Titanium alloy powder

Abstract

We provide titanium alloy powder with excellent fluidity. [Solution] A titanium alloy powder containing 5.0 to 7.0 mass% of Al, wherein the standard deviation of the surface Al concentration of the titanium alloy particles, determined by Auger electron spectroscopy analysis of a plurality of titanium alloy particles constituting the powder, is 0.40 mass% or more.

Description

Technical Field

[0001] The present disclosure relates to titanium alloy powder.

Background Art

[0002] Titanium alloys such as Ti-6Al-4V are used in the aircraft industry, medical supplies, etc. because they exhibit lightweight, high strength, high corrosion resistance, etc. In manufacturing parts and the like for these applications, titanium alloy powder is used, and for example, additive manufacturing, metal powder injection molding, thermal spraying, etc. are performed. As a melting method for refractory reactive metals such as titanium, for example, in Patent Document 1, in a consumable electrode type vacuum arc melting method, a water-cooled copper crucible is formed in a prismatic shape with R provided at the four corners, and the inner surface of the crucible is lined with a refractory such as a CaO-based, ZrO2-based, TiO2-based, Al2O3-based refractory, and a magnetic field of 5 to 75 gauss is applied in the vertical direction inside the crucible during electrode melting. A method for manufacturing a rectangular ingot by a consumable electrode type vacuum arc melting method is shown. Further, as a method for manufacturing titanium alloy powder with reduced impurity incorporation and increased yield of refractory reactive metals such as titanium obtained in Patent Document 1, Patent Document has a first melting step of melting a molded body obtained by compressing a mixed powder containing titanium powder and metal element powder other than titanium to obtain a first molten metal, an ingot manufacturing step of injecting the first molten metal into a mold and solidifying the first molten metal to manufacture an ingot, a second melting step of melting the ingot in an inert gas atmosphere to obtain a second molten metal, and a powdering step of powdering the second molten metal with a gas atomizing device. A method for manufacturing titanium alloy powder is shown.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

[0004] When using titanium alloy powder in additive manufacturing and other processes as described above, excellent fluidity is required for the titanium alloy powder. Regarding titanium alloy powder, Patent Document 2 shows a method for producing titanium alloy powder that can improve yield and reduce environmental impact, but the fluidity of the titanium alloy powder has not been considered. This disclosure has been made in view of these circumstances, and its purpose is to provide titanium alloy powder with excellent fluidity. [Means for solving the problem]

[0005] One aspect of the present invention is: A titanium alloy powder containing 5.0 to 7.0 mass% of Al, The titanium alloy powder is characterized in that the standard deviation of the surface Al concentration of the titanium alloy particles, as determined by Auger electron spectroscopy analysis of the multiple titanium alloy particles constituting the powder, is 0.40 mass% or more.

[0006] Aspect 2 of the present invention is, Furthermore, the titanium alloy powder described in Embodiment 1 is a titanium alloy powder containing 3.0 to 6.0 mass% of V. [Effects of the Invention]

[0007] According to this disclosure, it is possible to provide titanium alloy powder with excellent fluidity. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view illustrating the AES (Auger electron spectroscopy) measurement method. [Modes for carrying out the invention]

[0009] The inventors diligently studied to obtain a titanium alloy powder with excellent fluidity and found that a titanium alloy powder containing 5.0 to 7.0 mass% of Al is sufficient, provided that the standard deviation of the surface Al concentration of the titanium alloy particles, as determined by Auger electron spectroscopy analysis of the multiple titanium alloy particles constituting the powder, is 0.40 mass% or more. The titanium alloy powder according to this embodiment will be described below.

[0010] The titanium alloy powder according to this embodiment is a titanium alloy powder containing a predetermined amount of Al, and the standard deviation of the surface Al concentration of multiple titanium alloy particles constituting the titanium alloy powder, as determined by Auger electron spectroscopy, varies by 0.40 mass% or more. The inventors investigated and found that increasing the variation in surface Al concentration among titanium alloy particles contributes to improving the fluidity of the titanium alloy powder. The detailed mechanism has not been fully elucidated, and the present invention is not bound by any theory, but it is thought to be as follows. That is, the variation in surface Al concentration among titanium alloy particles also causes variation in the amount of surface hydroxyl groups (-OH) formed on the surface of each titanium alloy particle. If hydrogen bonding between these surface hydroxyl groups is the factor that generates the adhesive force between particles, then the presence of particles with a small amount of surface hydroxyl groups, i.e., particles with a small amount of hydrogen bonding, causes a decrease in the overall bonding force between particles, which is one possible reason for the improved fluidity of the titanium alloy powder.

[0011] The standard deviation of the surface Al concentration of the titanium alloy particles is preferably 0.50% by mass or more, and more preferably 0.55% by mass or more. Furthermore, from the viewpoint of the alloy composition range, the standard deviation of the surface Al concentration is preferably 2.20% by mass or less, and more preferably 1.65% by mass or less.

[0012] The standard deviation of the surface Al concentration of titanium alloy particles is determined by the method described in the examples below. The surface Al concentration of titanium alloy particles determined by Auger electron spectroscopy is not particularly limited in this embodiment. The surface Al concentration of titanium alloy particles determined by Auger electron spectroscopy may differ from the Al concentration of the titanium alloy powder, i.e., the Al concentration in all titanium alloy particles constituting the titanium alloy powder. The surface Al concentration of titanium alloy particles determined by Auger electron spectroscopy may be, for example, in the range of 3.26 to 6.56 mass%.

[0013] The chemical composition of the titanium alloy powder according to this embodiment satisfies at least an Al concentration of 5.0 to 7.0 mass%. A titanium alloy powder containing approximately 6.0 mass% Al, with an Al concentration of 5.0 to 7.0 mass%, is considered to exhibit the desired high fluidity if the standard deviation of the surface Al concentration of the multiple titanium alloy particles constituting the titanium alloy powder satisfies the above range. Examples of titanium alloys constituting the titanium alloy powder include Ti-6Al-4V containing 5.5 to 6.75 mass% Al and 3.5 to 4.5 mass% V, and Ti-6Al-4V containing 5.5 to 6.5 mass% Al and 3.5 to 4.5 mass% V. ELI contains 5.00-6.00 mass% Al, 5.00-6.00 mass% V, 1.50-2.50 mass% Sn, and 0.35-1.00 mass% Cu. Ti-6Al-6V-2Sn contains 5.50-6.50 mass% Al, 1.80-2.20 mass% Mo, 3.60-4.40 mass% Zr, and 1.80-2.20 mass% Sn. Examples include Ti-6Al-2Sn-4Zr-2Mo-0.08Si, which contains 0.06-0.10 mass% of Si, and Ti-6Al-2Sn-4Zr-6Mo, which contains 5.50-6.50 mass% of Al, 1.75-2.25 mass% of Sn, 3.60-4.40 mass% of Zr, and 5.50-6.50 mass% of Mo. These titanium alloys may contain Fe in the range of 1.00 mass% or less, even 0.25 mass% or less, O (oxygen) in the range of 0.20 mass% or less, N (nitrogen) in the range of 0.05 mass% or less, and C (carbon) in the range of 0.08 mass% or less.

[0014] The titanium alloy powder according to this embodiment is preferably a titanium alloy powder further containing 3.0 to 6.0 mass% of V, more preferably one or more of the above Ti-6Al-4V, Ti-6Al-4V ELI, and Ti-6Al-6V-2Sn, and even more preferably Ti-6Al-4V.

[0015] The titanium alloy powder according to this embodiment is not particularly limited in size, but it is preferable that, for example, the median diameter (D50) of the volume particle size distribution is in the range of 25 μm to 35 μm.

[0016] As described above, the titanium alloy powder of the present invention exhibits excellent fluidity. The fluidity of the titanium alloy powder according to this embodiment is evaluated by the inter-powder adhesion force, as shown in the examples described later. The inter-powder adhesion force of the titanium alloy powder according to this embodiment is 95.00 Pa or less, as measured in the examples described later. The inter-powder adhesion force is preferably 90.00 Pa or less, more preferably 85.00 Pa or less, even more preferably 80.00 Pa or less, and even more preferably 75.00 Pa or less.

[0017] One method for obtaining the titanium alloy powder according to this embodiment is as follows: a rod-shaped molded body forming step in which a mixed powder containing titanium raw material powder and raw material powder of a metal element other than titanium is compressed and molded to obtain a rod-shaped molded body, The process involves inducing heating of the rod-shaped molded body using an induction heating coil to melt it and obtain a first molten metal, wherein the supply rate of the rod-shaped molded body to the induction heating coil is increased to 18 cm / min or more when the diameter of the cross-section of the rod-shaped molded body is 45 to 55 mm, as shown in the embodiment described later, to melt the rod-shaped molded body and obtain a first molten metal; An ingot manufacturing process in which the first molten metal is poured into, for example, a cylindrical mold, and the first molten metal is solidified to produce a rod-shaped ingot, A step of subjecting the rod-shaped ingot to induction heating with an induction heating coil to melt it and obtaining a second molten metal, wherein the supply rate of the rod-shaped ingot to the induction heating coil is increased to 20 cm / min or more, for example, as shown in the examples described later, when the diameter of the cross-section of the rod-shaped ingot is 45 to 55 mm, to melt the rod-shaped ingot and obtain a second molten metal; a second melting step A powdering step of powdering the second molten metal by gas atomization A method for producing titanium alloy powder including these steps will be described below.

[0018] (Rod-shaped compact forming step) A rod-shaped compact is obtained by compression molding a mixed powder containing titanium raw material powder and raw material powder of a metal element other than titanium.

[0019] As the titanium raw material powder, for example, sponge titanium raw material powder, gas atomized titanium raw material powder, etc. can be used. Sponge titanium raw material powder is very inexpensive compared to gas atomized titanium raw material powder and is economically superior. Note that the sponge titanium raw material powder is produced using the Kroll process and may slightly contain magnesium chloride (MgCl2). Also, the particle size of the titanium raw material powder is preferably within the range of 0.3 mm or more and 12.7 mm or less (referring to those that pass through a sieve with a mesh opening of 12.7 mm and remain on a sieve with a mesh opening of 0.3 mm. The same applies to the particle size of the raw material powder hereinafter), more preferably within the range of 0.4 mm or more and 3 mm or less, and particularly preferably within the range of 0.6 mm or more and 3 mm or less.

[0020] As raw material powders of metal elements other than titanium, for example, when manufacturing Ti-Al alloy powder, Al raw material powder can be used. When manufacturing Ti-6Al-4V alloy powder, examples include Al-V alloy raw material powder in which the mother alloy has a mass ratio of Al:V=6:4, or Al-V alloy raw material powder in which the mother alloy has a mass ratio of Al:V=5:5, and a mixture of at least one of Al and V raw material powders. Each raw material powder is appropriately selected according to the composition of the titanium alloy powder to be manufactured. The particle size of the raw material powder of metal elements other than titanium is preferably in the range of 0.2 mm to 50 mm (meaning particles that pass through a sieve with a mesh opening of 50 mm and remain on a sieve with a mesh opening of 0.2 mm), and more preferably in the range of 0.5 mm to 30 mm.

[0021] The method for mixing titanium raw material powder with raw material powder of metal elements other than titanium is not particularly limited, and methods such as a rotary blender can be used. Next, the mixed powder is compressed to form a rod-shaped molded body. Known methods for compression molding include die pressing and cold isostatic pressing. As shown in the examples described later, multiple molded bodies may be produced and connected by welding or the like to obtain a rod-shaped molded body.

[0022] (First melting process) The first melting step is a step in which the rod-shaped molded body is induction heated in an induction heating coil to melt it and obtain a first molten metal. In this first melting step, it is preferable to increase the supply rate of the rod-shaped molded body to the induction heating coil to 18 cm / min or more when the diameter of the cross-section of the rod-shaped molded body is 45 to 55 mm, for example, as shown in the example described later. This makes it easier for the material of the first molten metal, and by extension the ingot obtained by solidifying the first molten metal, to become non-uniform, and it is thought that titanium alloy powder can be obtained in which the standard deviation of the surface Al concentration of titanium alloy particles is above a certain value.

[0023] In the first melting step, specifically, the rod-shaped molded body is supplied from top to bottom through an induction heating coil so that it passes inside the annular induction heating coil. When the rod-shaped molded body is induction heated by the induction heating coil, it gradually melts from the bottom, and the first molten metal is continuously prepared. At this time, magnesium chloride (MgCl2) contained in the rod-shaped molded body can be evaporated and removed. Here, it is preferable that the surface temperature of the rod-shaped molded body measured with a radiation thermometer is within the range of 800°C to 1200°C. The melting point of titanium contained in the rod-shaped molded body is in the 1600°C range, but by controlling the surface temperature of the rod-shaped molded body measured with the radiation thermometer to be within the above range, the melting of the rod-shaped molded body proceeds well, and the first molten metal can be obtained. Furthermore, it is preferable to use an induction heating coil with a shape in which the diameter decreases from top to bottom.

[0024] (Ingot manufacturing process) In the ingot manufacturing process, the first molten metal is poured into, for example, a cylindrical mold, and the first molten metal is allowed to solidify to obtain a rod-shaped ingot. For example, the prepared first molten metal can be continuously flowed down into a mold (for example, a bottomed cylindrical mold with a height of 500 mm and an inner diameter of 50 mm) located below an induction heating coil. Here, the mold is cooled by water cooling, and the first molten metal poured into the mold is sequentially cooled and solidified to obtain a rod-shaped ingot.

[0025] (Second melting process) The second melting step involves inductively heating the rod-shaped ingot with an induction heating coil to melt it and obtain a second molten metal. In this second melting step, the supply rate of the rod-shaped ingot to the induction heating coil is increased to 20 cm / min or more, for example, as shown in the embodiment described later, when the diameter of the cross-section of the rod-shaped ingot is 45 to 55 mm. This is thought to produce a second molten metal with a non-uniform material, and by gas atomizing this second molten metal, a titanium alloy powder is obtained in which the standard deviation of the surface Al concentration of the titanium alloy particles is above a certain value.

[0026] In the second melting step, for example, the rod-shaped ingot is set in a gas atomizing device, and the rod-shaped ingot is melted using an induction heating coil installed in the gas atomizing device to prepare a second molten metal. The gas atomizing device is a device for producing spherical metal element powder and includes a chamber, an induction heating coil, and a gas injection nozzle.

[0027] More specifically, for example, the chamber of the gas atomizing device is replaced with an inert gas, and a rod-shaped ingot is supplied from top to bottom through the annular induction heating coil so as to pass inside the coil. The rod-shaped ingot is then induction heated by the induction heating coil, gradually melting from the bottom, and a second molten metal is continuously prepared. It is preferable to use argon (Ar) as the inert gas. It is also preferable to use an induction heating coil with a shape in which the diameter decreases from top to bottom.

[0028] (Powdering process) The second molten metal is pulverized by gas atomization. Specifically, for example, the prepared second molten metal is continuously flowed downwards within the chamber. Here, an inert gas is injected from the gas injection nozzle of the gas atomizing device, and the inert gas is blown onto the molten metal flow, causing the molten metal flow to be finely dispersed and solidified.

[0029] For gas atomization, the initial pressure of the atomizing gas should be 5-100 kgf / cm². 2 The gas flow rate per 1 kg of dissolving and dropping raw material should be 10 Nm³ 3 More than 40Nm 3 The following are some examples of things that may be done.

[0030] The method for producing the titanium alloy powder according to this embodiment is not limited to the above method, as long as it is a method that can produce the titanium alloy powder according to this embodiment. For example, instead of increasing the supply rate of the rod-shaped molded body and / or rod-shaped ingot to the induction heating coil, or in addition to increasing the supply rate, increasing the particle size of the titanium raw material powder and / or raw material powder of metal elements other than titanium is also considered to be one of the means that can increase the standard deviation of the surface Al concentration of the titanium alloy particles in the present invention. [Examples]

[0031] The present invention will be described in more detail below with reference to examples. The present invention is not limited by the following examples, and can be implemented with appropriate modifications within the scope that is consistent with the spirit described above and below, and all such modifications are included within the technical scope of the present invention.

[0032] 1. Preparation of titanium alloy powder (Example 1: Ti-6Al-4V alloy powder with an Al target value of 6.5 mass%) • Sponge titanium powder (mass: 447g, particle size: 0.3~5.6mm), and • Al-V alloy powder (master alloy with a mass ratio of Al:V = 35:65, mass: 31g, particle size: 0.2~2mm) and Al powder (mass: 22g, particle size: 0.425~0.850mm) A mixture of these materials (mass: 500g) was used as the raw material, and these were mixed to prepare a mixed powder. Next, the mixed powder was compressed using a die press to form a round bar with a diameter of 50mm and a length of 74mm. The above process was repeated to form 11 round bars (mass: 5.5kg), which were then welded together to obtain a rod-shaped molded body.

[0033] Next, the rod-shaped molded body was melted (first melting) using an induction heating coil to prepare the first molten metal. The conditions for this first melting were a current of 350A and a feed rate of the rod-shaped molded body of 18cm / min. The first molten metal was then poured into a bottomed cylindrical mold (height: 500mm, inner diameter: 50mm), and the first molten metal was allowed to solidify to produce a rod-shaped ingot.

[0034] Next, the chamber of the gas atomizer was replaced with argon (Ar), and the rod-shaped ingot was melted (second melting) using an induction heating coil installed in the gas atomizer to prepare a second molten metal. The conditions for this second melting were a current of 350A and a feed rate of 20cm / min for the rod-shaped ingot. Then, argon gas was injected from the gas injection nozzle of the gas atomizer, and an inert gas was blown onto the second molten metal that was continuously flowing downwards in the chamber to produce spherical Ti-6Al-4V alloy powder (Ti-6Al-4V gas atomized powder) with an Al target value of 6.5 mass%. The median diameter (D50) of the volume particle size distribution of the Ti-6Al-4V alloy powder obtained by classification was 30 μm.

[0035] (Example 2: Ti-6Al-4V alloy powder with an Al target value of 5.5 mass%) In the raw materials of Example 1 described above, the mass of sponge titanium raw material powder was 453g, the mass of Al-V alloy raw material powder was 30g, and the mass of Al raw material powder was 17g. Ti-6Al-4V alloy powder (Ti-6Al-4V gas atomized powder) with an Al target value of 5.5 mass% was produced in the same manner as in Example 1. The median diameter (D50) of the volume particle size distribution of the Ti-6Al-4V alloy powder obtained by classification was 31 μm.

[0036] (Comparative Example 1) A commercially available rod-shaped material of Ti-6Al-4V (dimensions: diameter (Φ) 50 mm x 500 mm) was prepared. This rod-shaped material corresponds to the rod-shaped ingot obtained after the first melting in Examples 1 and 2, but unlike the rod-shaped ingot of Examples 1 and 2, it is formed from a homogeneous material obtained through two or more melting processes.

[0037] Then, the chamber of the gas atomizer was replaced with argon (Ar), and the rod-shaped material was melted using an induction heating coil installed in the gas atomizer (corresponding to the second melting in Examples 1 and 2) to prepare molten metal. The melting conditions were set to a current of 350A and a feed rate of 14cm / min for the rod-shaped material. Then, argon gas was injected from the gas injection nozzle of the gas atomizer, and an inert gas was blown onto the molten metal that was continuously flowing downwards in the chamber to produce spherical Ti-6Al-4V alloy powder (Ti-6Al-4V gas atomized powder). The median diameter (D50) of the volume particle size distribution of the Ti-6Al-4V alloy powder obtained by classification was 26 μm.

[0038] Comparative Example 1 is an example of a conventional method for manufacturing titanium alloy powder, in which the feed rate of the rod-shaped material in the melting process is the conventional speed, that is, a slower speed than in this embodiment.

[0039] 2. Characterization of Titanium Alloy Powder (1)AES measurement (1-1) Sample preparation A carbon film was formed by applying a carbon paste evenly to a silicon wafer and drying it. Next, Ti-6Al-4V alloy powder was sprinkled onto the carbon film. Then, it was lightly pressed down using a finger through weighing paper. After that, excess powder was blown away with a blower to obtain a sample for measurement. This method has the advantage that a large amount of powder can be fixed at once. Furthermore, this method has the advantage that since no load is applied that would cause plastic deformation of the titanium alloy particles, most titanium alloy particles can be measured. The fixed Ti-6Al-4V alloy powder was then set in the analytical apparatus described later so that it could be observed.

[0040] (1-2) AES (Auger electron spectroscopy) measurement Auger electron spectroscopy analysis was performed on the titanium alloy powders (Ti-6Al-4V gas atomized powders) of Examples 1 and 2 and Comparative Example 1 using the Auger electron spectroscopy analyzer described below. As shown in Figure 1, the detector (electrostatic hemispherical electron spectrometer) 1 was installed at an angle, and the measurement was performed with the sample 5 tilted at 30° in order to efficiently detect Auger electrons 7 by irradiating the sample 5 with the electron beam 3. The resulting map (field of view size 240 μm × 240 μm, magnification 500x) is an image as if illuminated from the direction of the detector 1. In addition, oxygen mapping was obtained in advance to identify the areas where the surface of each particle was not in shadow relative to the detector 1, i.e., the areas where the surface of each particle was bright relative to the detector 1. Then, the spectra of the bright areas relative to the detector were measured for each of 12 arbitrarily selected particles within one map. In the measurement, the surface Al concentration was measured by irradiating a 5 μm × 5 μm area in the bright area of ​​one particle with the electron beam. Then, the mean and standard deviation of the surface Al concentration of the 12 titanium alloy particles were calculated from the measured values ​​of the surface Al concentration of the 12 titanium alloy particles. The results are shown in Table 1. [Details of Auger electron spectrometer] Model: JEOL (Japan Electronics Corporation) JAMP-9510F Electron gun: Thermionic field emission type Detection depth: a few nanometers or less Acceleration voltage: 10kV Irradiation current: 10nA

[0041] (2) Measurement of the adhesion force between powders Using a rotary drum type powder flowability analyzer (Revolution Powder Analyzer, Mercury Scientific Inc., Rev2015), the collapse angles of titanium alloy powders (Ti-6Al-4V gas atomized powders) from Examples 1 and 2 and Comparative Example 1 were measured, and the inter-powder adhesion force was calculated using the following formula (1) described in MZ Gao, et al., Powder Technology, Volume 383 (2021), pp. 30-42. The amount of titanium alloy powder used for measurement was 55-60 g. The measurement results are shown in Table 1.

[0042]

number

[0043] In equation (1), M (kg): Mass of powder in the drum S(m 2 ): Total area of ​​powder t(m): Drum width W(m): Length of the flow area during collapse. B(m 2 ): Area of ​​the flowing powder layer during collapse g(m·s -2 ):Gravity acceleration γ(°): Indicates the angle of collapse.

[0044] [Table 1]

[0045] As shown in Table 1, in Examples 1 and 2, the standard deviation of the surface Al concentration of the titanium alloy particles was 0.40 mass% or more, indicating variation, which resulted in low inter-powder adhesion. In contrast, in Comparative Example 1, the standard deviation of the surface Al concentration of the titanium alloy particles was kept below 0.40 mass%, resulting in high inter-powder adhesion. [Industrial applicability]

[0046] The titanium alloy powder of the present invention can be used in a wide range of applications, such as electronic components, the aerospace industry, automotive parts, civil engineering and construction materials, various tools, and medical supplies. In the manufacture of parts for these applications, it can be suitably used as a target material, a material for 3D printers, a material for metal injection molding, and so on. [Explanation of symbols]

[0047] 1. Detector (Electrostatic hemispherical electron spectrometer) 3. Electron beam 5. Sample for measurement 7 Auger Electronics

Claims

1. A titanium alloy powder containing 5.0 to 7.0% by mass of Al, A titanium alloy powder wherein the standard deviation of the surface Al concentration of multiple titanium alloy particles constituting the powder, as determined by Auger electron spectroscopy, is 0.40 mass% or more.

2. The titanium alloy powder according to claim 1, further comprising a titanium alloy powder containing 3.0 to 6.0% by mass of V.

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