Titanium alloy laminated compact, its manufacturing method and raw materials

Abstract

This titanium alloy laminate molded article contains 5.50-6.75 wt% of Al, 3.50-4.50 wt% of V, not more than 0.20 wt% of O, not more than 0.40 wt% of Fe, not more than 0.015 wt% of H, not more than 0.08 wt% of C, not more than 0.05 wt% of N, and unavoidable impurities, and is characterized in that the number of pores included therein is less than 0.02 pores / mm2.

Description

[Technical Field]

[0001] The present invention relates to a titanium alloy laminate formed body with high integrity, high density, and no pressure leakage, and a method for manufacturing the same. In particular, the present invention relates to a titanium alloy laminate formed body that is formed by metal lamination molding and has high integrity without undergoing HIP (Hot Isostatic Pressing) treatment, as well as a manufacturing method and raw materials for the same. [Background technology]

[0002] Titanium alloys are lightweight yet have high tensile strength, and have been widely used in aircraft parts, etc. In this case, titanium alloys are usually cast and then processed, such as by rolling. Meanwhile, metal additive manufacturing has recently been attracting attention as a manufacturing method that uses metal powder as raw material, lays it out layer by layer, and then irradiates it with a laser or electron beam to heat, melt, and solidify only specific areas, thereby creating products in their final shape without using a mold.

[0003] Titanium alloys are also suitable for such metal lamination methods, and laminated compacts obtained by the metal lamination method exhibit high tensile strength equivalent to or greater than that of compacts obtained by casting and rolling, without the need for rolling or other processes (see Non-Patent Document 1). When a metal laminate is formed by irradiating electron beams with metal powder / plasma atomized powder manufactured by Arcam AB as raw material, the as-built material has low fatigue strength. However, it has been reported that high-quality properties can be obtained and fatigue strength is also improved by HIP-treating the as-built material (see Non-Patent Document 2).

[0004] In addition, the fatigue strength of the laminated material of the laminated compacts formed by the electron beam method using plasma atomized powder and the laser method using gas atomized powder was investigated (10 7The fatigue strengths of these steels are low at 240 MPa and 300 MPa, respectively, but it has been reported that HIP treatment reduces the pore size to about 1 / 50, and the fatigue strength of both steels increases to 580 MPa (see Non-Patent Document 3). Furthermore, in metal powders obtained by gas atomization using argon gas (free fall method / see Non-Patent Document 4, PIGA method [Plasma melting induction guiding gas atomization] / see Non-Patent Document 5), it is known that the larger the particle size of the powder particles, the higher the proportion of particles with a high pore volume fraction, and that the pores contain a large amount of argon gas.

[0005] Furthermore, it is known that metal powders produced by the rotating electrode method contain fewer particles containing pores compared to gas atomized powders and plasma gas atomized powders, but the larger the powder particle size, the larger the pore volume fraction (see, for example, Non-Patent Document 6). These phenomena in rapidly solidified powders are thought to be due to the fact that the larger the particle size of the droplets scattered during powder production, the more likely they are to deform, and therefore the more likely they are to enclose inert gases present in the environment during powder production.

[0006] Metal laminate compacts formed by electron beam or laser using atomized powder (hereinafter, atomized powder is a general term for gas atomized powder, plasma atomized powder, centrifugal atomized powder, etc.), which is a typical example of the rapidly solidified powder disclosed in the above-mentioned non-patent literature, generally exhibit excellent properties.

[0007] For example, the titanium alloy laminate disclosed in Non-Patent Document 1 exhibits high tensile properties and high elongation that are equal to or higher than those of rolled or forged materials obtained by conventional manufacturing methods. Furthermore, when comparing the tensile strength of the metal laminates made from atomized powders described in Non-Patent Documents 2 and 3 between as-laminated materials and HIP-treated materials, there are significant differences in tensile strength, yield strength, and elongation. That is, compared to as-laminated materials, the HIP-treated materials have no internal defects and have improved elongation, but their tensile strength and yield strength are somewhat lower. Furthermore, because HIP processing is performed under high temperatures and high pressures, there is a problem in that the processing costs for the laminate are high, which in turn increases the product cost. Furthermore, it is known that when HIP-treated materials are heat-treated, the defects that were reduced by HIP processing expand again, resulting in a decrease in quality. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] Mitsuru Adachi et al.: Light Metals, 66(2016), 360-367 [Non-patent document 2] Xiaoli Shui etc:Materials Science &Engineering A 680(2017),239-248 [Non-patent document 3] Tono Shotaro et al.: Powder and Powder Metallurgy, 61(2014), 250-254 [Non-patent document 4] R.Gering etc:Materials Science &Engineering A 252(1998),239-247 [Non-Patent Document 5] G.Chen etc:Powder Technology 330(2018)425-430 [Non-patent document 6] G,Chen etc: Powder Technology 333(2018)38-46 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention was developed based on the above background. Specifically, because metal laminates have a rapidly solidified structure, they exhibit a fine structure not obtainable by conventional methods, resulting in high tensile strength. Furthermore, dense products can be produced. However, even when rapidly solidified powders, such as atomized powders, are additively manufactured using a rapid solidification method, the presence of interconnected pores in the metal laminate can lead to fatal air leakage defects in thin, complex-shaped products that require dense construction. HIP treatment is effective in preventing this. However, HIP treatment, which is required to completely eliminate defects, is costly, and defects expand again after heat treatment. Therefore, it is desirable to obtain high quality without HIP treatment.

[0010] In view of the above, the object of the present invention is to provide a high-quality titanium alloy laminated compact that does not require HIP treatment and further enhances the inherently high soundness of the laminated compact, and that is low-cost and does not leak pressure even when it is a thin product with a complex shape, as well as a manufacturing method and raw materials for the same.

[0011] The soundness is the content rate of pores per unit area contained in the metal laminate. Incidentally, the as-built HIP processed material of the laminated compact made from atomized powder has a high soundness, with a typical defect count per unit area of ​​0.01 / mm. 2 The size is on the order of 10 μm, which can be observed under an optical microscope. [Means for solving the problem]

[0012] In order to solve the above problems, a first aspect of the present invention is a titanium alloy laminate compact containing 5.50 to 6.75 wt% Al, 3.50 to 4.50 wt% V, 0.20 wt% or less O, 0.40 wt% or less Fe, 0.015 wt% or less H, 0.08 wt% or less C, 0.05 wt% or less N, and inevitable impurities, and having a pore content of 0.02 pores / mm 2 The present invention provides a titanium alloy laminate compact characterized by having a thickness of less than 1 / 2 mm. The titanium alloy laminate compact according to the first aspect includes a thin wall portion at least in part, and the pore content in at least the thin wall portion is 0.02 pores / mm 2 The thickness of the thin portion is 3 mm or less, more specifically, 0.5 mm or more and 3 mm or less.

[0013] A second aspect of the present invention provides a method for producing a titanium alloy laminate formed body, characterized by laminate forming, by a metal deposition method, titanium alloy powder containing 5.50 to 6.75 wt% Al, 3.50 to 4.50 wt% V, 0.20 wt% or less O, 0.40 wt% or less Fe, 0.015 wt% or less H, 0.08 wt% or less C, 0.05 wt% or less N, and unavoidable impurities, and in which the proportion of fine powder of 45 μm or less is less than 2%. In the method for producing a titanium alloy laminate compact according to the second aspect of the present invention, the particle size of the titanium alloy powder can be set to, for example, 250 μm or less.

[0014] A third aspect of the present invention provides a titanium alloy powder for producing a titanium alloy laminate compact, comprising 5.50 to 6.75 wt. % Al, 3.50 to 4.50 wt. % V, 0.20 wt. % or less O, 0.40 wt. % or less Fe, 0.015 wt. % or less H, 0.08 wt. % or less C, 0.05 wt. % or less N, and unavoidable impurities, and in which the proportion of fine powder of 45 μm or less is less than 2%. The particle size of the titanium alloy powder according to the third aspect of the present invention can be set to, for example, 250 μm or less. [Effects of the Invention]

[0015] According to the present invention, a high-quality, thin (e.g., 3 mm or less) titanium alloy laminate compact is provided that is low-cost and free of pressure leakage, while taking advantage of the high soundness characteristic of the laminate compact, and does not require HIP treatment, and a method for manufacturing the same is provided. In particular, according to the present invention, there are almost no pores like in HIP-treated materials (the typical number of defects per unit area is 0.005 / mm 2 Although it is not the case that the pore content is less than 0.02 pores / mm 2By suppressing the temperature to less than 1000°C, it is possible to obtain a titanium alloy laminated compact that exhibits soundness without pressure leakage, similar to that of a HIP-treated material. Furthermore, according to the present invention, titanium alloy powder in which the ratio of fine particles of 45 μm or less is less than 2% is laminated by metal lamination molding, and the pore content is reduced to 0.02 pieces / mm 2 This provides a method for producing a titanium alloy laminate formed body that can suppress pressure leakage to less than 3 mm, and that exhibits soundness without pressure leakage even when the thickness is as thin as 3 mm or less. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing an electron beam lamination molding apparatus. [Figure 2] FIG. 1 is a diagram showing the state of pores. [Figure 3] FIG. 10 is a diagram showing pores observed on the polished surface. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail. As mentioned above, the metal laminate compact has a rapidly solidified structure and exhibits a fine structure that cannot be obtained by conventional methods. In addition, since it is a sound product with few pores, it exhibits high tensile strength. Here, the timing of pore formation in the laminate can be considered to be the following two cases. The first type of pores occurs during lamination. In this case, two further reasons can be considered. First, a) pores caused by unmelted powder due to improper lamination conditions are considered. In this case, it is not just a single particle that remains unmelted, but rather complex and coarse pores are formed. In addition, b) pores may be caused by gas entrapment in the laser method, which mainly uses inert gas in the environment inside the equipment. Pores in a) can be resolved by optimizing the molding conditions during lamination. Pores in b) can be resolved by using the electron beam method, which is performed in a vacuum atmosphere and therefore prevents gas entrapment.

[0018] The second type of pores occurs before lamination molding. Pores are already present in the raw powder obtained by atomization. Gas enclosed in droplets dispersed during the production of the raw powder becomes entrained within the powder, and once entrained, it finds its way into the laminated compact regardless of the lamination molding conditions. It is easy to see that managing large particle size powder is important in order to reduce the adverse effects of such gas entrainment and produce a dense, high-quality laminate.

[0019] However, the present invention has unexpectedly discovered that, unlike high-quality laminates obtained by HIP-processing the entire laminate, a sound laminate without pressure leakage in the thin-walled portions of the laminated material as is requires not only an upper limit on the powder particle size but also a reduction in the fine powder content. That is, regardless of the powder production method, reducing the fine powder content is effective in improving the compactness of the laminated material. This is likely because, even if the gas pores contained in the fine powder are small, they expand during the lamination process when the fine powder melts and solidifies, and multiple gas pores connect, causing pressure leakage. Furthermore, fine powder may promote pore formation by preventing stable and uniform dissolution during lamination.

[0020] The present invention has discovered that limiting the content of fine powder of 45 μm or less to less than 2% for powders produced by methods such as plasma atomization and rotating electrode method, which are used as rapidly solidified powders for laminate molding, is effective in improving the density of laminate molded bodies. Furthermore, even in titanium alloy powders produced by the rotating electrode method, which has few pores in the powder particles, limiting the mixing ratio of fine powder was effective in improving density and reducing pressure leakage. When considering repeated powder use, it is thought that this is because, in the case of fine powders of 45 μm or less in an air atmosphere, defects may occur due to the increase in the oxide film caused by the large specific surface area.

[0021] The titanium alloy laminate compact according to one embodiment of the present invention is obtained by laminating titanium alloy powder. Powder bed fusion can be used as the lamination method. Powder bed fusion is a method in which raw metal powder is laid out layer by layer, and then irradiated with an electron beam to melt and solidify only specific portions, resulting in lamination. The obtained laminated compact has a composition containing 5.50 to 6.75 wt % Al, 3.50 to 4.50 wt % V, 0.20 wt % or less O, 0.40 wt % or less Fe, 0.015 wt % or less H, 0.08 wt % or less C, 0.05 wt % or less N, and unavoidable impurities.

[0022] This titanium alloy laminated compact has a pore content of 0.02 pores / mm 2 Less than 0.02 pieces / mm 2 If pores exceeding this number are present in the laminated molded product, the pores will be more likely to connect with each other, resulting in a decrease in density and pressure leakage defects in thin-walled laminated products. Note that "thin" here is defined as 3 mm or less, and more specifically, 0.5 mm to 3 mm or less as a "thin product" or "thin-walled portion." Therefore, the pore content of at least the thin-walled portion of a laminated molded product having at least a thin-walled portion of 0.5 mm to 3 mm is 0.02 pores / mm 2 The pore content must be less than 0.02 / mm2 where the thickness of the laminate exceeds 3 mm. 2 On the other hand, for products with a thickness of less than 0.5 mm, the pore content is 0.02 / mm 2 Even if the thickness is less than this, it is not easy to produce a leak-proof product using currently available equipment. Therefore, the product thickness range for limiting the pore content to obtain a leak-proof laminate is 0.5 mm or more and 3 mm or less.

[0023] A method for producing a titanium alloy laminate compact according to a second embodiment of the present invention comprises laminating titanium alloy powder by metal lamination molding. The titanium alloy powder used as a raw material has a composition containing 5.50 to 6.75 wt% Al, 3.50 to 4.50 wt% V, 0.20 wt% or less O, 0.40 wt% or less Fe, 0.015 wt% or less H, 0.08 wt% or less C, 0.05 wt% or less N, and unavoidable impurities.

[0024] Furthermore, the proportion of fine particles of 45 μm or less in the titanium alloy powder used as the raw material is less than 2%. Not only are pores likely to be found in the coarse powder in titanium alloy powders, but fine powder of 45 μm or less cannot be ignored, and their proportion is a factor that has a significant impact on the density after metal lamination. The pores in conventional titanium alloy powders remain in the laminated compacts made by laminating titanium alloy powders. Therefore, if the proportion of fine powder of 45 μm or less in titanium alloy powder exceeds a certain value, the pores in the laminated compacts will connect, causing pressure leaks. Therefore, the proportion of fine powder of 45 μm or less in titanium alloy powders is less than 2%.

[0025] As mentioned above, the content of fine particles in the titanium alloy powder has been considered from the viewpoint of the quality of the laminate. In addition to quality, in the case of an electron beam lamination apparatus, the atmosphere inside the apparatus is a vacuum, so consideration is also given to preventing the titanium alloy powder from being sucked into the apparatus and causing a breakdown in the vacuum system of the apparatus.

[0026] On the other hand, the larger the powder size during powder production, the more pores will be trapped in the powder. Therefore, the maximum particle size is preferably 250 μm, more preferably 150 μm. Furthermore, the larger the particle size of the titanium alloy powder particles, the rougher the surface of the laminated compact will be. In this sense, the maximum particle size of the titanium alloy powder particles is preferably 250 μm, more preferably 150 μm.

[0027] The titanium alloy powder described above is molded by metal lamination, which includes electron beam lamination and laser lamination. Generally, electron beam lamination is widely used, and is carried out using the electron beam lamination apparatus shown in FIG. 1 through the following steps. (1) A layer of metal powder of a certain thickness is spread over the entire surface. (2) The electron beam is irradiated locally at the location where the metal powder layer is to be solidified, heating the powder layer and instantly melting and solidifying the powder. In this case, the electron beam is scanned based on the 3D data slice data. (3) The manufacturing table is lowered and another layer of metal powder is laid down. (4) The above steps are repeated to sequentially stack the metals, and after obtaining a laminated green body in its final shape, the unsolidified powder is removed to obtain the laminated green body. By subjecting the titanium alloy powder to the above steps, a titanium alloy laminate compact having a predetermined shape can be obtained.

[0028] The electron beam deposition apparatus has the structure shown in Fig. 1 and includes an electron gun 1, a focus coil 6, a deflection coil 7, and a vacuum chamber 9, with the inside of the apparatus maintained at a vacuum. The electron gun 1 includes a filament 2 that emits electrons, a grid cup 3 that extracts the electrons, and an anode 4 that accelerates the electrons. In the electron gun 1, electrons are extracted by a grid cup 3 from a filament 2 heated to over 2500°C, accelerated to half the speed of light through an anode 4, and irradiated as an electron beam 8 onto a layer of metal powder 11. The metal powder 11 is, for example, titanium powder with a particle size of 65 μm, and is contained on a manufacturing table arranged in a vacuum chamber 9. At this time, the electron beam 8 is focused on the metal powder 11 by a focus coil 6, and is scanned into a predetermined shape by a deflection coil 7 based on 3D data and slice data.

[0029] When the electron beam 8 is irradiated onto the layer of metal powder 11, its kinetic energy is converted into heat, which heats and melts the metal powder, and then it is rapidly solidified. Further layers of metal powder 11 are laid on top of that, and the same process is repeated, stacking the metal and forming the final product into the desired shape. [Example]

[0030] Examples of the present invention will be described below in comparison with comparative examples. Ti-6%Al-4%V titanium alloy powders with particle sizes of 30 μm to 210 μm were produced by rotating electrode deposition or plasma atomization, and were classified into six types of titanium alloy powders with different content ratios of fine powder of 45 μm or less by classification. Of these, powders with a ratio of fine powder of 45 μm or less of 0.5%, 1.5%, and 1.3% were designated Examples 1, 2, and 3, respectively, and powders with a ratio of fine powder of 45 μm or less of 2.4%, 3.3%, and 4.2%, respectively. These six types of titanium alloy powders were then used to form a 20 mm × 20 mm × 20 mm first metal laminate compact for observing the amount of pores generated and a second metal laminate compact for evaluating pressure leakage by electron beam deposition. The second metal laminate compact was made into the following four types of cylindrical laminates. (1) Total length 100mm, outer diameter 18mm, inner diameter 13mm, thickness 2.5mm (2) Total length 100mm, outer diameter 16mm, inner diameter 10mm, thickness 3mm (3) Total length 100mm, outer diameter 18mm, inner diameter 10mm, thickness 4mm (4) Total length 100mm, outer diameter 18mm, inner diameter 16.8mm, thickness 0.6mm

[0031] Of the pores appearing in the first metal laminate compact, cavities of 50 μm or larger were counted as pores that reduce the soundness of the metal laminate compact, as shown in Figure 3. As a result, on the 20 mm × 20 mm observation surface of the first metal laminate compact, 13 pores were confirmed in Comparative Example 2 as shown in Figure 2(a), 3 pores in Example 3 as shown in Figure 2(b), and 1 pore in Example 1 as shown in Figure 2(c). Regarding pressure leakage, when a cylindrical laminate (second metal laminate molding) with one end closed was placed in water, 1 MPa of nitrogen gas was sealed inside the laminate, and pressure was applied for one minute, it was determined that a pressure leak had occurred when bubbles emerged from the water.

[0032] Table 1 shows the effect of the proportion of fine powder on the soundness (pore content) of the metal laminate compact obtained from the above observation results.

[0033] [Table 1]

[0034] The results shown in Table 1 make the following clear: First, in Examples 1 to 3 in which the proportions of fine powder of 45 μm or less were 0.5%, 1.5%, and 1.3%, respectively, the soundness (pore content) in the first metal laminate compact was 0.0025 pieces / mm 2 , 0.005 pieces / mm 2 and 0.015 pieces / mm 2 In Examples 1 to 3, no pressure leakage occurred in any of the second metal laminate molded bodies having thicknesses of 3 mm, 2.5 mm, 4.0 mm, and 0.6 mm.

[0035] In Examples 1 to 3, the pore content in the metal laminate compact was 0.02 pores / mm 2 The reason for the low value of less than 2% is that for both the plasma gas atomized powder and the rotating electrode powder used as raw materials, the powder manufacturing conditions were set and the fine powder of 45 μm or less was classified to reduce the value to less than 2%.

[0036] In contrast, in Comparative Examples 1 to 3, in which the proportions of fine powder of 45 μm or less were 2.4%, 3.3%, and 4.2%, respectively, the pore contents in the first metal laminate compact were 0.0225 pores / mm 2 , 0.0325 pieces / mm 2 and 0.0375 pieces / mm 2 Both are 0.02 pieces / mm 2 Therefore, pressure leakage occurred in the second metal laminate moldings with thicknesses of 3 mm, 2.5 mm, and 0.6 mm. However, no pressure leakage occurred in the second metal laminate molding with a thickness of 4 mm.

[0037] From the above, it can be concluded that a titanium alloy metal laminate compact having a thin-walled portion with a thickness of 3 mm or less, more specifically, a thickness of 0.5 mm or more and 3 mm or less, has a pore content of 0.02 pores / mm 2 It was found that if the thickness is less than 1 / 2 mm, pressure leakage does not occur in the thin-walled portion. It was also found that if the ratio of fine powder of 45 μm or less contained in the raw material titanium alloy powder is less than 2.0%, the pressure leakage at the thin-walled portion described above does not occur.

[0038] Although the above embodiment has been described with reference to a metal lamination method using an electron beam, it goes without saying that the present invention can also be applied to a metal lamination method using a laser beam.

Claims

1. A titanium alloy laminate compact having a thickness of 0.5 mm or more, containing 5.50 to 6.75 wt% Al, 3.50 to 4.50 wt% V, 0.20 wt% or less O, 0.40 wt% or less Fe, 0.015 wt% or less H, 0.08 wt% or less C, 0.05 wt% or less N, and inevitable impurities, with the balance being Ti, wherein the content of pores of 50 μm or more is 0.02 / mm ２ A titanium alloy laminate formed body characterized in that it is less than.

2. A titanium alloy laminate compact containing 5.50 to 6.75 wt. % Al, 3.50 to 4.50 wt. % V, 0.20 wt. % or less O, 0.40 wt. % or less Fe, 0.015 wt. % or less H, 0.08 wt. % or less C, 0.05 wt. % or less N, and inevitable impurities, with the balance being Ti; At least a part of the thin-walled portion has a thickness of 0.5 mm or more and 3 mm or less, The content of pores of 50 μm or more in the thin-walled portion is 0.02 pieces / mm ２ A titanium alloy laminate formed body characterized in that it is less than.

3. % of V, 0.20 wt % or less of O, 0.40 wt % or less of Fe, 0.015 wt % or less of H, 0.08 wt % or less of C, 0.05 wt % or less of N, and unavoidable impurities, with the balance being Ti, wherein the titanium alloy powder has a particle size of 210 μm or less and includes fine powder having a particle size of 45 μm or less, and the mass ratio of the fine powder having a particle size of 45 μm or less in the titanium alloy powder is less than 2%, the method for producing a titanium alloy laminate compact comprising laminating and molding the titanium alloy powder by a metal lamination method.

4. 1. A titanium alloy powder for producing a titanium alloy laminate compact, comprising 5.50 to 6.75 wt. % Al, 3.50 to 4.50 wt. % V, 0.20 wt. % or less O, 0.40 wt. % or less Fe, 0.015 wt. % or less H, 0.08 wt. % or less C, 0.05 wt. % or less N, and inevitable impurities, with the balance being Ti, the titanium alloy powder having a particle size of 210 μm or less and including fine powder having a particle size of 45 μm or less, the mass ratio of the fine powder having a particle size of 45 μm or less in the titanium alloy powder being less than 2%.

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