium alloy materials having the solidification structure described above may be further processed and heat-treated as in general titanium alloys, such as forging, rolling, extrusion, bending, cutting, and heat treatment, to produce wrought materials such as plates, rods, and tubes.

<Titanium alloy wire>
The titanium alloy wire used to manufacture the titanium alloy material has the same chemical composition as that of the titanium alloy material described above, a maximum diameter of 1.0 mm or more and 8.0 mm or less, and a tensile strength of 900 MPa or more.

The maximum diameter of the titanium alloy wire is 1.0 mm or more and 8.0 mm or less. To reduce the maximum diameter of titanium alloy wire to less than 1.0 mm, an additional wiredrawing process is required, which significantly increases manufacturing costs. Therefore, the maximum diameter of the titanium alloy wire is 1.0 mm or more. The maximum diameter of the titanium alloy wire is preferably 1.2 mm or more, and more preferably 1.4 mm or more. On the other hand, if the maximum diameter of the titanium alloy wire is 8.0 mm or less, the titanium alloy wire can be melted uniformly during the production of titanium alloy material. Therefore, the maximum diameter of the titanium alloy wire is 8.0 mm or less. If the maximum diameter of the titanium alloy wire is 4.8 mm or less, the titanium alloy wire can be melted more uniformly when irradiated with directed energy deposition energy. Therefore, the maximum diameter of the titanium alloy wire is preferably 3.2 mm or less. The maximum diameter of the titanium alloy wire is more preferably 2.0 mm or less.

The maximum diameter of titanium alloy wire is measured using the following method: the diameter of the wire is measured with a micrometer or vernier calipers at two or more locations per cross section, and at two or more cross sections per lot, and the maximum value is taken as the maximum diameter.

The tensile strength of the titanium alloy wire rod according to this embodiment is 900 MPa or more. This is because a tensile strength of 900 MPa or more for the titanium alloy wire rod according to this embodiment achieves a high tensile strength equal to or greater than that of titanium alloy Ti-3Al-2.5V manufactured by conventional methods. The tensile strength of the titanium alloy wire rod is preferably 920 MPa or more, and more preferably 930 MPa or more. On the other hand, there is no particular upper limit to the tensile strength of the titanium alloy wire rod, and the tensile strength of the titanium alloy wire rod can be, for example, 1300 MPa or less, or may be 1400 MPa or less.

The tensile strength of titanium alloy wire is measured using the following method. For titanium alloy wire with a maximum diameter of 6.0 mm or more and 8.0 mm or less, a round bar test specimen with a parallel section of φ3 mm, length of 20 mm, and gauge length of 10 mm is prepared from the titanium alloy wire and subjected to a tension speed of 10 mm/min at room temperature (25°C). For titanium alloy wire with a maximum diameter of less than 6.0 mm, a round bar test specimen with a gauge length of 100 mm is cut from the titanium alloy wire and subjected to a tension speed of 30 mm/min at room temperature (25°C).

For titanium alloy wire, the Vickers hardness is preferably 320 Hv or more and 380 Hv or less. If the Vickers hardness is 380 Hv or less, cracking during wire drawing is suppressed. If the Vickers hardness is 320 Hv or more, high strength can be achieved when titanium alloy material is manufactured using the wire.

The Vickers hardness of titanium alloy wire is measured in accordance with JIS Z 2244:2020 at the center of a cross section perpendicular to the long axis of each material, using a load of 1 kgf (9.8 N). The standard test specimen is 55 mm long and has a square cross section with sides of 10 mm. A V-notch is made at the center of the length, with a notch angle of 45 degrees, a notch depth of 2 mm, and a notch base radius of 0.25 mm. If a standard test specimen cannot be obtained, sub-size test specimens with thicknesses of 7.5 mm, 5 mm, or 2.5 mm may be used.

Next, we will explain one example of a method for manufacturing titanium alloy wire. Metal raw materials such as sponge titanium, aluminum, iron, and copper are mixed and compression molded as necessary, and then an ingot is produced using a method such as consumable electrode vacuum arc melting (VAR), electron beam melting (EBR), or plasma arc melting (PAM). The titanium alloy ingot is forged to produce a φ100 mm billet, which is heated to 950°C and then rolled. The rolled titanium alloy is repeatedly annealed at 700-800°C for 5-60 minutes and drawn using a cassette roller die or die drawing to achieve the desired diameter. The drawn titanium alloy is then annealed at a temperature of 700-750°C for 1 hour with air cooling.

<Titanium alloy powder>
The titanium alloy powder used to manufacture the titanium alloy material has the same chemical composition as the above-mentioned titanium alloy material, an average particle size of 10 μm or more and 100 μm or less, and a standard deviation of the particle size of 5 μm or more and 15 μm or less.

The average particle size of the titanium alloy powder is 10 μm or more and 100 μm or less. If the average particle size of the titanium alloy powder is less than 10 μm, the flowability will be poor. The average particle size of the titanium alloy powder is preferably 15 μm or more, and more preferably 20 μm or more. On the other hand, if the average particle size of the titanium alloy powder exceeds 100 μm, defects due to unmelted particles are more likely to occur. The average particle size of the titanium alloy powder is preferably 90 μm or less, and more preferably 80 μm or less.

The standard deviation of the particle size of the titanium alloy powder is 5 μm or more and 15 μm or less. If the standard deviation of the particle size of the titanium alloy powder is less than 5 μm, the yield will decrease significantly due to sieving. The standard deviation of the particle size of the titanium alloy powder is preferably 6 μm or more, and more preferably 7 μm or more. On the other hand, if the standard deviation of the particle size of the titanium alloy powder exceeds 15 μm, the flowability will decrease and defects will be more likely to occur. The standard deviation of the particle size of the titanium alloy powder is preferably 14 μm or less, and more preferably 13 μm or less.

The average particle size and standard deviation of particle size of titanium alloy powder are measured using a method in accordance with JIS Z 8825:2013 Particle size analysis - Laser diffraction and scattering method.

Next, we will explain one example of a method for producing titanium alloy powder. As mentioned above, titanium alloy powder is produced by mixing metal raw materials such as sponge titanium, aluminum, iron, and copper, and then compression molding the mixture as necessary.The mixture is then melted using a method such as consumable electrode vacuum arc melting (VAR), electron beam melting (EBR), or plasma arc melting (PAM), and then forged and rolled into rods, which are then further processed using a method such as gas atomization.

Next, the present invention will be described in more detail using examples. However, the examples described below are examples of embodiments of the present invention and do not limit the present invention.

Example 1
Titanium alloy materials Nos. 1 to 36 were manufactured by directed energy deposition (WAAM) or powder bed fusion using titanium alloy wire as the raw material. Specifically, in the manufacturing by directed energy deposition, titanium alloy wire (φ1.6 mm) having the chemical composition shown in Table 1 was prepared as the titanium alloy raw material.
In Examples Nos. 1-22 and 27-33, a plasma welding torch was used for additive manufacturing, with a current value of 200 A. The substrate was a titanium alloy plate with a thickness of 12.7 mm. A pre-set manufacturing area on the substrate was enclosed in a chamber and shielded with Ar gas at a flow rate of 15 L/min. A titanium alloy wire was supplied therein at a rate of 200 mm/min, melted using a plasma welding torch, and then solidified on the substrate. The cooling rate for the titanium alloy substrate temperature range of 1000-700°C was 10°C/sec. The cooling rate for temperatures below 700°C was 2°C/sec. By repeating this process multiple times, a titanium alloy material consisting of an additive manufacturing sample measuring 18 mm in width, 100 mm in length, and 15 mm in thickness was produced on the substrate.

Examples Nos. 23 to 26 are examples in which titanium alloy materials were produced by electron beam irradiation. A wire rod with a diameter of 1.6 mm was used as the titanium alloy material. The electron beam current was 50 mA, and the feed rate of the titanium alloy material was 300 mm/min. The thickness of the titanium alloy substrate was 12.7 mm, and the cooling rate in the temperature range of the titanium alloy substrate from 1000 to 700°C was 5°C/sec, and the cooling rate in the range below 700°C was 2°C/sec. The pressure of the electron beam irradiation atmosphere was (1×10 ⁻² ) Pa.

Examples Nos. 34 to 36 are examples using the powder bed fusion method. Titanium alloy powder having the chemical composition shown in Table 1, an average particle size of 30 μm, and a standard deviation of 8 μm was spread to a thickness of 30 μm to form a powder bed. A laser beam was irradiated onto the surface of the powder bed in an argon atmosphere. The heat input of the laser beam was 19.5 J/ ^mm3 , the scanning speed of the laser beam was 650 mm/sec, and the laser output was 95 W. The laser beam diameter was 50 μm. The irradiation interval of the laser beam was 100 μm. The penetration depth was 75 μm.

Next, a layer of the titanium alloy powder was laid on top of the powder bed after laser beam irradiation to create a new powder bed, and the surface of this new powder bed was irradiated with the laser beam under the same atmosphere and conditions as above. This process was repeated multiple times to produce a titanium alloy material consisting of an additive manufacturing sample measuring 18 mm wide, 100 mm long, and 15 mm thick.

For Nos. 37 and 38, 200 kg ingots were forged and processed into billets with a diameter of 100 mm, which were then heated to 950°C and hot rolled to a diameter of 32 mm to obtain round bars.

For Nos. 39 and 40, a 200 kg ingot was forged and processed into a φ100 mm billet, which was then heated to 950°C and hot-rolled to a φ32 mm round bar. The round bar was heated at 950°C for 1 hour and then air-cooled.

For Nos. 41 to 43, titanium alloy materials consisting of additively manufactured samples measuring 18 mm in width, 100 mm in length, and 30 mm in height were fabricated on a substrate using the same method as above. The titanium alloy materials were heated to 950°C and then reduced to a height of 15 mm at a strain rate of 0.5/s. They were then heated to 1100°C, held there for 10 minutes, and then water-cooled. The cooling rate during water-cooling in the range of 1000 to 700°C was approximately 5°C/s.

No. 44 was prepared on a substrate using the same method as above, consisting of an additively manufactured titanium alloy sample measuring 18 mm in width, 100 mm in length, and 30 mm in height. The titanium alloy sample was heated to 950°C and then reduced to a height of 15 mm at a strain rate of 0.5/sec. The sample was then heated to 1100°C, held there for 10 minutes, and then furnace-cooled. The cooling rate during furnace cooling in the range of 1000 to 700°C was approximately 0.1°C/sec.

The average length of the long axis of the ellipsoid-approximated α phase and the average aspect ratio were measured using the following method. Rectangular specimens measuring 10 mm high x 10 mm wide x 5 mm thick were prepared. The height and width directions of the rectangular specimens were aligned with the height and width directions of the titanium alloy material, respectively, and the thickness direction of the rectangular specimens was aligned with the longitudinal direction of the titanium alloy material. The rectangular specimens were prepared with a thickness of approximately 1 mm, adjusted so that the half-height and half-width positions of the rectangular specimens were aligned with the half-height and half-width positions of the titanium alloy material. The observation surface of the rectangular specimen (the surface formed by the height and width directions) was aligned with the half-long direction of the titanium alloy material. The 10 mm high x 10 mm wide surface of the rectangular specimen was used as the observation surface, and the observation surface was roughly polished using emery paper so that the observation surface was aligned with the half-long direction of the titanium alloy material. The observation surface was roughly polished and then buffed with colloidal silica to give a mirror finish. For the structure analysis, a scanning electron microscope (SEM) (JSM-7200F manufactured by JEOL Ltd.), an electron backscatter diffraction (EBSD) (VELOCITY EBSD detector manufactured by TSL Solutions Co., Ltd.), and analysis software OIM analysis V7 were used. The measurement and analysis conditions were an acceleration voltage of 15 kV, a measurement magnification of 250x, a measurement field of view of 468 μm in the X direction and 366 μm in the Y direction, and a measurement step of 0.5 μm. In OIM Analysis, the grain tolerance was set to 5°, and the major axis length and aspect ratio were determined by elliptical approximation of the shape of the crystal grains determined to be α-phase by Kikuchi pattern analysis. The average value was calculated using the Area method, which takes area into consideration. The elliptical approximation method was performed according to "Method 2 - Major = Maximum Distance, Minor = averaging scheme" described on page 442 of the OIM Analysis 7 manual. The measurement was performed with the rectangular parallelepiped test specimen centered at half the width and half the height, with the measurement field of view X direction aligned with the width direction of the rectangular parallelepiped test specimen and the measurement field of view Y direction aligned with the height direction of the rectangular parallelepiped test specimen.

The test specimens used in the Charpy impact test were as follows. The dimensions of the test specimen were 10 mm x 10 mm x 55 mm, and the specimens had a 2 mm V-notch. The longitudinal direction of the test specimen was aligned with the length direction of the titanium alloy material, so that the longitudinal direction of the test specimen was parallel to the substrate and the notch was perpendicular to the substrate. The central position (half position) of the width direction of the test specimen was aligned with the half position of the width direction of the titanium alloy material, and the test specimen was taken from a range of 5 to 25 mm in the height direction of the laminate. The Charpy impact test was performed at room temperature (25°C) in accordance with JIS Z 2242:2018. The impact test results were evaluated as an impact value (J/cm ² ) obtained by dividing the absorbed energy by the cross-sectional area of the test specimen.

Round bar specimens with a parallel section of 6.25 mm diameter x 32 mm and a gauge length of 25 mm were used for the tensile test. The longitudinal direction of the specimen was aligned with the length of the titanium alloy material so that the longitudinal direction was parallel to the substrate, and the center position (halfway point) of the width of the specimen was aligned with the halfway point of the titanium alloy material. The round bar specimens were taken from a height range of 5 to 25 mm in the laminate. The tensile test was performed at room temperature (25°C) with a tension speed of 1 mm/min up to the 0.2% proof stress measurement and 10 mm/min thereafter. Table 1 shows the chemical composition of the titanium alloy material, and Table 2 shows the results. Note that a "-" in Table 1 indicates that the alloying element was not actively included.

The results are shown in Table 2. The tensile strength TS was determined to be 900 MPa, which exceeds the tensile strength of the existing alloy Ti-3Al-2.5V (JIS type 61), and a value of 900 MPa or more was considered to be acceptable. Furthermore, the impact value CIS was determined to be 40 J/ ^cm2 or more. Furthermore, as an index of the balance between the properties of tensile strength and impact value, whether or not the following formula (1) is satisfied was used as the criterion, and a sample was considered to be acceptable when the following formula (1) was satisfied.

0.3 × TS + CIS ≧ 340 … (1)

Examples No. 1 and 2 are titanium alloy materials with a conventional Ti-Al-V chemical composition. Example No. 1 did not contain Fe or Cu, had a low impact strength (CIS), and did not satisfy formula (1) showing the relationship between strength (TS) and impact strength (CIS), resulting in undesirable characteristics. Example No. 2 also had a low Al content, did not contain Fe or Cu, and had low average major axis length and tensile strength. It also did not satisfy formula (1) showing the relationship between strength (TS) and impact strength (CIS), falling short of the acceptable range.

Example No. 3 is a Ti-Al-Fe alloy, but because it did not contain Cu and had an excessive O content, it had a low impact value and did not satisfy equation (1) showing the relationship between strength (TS) and impact value (CIS), and was therefore unsuccessful.

Example No. 4 did not contain Cu and did not satisfy formula (1), which shows the relationship between strength and impact value, and was therefore unsuccessful.

Example No. 5 had a low Al content, resulting in a low tensile strength TS and failing the test.

Examples No. 6 to 17 had a chemical composition containing Al: 4.6 to 8.0%, Fe: 0.2 to 1.5%, Cu: 0.3 to 2.0%, and O: 0.03 to 0.20%, and met all of the strength, impact value, and formula (1) showing the relationship between strength and impact value, making them pass the test.

Example No. 18 had excessive Al content and failed the impact value.

Example No. 19 had an excessive Fe content and failed the impact value.

Example No. 20 had an excessive Cu content, resulting in a low impact value and not satisfying equation (1) showing the relationship between strength and impact value, and was therefore unsuccessful.

Example No. 21 had an insufficient oxygen content, resulting in low tensile strength and failure.

No. 22 had an insufficient Fe content and an excessive O content, resulting in an unacceptable impact value.

Examples No. 23 to 25 are Ti-Al-Fe-Cu alloys further containing Sn. Examples No. 23 and No. 24 contained Al: 4.6-8.0%, Fe: 0.2-1.5%, Cu: 0.3-2.0%, O: 0.03-0.20%, and Sn: 5.0% or less. They met the strength, impact value, and formula (1) showing the relationship between strength and impact value, and were therefore acceptable. On the other hand, Example No. 25 had an excessive Sn content, and its impact value was unacceptable.

Examples No. 26 to 28 are Ti-Al-Fe-Cu alloys further containing Si. Examples No. 26 and 27 contained Al: 4.6-8.0%, Fe: 0.2-1.5%, Cu: 0.3-2.0%, O: 0.03-0.20%, and Si: 0.80% or less. They met all of the following criteria: strength, impact value, and formula (1) showing the relationship between strength and impact value, making them pass the test. On the other hand, Example No. 28 had an excessive Si content and failed the impact value test.

Examples No. 29 and 30 are Ti-Al-Fe-Cu-Si alloys containing Nb. Examples No. 29 and 30 contain Al: 4.6-8.0%, Fe: 0.2-1.5%, Cu: 0.3-2.0%, O: 0.03-0.20%, Si: 0.80% or less, and Nb: 8.0% or less. They met all of the requirements for strength, impact value, and formula (1) showing the relationship between strength and impact value, and were therefore accepted.

Examples No. 31 to 33 are Ti-Al-Fe-Cu alloys further containing Nb. Examples No. 31 and 32 contain Al: 4.6-8.0%, Fe: 0.2-1.5%, Cu: 0.3-2.0%, O: 0.03-0.20%, and Nb: 8.0% or less. They met the strength, impact value, and formula (1) showing the relationship between strength and impact value, and were therefore acceptable. On the other hand, Example No. 33 had an excessive Nb content, and its impact value was unacceptable.

Nos. 34 to 36 are examples of Ti-Al-Fe-Cu alloys that further contain Mo. Examples No. 34 and No. 35 contain Al: 4.6-8.0%, Fe: 0.2-1.5%, Cu: 0.3-2.0%, O: 0.03-0.20%, and Mo: 2.0% or less. They met the strength, impact value, and formula (1) showing the relationship between strength and impact value, and were therefore acceptable. On the other hand, Example No. 36 had an excessive Mo content, and its impact value was unacceptable.

Examples No. 37 to 40 were manufactured using inappropriate conditions, and the aspect ratio, average major axis length, tensile strength, impact value, or relationship between strength and impact value were unacceptable.

Examples No. 41 to 43 had an appropriate cooling rate of 5°C/sec in the range of 1000 to 700°C, which satisfied the aspect ratio, average major axis length, strength, impact value, and formula (1) showing the relationship between strength and impact value, making them pass. On the other hand, Example No. 44 had a cooling rate of 0.1°C/sec in the range of 1000 to 700°C, which was too slow, and failed the average major axis length, strength, and formula (1) showing the relationship between strength and impact value.

Example 2
A 200 kg ingot was forged to produce a φ100 mm billet. The φ100 mm billet was then heated to 950°C and rolled to produce a φ9.5 mm rod. The φ9.5 mm rod was repeatedly annealed at 750°C for 5 to 60 minutes and drawn using a cassette roller die or die drawing to produce a φ4.8 mm or φ1.2 mm rod. Each material was annealed at 750°C for 1 hour, then air-cooled to obtain a wire rod.

The maximum diameter of each manufactured wire was measured using the following method: the diameter of the wire was measured at two or more locations per cross section, and at two or more cross sections per lot, using a micrometer or calipers, and the maximum value was recorded as the maximum diameter.

Tensile tests were also conducted on each wire. For titanium materials with a diameter of 10 mm or more, round bar specimens with a parallel section of 6.25 mm diameter x 32 mm and a gauge length of 25 mm were used. The test was conducted at room temperature (25°C) at a tension speed of 10 mm/min.
For titanium materials with a diameter of 6 mm or more and less than 10 mm, round bar test pieces with a parallel section of 3 mm diameter and 20 mm length were used. The test was carried out at a tensile speed of 6 mm/min at room temperature (25°C).
For titanium materials with a diameter of less than 6 mm, test pieces with a gauge length of 100 mm were used without machining. The test was carried out at a tensile speed of 30 mm/min at room temperature (25°C).

In addition, Vickers hardness measurements were performed at the center of a cross section perpendicular to the long axis of each material at a load of 1 kgf (9.8 N) in accordance with JIS Z 2244:2020.

Table 3 shows the chemical composition of each titanium material, and Table 4 shows the results of tensile strength and Vickers hardness measurements. Note that a "-" in Table 3 indicates that the alloying element in question was not actively included.

As shown in Tables 3 and 4, a titanium alloy wire containing Al: 4.6% or more and 8.0% or less, Fe: 0.2% or more and 1.5% or less, Cu: 0.3% or more and 2.0% or less, O: 0.03% or more and 0.20% or less, Sn: 0% or more and 3.0% or less, Nb: 0% or more and 8.0% or less, Si: 0% or more and 0.80% or less, and Mo: 0% or more and 2.0% or less, a maximum diameter of 1.0 mm or more and 8.0 mm or less, and a tensile strength of 900 MPa or more could be produced.
Laminated materials were manufactured using wire rods Nos. 45 to 47 using a plasma welding torch. Specifically, a plasma welding torch was used, with a current value of 200 A. The substrate was a titanium alloy plate with a thickness of 12.7 mm. A pre-set build area on the substrate was enclosed in a chamber and shielded with Ar gas at a flow rate of 15 L/min. The titanium alloy wire rod prepared in Example 2 was melted using a plasma welding torch and further solidified on the substrate while being fed into the chamber at a rate of 200 mm/min. The cooling rate for the titanium alloy substrate temperature range of 1000 to 700°C was 10°C/sec. The cooling rate for temperatures below 700°C was 2°C/sec. By repeating this lamination process multiple times, a titanium alloy material consisting of an additive manufacturing sample measuring 18 mm in width, 100 mm in length, and 15 mm in thickness was manufactured on the substrate.
The aspect ratio of the α phase, the average value of the major axis length of the α phase, the tensile strength, and the impact value of each titanium alloy material were evaluated in the same manner as in Example 1. The results are shown in Table 5.

As shown in the results of Nos. 45 to 47, titanium alloy materials produced under appropriate conditions using titanium alloy wire rods containing Al: 4.6% or more and 8.0% or less, Fe: 0.2% or more and 1.5% or less, Cu: 0.3% or more and 2.0% or less, O: 0.03% or more and 0.20% or less, Sn: 0% or more and 3.0% or less, Nb: 0% or more and 8.0% or less, Si: 0% or more and 0.80% or less, and Mo: 0% or more and 2.0% or less, the balance being Ti and impurities, and having a maximum diameter of 1.0 mm or more and 8.0 mm or less and a tensile strength of 900 MPa or more, all satisfied the strength, impact value, and formula (1) showing the relationship between the strength and impact value, and were accepted.
On the other hand, Nos. 48 and 49 had wire diameters that were too large to achieve uniform melting, and a laminate could not be produced.

Claims (7)

In mass%,
Al: 4.6% or more and 8.0% or less,
Fe: 0.2% or more and 1.5% or less,
Cu: 0.3% or more and 2.0% or less,
O: 0.03% or more and 0.20% or less,
Sn: 0% or more and 3.0% or less,
Nb: 0% or more and 8.0% or less,
Si: 0% or more and 0.80% or less, and Mo: 0% or more and 2.0% or less,
and the balance being Ti and impurities,
At least some of
The metal structure includes an α phase and a β phase, the average length of the major axis of the α phase approximated to an ellipse is 20 μm or more and 80 μm or less, and the average aspect ratio of the α phase is 3.0 or more and 5.0 or less,
The impact value CIS, which is the value obtained by dividing the impact absorption energy obtained in a Charpy test at 25 ° C. by the cross-sectional area of the test piece, is 40 J / cm ² or more,
The tensile strength TS is 900 MPa or more,
A titanium alloy material, wherein the impact value CIS and the tensile strength TS satisfy 0.3 x TS + CIS ≥ 340. The titanium alloy material described in claim 1 contains, by mass%, one or more elements selected from the group consisting of Sn: 0.2% or more and 3.0% or less, Nb: 0.2% or more and 8.0% or less, Si: 0.20% or more and 0.80% or less, and Mo: 0.2% or more and 2.0% or less. A titanium alloy wire for producing the titanium alloy material according to claim 1,
In mass%,
Al: 4.6% or more and 8.0% or less,
Fe: 0.2% or more and 1.5% or less,
Cu: 0.3% or more and 2.0% or less,
O: 0.03% or more and 0.20% or less,
Sn: 0% or more and 3.0% or less,
Nb: 0% or more and 8.0% or less,
Si: 0% or more and 0.80% or less, and Mo: 0% or more and 2.0% or less,
and the balance being Ti and impurities,
A titanium alloy wire having a maximum diameter of 1.0 mm or more and 8.0 mm or less and a tensile strength of 900 MPa or more. A titanium alloy powder for producing the titanium alloy material according to claim 1,
In mass%,
Al: 4.6% or more and 8.0% or less,
Fe: 0.2% or more and 1.5% or less,
Cu: 0.3% or more and 2.0% or less,
O: 0.03% or more and 0.20% or less,
Sn: 0% or more and 3.0% or less,
Nb: 0% or more and 8.0% or less,
Si: 0% or more and 0.80% or less, and Mo: 0% or more and 2.0% or less,
and the balance being Ti and impurities,
The average particle size is 10 μm or more and 100 μm or less,
A titanium alloy powder having a standard deviation of particle size of 5 μm or more and 15 μm or less. A method for producing the titanium alloy material according to claim 1, comprising the steps of:
a first step of spreading titanium alloy powder containing, by mass%, Al: 4.6% to 8.0%, Fe: 0.2% to 1.5%, Cu: 0.3% to 2.0%, O: 0.03% to 0.20%, Sn: 0% to 3.0%, Nb: 0% to 8.0%, Si: 0% to 0.80%, and Mo: 0% to 2.0%, with the balance being Ti and impurities, in a layered form to form a powder bed, and irradiating a surface of the powder bed with a high-energy beam to melt and solidify a portion of the powder bed;
a second step of laying the titanium alloy powder in a layer on the powder bed to form a new powder bed, and irradiating a surface of the new powder bed with a high-energy beam to melt and solidify a portion of the new powder bed;
A method for producing a titanium alloy material, wherein the second step is repeated at least once after the first step is performed. A method for producing the titanium alloy material described in claim 1, comprising: supplying a titanium alloy material in the form of powder or wire rod containing, by mass%, Al: 4.6% to 8.0%, Fe: 0.2% to 1.5%, Cu: 0.3% to 2.0%, O: 0.03% to 0.20%, Sn: 0% to 3.0%, Nb: 0% to 8.0%, Si: 0% to 0.80%, and Mo: 0% to 2.0%, with the balance being Ti and impurities, onto a substrate; and irradiating the titanium alloy material with a high-energy beam to melt and solidify the titanium alloy material on the substrate, thereby depositing a solidified metal on the substrate. A method for producing titanium alloy material, comprising subjecting the titanium alloy material obtained by the method for producing titanium alloy material described in claim 5 or 6 to one or more of hot working, cold working, straightening, and cutting.