Method for manufacturing a titanium alloy sintered body and titanium alloy sintered body

Abstract

To provide a titanium alloy sintered body with enhanced fatigue strength while reducing an oxygen content, and also to provide a manufacturing method of the titanium alloy sintered body.SOLUTION: A manufacturing method of a titanium alloy sintered body using a metal powder injection molding method includes: a mixing step of preparing a mixture of metal powder and binder; an injection step of injection-molding the mixture to produce a molded body; a defatting step of defatting the molded body to remove the binder; and a sintering step of sintering the molded body with the binder removed to obtain a sintered body. The sintering step is conducted at a sintering temperature of 800 to 995°C and with a sintering time from 6 to 200 hours.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a titanium alloy sintered body and a titanium alloy sintered body, and particularly to a method for manufacturing a titanium alloy sintered body capable of achieving low oxygenation and a titanium alloy sintered body.

Background Art

[0002] Conventionally, titanium is a metal element in the earth's crust, which is the fourth most abundant element after aluminum, iron, and magnesium. It is known to be a metal with low weight, high strength, excellent corrosion resistance, and little adverse effect on the human body. However, titanium has a close-packed hexagonal structure at room temperature, making it difficult to process with deformation. Also, due to its high strength, machining is not easy, resulting in a problem that it is difficult to suppress the manufacturing cost.

[0003] Therefore, in order to suppress the manufacturing cost, there is an increasing expectation for the production of titanium by metal powder injection molding (MIM), which can achieve near-net shape only by product molding without machining.

[0004] For the manufacturing method of a titanium alloy sintered body and the titanium alloy sintered body by such metal powder injection molding, various methods and forms are known. For example, as described in Patent Document 1, a green body is formed using metal powder composed of titanium or a titanium alloy, and in the manufacturing method of a member by powder metallurgy using titanium or a titanium alloy in which the green body is compressed and solidified in the sintering stage, for the formation of the green body, metal powder composed of titanium or a titanium alloy with an average particle size measured using laser light scattering conforming to ASTM standard B822-10 of less than 25 μm is used, and the sintering stage is carried out at a sintering temperature up to 1100 °C, with a sintering time of 5 hours or less, in an atmosphere of reduced pressure with respect to normal pressure. A manufacturing method of a titanium alloy sintered body is known.

[0005] According to this method for manufacturing titanium alloy sintered bodies, titanium or titanium alloys with an average particle size of less than 25 μm in the metal powder used for green body production are used, and the sintering stage is carried out at a sintering temperature of up to 1100°C for a sintering time of 5 hours or less, in an environment with a reduced pressure compared to atmospheric pressure. This process can then be used to selectively influence the particle structure and material properties of the resulting material.

[0006] Furthermore, as described in Patent Document 2, a titanium alloy sintered body is known characterized by having an average crystal grain size on the surface greater than 30 μm and less than or equal to 500 μm, and a Vickers hardness on the surface of 300 or more and less than or equal to 800.

[0007] Such a titanium alloy sintered body prevents surface degradation even when exposed to harsh environments for extended periods, resulting in a titanium alloy sintered body with high mirror-like (aesthetic) properties. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Special Publication No. 2019-516021 [Patent Document 2] Japanese Patent Publication No. 2019-44225 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, it is known that the tensile strength and elongation properties of titanium alloy sintered bodies change depending on the oxygen content; increasing the oxygen content increases tensile strength and decreases elongation. In contrast, it is difficult to keep the oxygen content below 0.2 mass% in titanium alloy sintered bodies produced by conventional manufacturing methods, which presents a problem in increasing fatigue strength.

[0010] This invention has been made in view of the above circumstances, and aims to provide a method for manufacturing a titanium alloy sintered body with reduced oxygen content and increased fatigue strength, and a titanium alloy sintered body. [Means for solving the problem]

[0011] The present invention relates to a method for manufacturing a titanium alloy sintered body by metal powder injection molding, comprising: a kneading step of manufacturing a mixture of metal powder and a binder; an injection step of manufacturing a molded body by injection molding the mixture; a degreasing step of degreasing the molded body to remove the binder; and a sintering step of sintering the molded body from which the binder has been removed to obtain a sintered body, wherein the sintering step has a sintering temperature of 800 to 995°C and a sintering time 48 It is characterized by being carried out over a period of 200 hours. Furthermore, in the method for producing a titanium alloy sintered body according to the present invention, it is preferable that the relative density of the sintered body be 97.5% or higher. Furthermore, in the method for producing a titanium alloy sintered body according to the present invention, it is preferable to have an oxygen content of 0.2% or less in the sintered body.

[0012] Furthermore, in the method for manufacturing a titanium alloy sintered body according to the present invention, the sintering step is carried out under vacuum, and the vacuum is defined as having an atmospheric pressure of 1 × 10⁻⁶ during sintering. -3 It is preferable that the value be Pa or less.

[0013] Furthermore, in the method for producing a titanium alloy sintered body according to the present invention, it is preferable to use low-oxygen metal powder as the metal powder.

[0014] Furthermore, the titanium alloy sintered body according to the present invention is characterized in that, by mass%, it consists of 5.50 to 6.50% aluminum, 3.50 to 4.50% vanadium, 0.40% or less iron, 0.2% or less oxygen, 0.08% or less carbon, 0.05% or less nitrogen, and 0.015% or less hydrogen, with the remainder being titanium, and has a relative density of 97.0% or more.

[0015] Furthermore, in the titanium alloy sintered body according to the present invention, it is preferable that the average grain size is 5.0 to 50.0 μm and the acicular ratio of the crystal structure is 3 or less. [Effects of the Invention]

[0016] According to the method for manufacturing a titanium alloy sintered body according to the present invention, in the sintering process, since the sintering temperature is 980 ° C and the sintering time is 48 hours, a low-oxygen titanium alloy sintered body can be obtained. Further, since the titanium alloy sintered body according to the present invention has a relative density of 97.0% or more and an oxygen content of 0.2 mass% or less, it is possible to provide a titanium alloy sintered body having high fatigue strength.

Brief Description of Drawings

[0017] [Figure 1] Flow chart of the method for manufacturing a titanium alloy sintered body according to an embodiment of the present invention. [Figure 2] Observation results of the microstructure, where (A) is the titanium alloy sintered body according to the present embodiment, and (B) is the observation result of the comparative example. [Figure 3] Graph showing the relationship between the sintering time and relative density of the titanium alloy sintered body according to the present embodiment and the comparative example. [Figure 4] Graph showing the tensile strength test results of the titanium alloy sintered body according to the embodiment of the present invention and the comparative example.

Modes for Carrying Out the Invention

[0018] Hereinafter, preferred embodiments for carrying out the present invention will be described with reference to the drawings. Note that the following embodiments do not limit the invention according to each claim, and not all combinations of the features described in the embodiments are essential for the solution means of the invention.

[0019] FIG. 1 is a flow chart of the method for manufacturing a titanium alloy sintered body according to an embodiment of the present invention, FIG. 2 is an observation result of the microstructure, where (A) is the titanium alloy sintered body according to the present embodiment, and (B) is the observation result of the comparative example, FIG. 3 is a graph showing the relationship between the sintering time and relative density of the titanium alloy sintered body according to the present embodiment and the comparative example, and FIG. 4 is a graph showing the tensile strength test results of the titanium alloy sintered body according to the embodiment of the present invention and the comparative example.

[0020] As shown in Figure 1, the method for manufacturing a titanium alloy sintered body according to this embodiment comprises the steps of: manufacturing a mixture of metal powder and a binder (S101); manufacturing a molded body by injection molding the mixture (S102); degreasing the molded body to remove the binder (S103); sintering the molded body from which the binder has been removed to obtain a titanium alloy sintered body (S104); and performing post-processing and inspection of the titanium alloy sintered body (S105).

[0021] The process for producing a mixture of metal powder and binder (S101) involves mixing the metal powder and binder to produce the mixture. The metal powder preferably consists of conventionally known pure titanium or titanium alloys, and more preferably low-oxygen powder with an oxygen content of 0.13% by mass or less. For example, But, Ti-6 Al -4 V Regarding the material, it is ASTM grade 23 (Extra-Low It is preferable that the powder be equivalent to an interstitial powder.

[0022] The binder is an additive that provides the fluidity necessary for injection molding, as described later. A binder made from a general-purpose synthetic resin with added lubricants and plasticizers is preferably used. The ratio of metal powder to binder can be adjusted as appropriate depending on the properties and shape of the titanium alloy sintered body being manufactured; however, a ratio of 60 vol% to 40 vol% is preferred.

[0023] The compound is manufactured by adding a binder to metal powder, heating and pressurizing the mixture, then cooling and solidifying the mixture, which is then crushed and granulated to obtain a fluid compound.

[0024] The process of manufacturing a molded body by injection molding of a compound (S102) involves injecting the compound into a mold, followed by cooling and solidifying to produce a molded body of a predetermined shape. The mold used for injection molding can be a conventional mold corresponding to the shape of the molded body.

[0025] The step of degreasing the molded body to remove the binder (S103) is a step of removing the binder contained in the molded body to obtain a degreased body prior to sintering, which will be described later. This can be done by a heat degreasing treatment in which the molded body is heated under an inert gas flow to evaporate and thermally decompose the binder, or by a solvent degreasing treatment in which the binder is extracted with an organic solvent.

[0026] The process (S104) of sintering the molded body from which the binder has been removed to obtain a titanium alloy sintered body involves degreasing the body to 1 × 10 -3 The material is sintered by heating it to 800 to 995°C, more preferably to about 980°C, under a vacuum of Pa or less for 6 to 200 hours, more preferably 48 hours. Any remaining binder contained in the degreased material is removed during the heating process by sintering. As the binder is removed from the molded body through degreasing and sintering in this way, the sintered body shrinks by about 10 to 20% compared to the molded body.

[0027] Furthermore, in the process of obtaining a titanium alloy sintered body (S104), a zirconia setter is placed inside a molybdenum container, the degreased material is placed on the setter, the container is closed with a molybdenum lid, and then the container is evacuated to carry out sintering.

[0028] The post-processing and inspection step (S105) of the titanium alloy sintered body is a process in which the titanium alloy sintered body obtained by sintering is subjected to post-processing and inspection. Specifically, this involves heat treatment of the titanium alloy sintered body and polishing to ensure dimensional accuracy. [Examples]

[0029] Next, the present invention will be described in more detail with reference to examples.

[0030] The method for manufacturing a titanium alloy sintered body involved a step (S101) to prepare a mixture of metal powder and a binder. The titanium alloy powder used consisted of 6.22% aluminum, 4.04% vanadium, 0.2% iron, 0.091% oxygen, 0.004% carbon, 0.012% nitrogen, 0.002% hydrogen, with the remainder being titanium, and had an average particle size of 27.3 μm. The binder used was the one described in Japanese Patent No. 5163596, which was mixed and kneaded with the titanium alloy powder at a ratio of 40% by volume. Subsequently, the mixture was injection molded to produce a molded body (S102), and the molded body was degreased to remove the binder (S103), both of which were carried out by heat degreasing.

[0031] The process (S104) of sintering the molded body from which the binder has been removed to obtain a titanium alloy sintered body involves degreasing the body to 1 × 10 -3 Under a vacuum of less than Pa, the temperature was increased and the material was heated to 980°C for 48 hours to sinter it. Because the binder was removed from the molded body through degreasing and sintering, the sintered body shrank by approximately 15% compared to the original molded body. Furthermore, the relative density of the titanium alloy sintered body was 97.5%.

[0032] Furthermore, in the process of obtaining a titanium alloy sintered body (S104), a zirconia setter was placed inside a molybdenum container, the degreased material was placed on the setter, the container was sealed with a molybdenum lid, and then the container was sintered under vacuum.

[0033] In the post-processing and inspection step (S105) of the titanium alloy sintered body, the titanium alloy sintered body obtained by sintering was cut and polished to form a fatigue test specimen. The tensile test specimen was only inspected and no post-processing was performed.

[0034] First, particle size observation tests were conducted on the examples and comparative examples of titanium alloy sintered bodies according to this embodiment. Here, the comparative example was a sintered body prepared using a mixture of ordinary metal powders with a higher oxygen content than the low-oxygen powder used in the titanium alloy sintered body according to this embodiment, and sintered at a temperature of 1100°C for 6 hours. For the particle size observation test, photographs of the surface of the examples and comparative examples were taken at 400x magnification, printed, the outline of the granular structure was traced by hand, and the images were imported into a computer. Then, the equivalent circle diameter, absolute maximum length, diagonal width, and needle-like aspect ratio were measured using measurement software (Winroof). Furthermore, particles with an equivalent circle diameter of less than 5 μm were excluded from the measurement data, and the average equivalent circle diameter, average absolute maximum length, average diagonal width, and average needle-like aspect ratio were calculated. The mean circle equivalent diameter is the diameter of an equivalent circle with the same area as the object; the absolute maximum length is the length of the longest part of the object; the diagonal width is the shortest distance between two lines parallel to the maximum absolute length when the object is placed between them; and the needle-shape ratio is the absolute maximum length divided by the diagonal width.

[0035] As shown in Figure 2, the titanium alloy sintered body obtained by the manufacturing method of the titanium alloy sintered body according to this embodiment exhibits a microstructure with a generally rounder grain size compared to the conventional comparative example. As shown in Figure 2(A), it can be confirmed that the needle-like aspect ratio of the crystalline structure in the microfibers of the titanium alloy sintered body according to this embodiment is 3.0 or less. In contrast, as shown in Figure 2(B), the conventional comparative example has a generally elongated crystalline structure with a needle-like aspect ratio of 3.0 or more, confirming that the titanium alloy sintered body according to this embodiment has a generally finer and rounder crystalline structure compared to the comparative example.

[0036] The particle size observation results for the examples are as follows. [Table 1]

[0037] Next, as shown in Figure 3, it was confirmed that the relative density of the titanium alloy sintered body using low-oxygen powder could be obtained at a relative density of 98% or higher, equivalent to that of the comparative example, by sintering for 48 hours.

[0038] Furthermore, as shown in the table below, the results of the oxygen, nitrogen, and carbon analysis of the titanium alloy sintered body according to this embodiment were found to have nitrogen and carbon content equivalent to that of the comparative example, and an oxygen content of 0.18%, which was significantly lower than that of the comparative example. This satisfies the conditions of JIS standard 60 and ASTM standard Gr5 for molten materials. [Table 2]

[0039] Next, tensile strength tests and fatigue strength tests were performed on the titanium alloy sintered body according to this embodiment and the comparative example. For the tensile strength test, the scoring distance was set to 15 mm. As shown in Figure 4, the tensile strength of the embodiment was equivalent to that of the comparative example, and it was confirmed that the elongation of the embodiment was higher than that of the comparative example.

[0040] The fatigue strength test was conducted under the following conditions. (1) Test temperature: Room temperature (2) Standard: ASTM E466 (3) Stress ratio: R = 0.1 (4) Waveform: Sine wave (5) Termination cycle: 1.0 × 10 7 cycle (6) Frequency: 10Hz

[0041] The fatigue strength test result was 1.0 × 10⁻⁶ 7 The fatigue strength during the cycle was 350 MPa in the example and 280 MPa in the comparative example.

[0042] Thus, it has been confirmed that the method for manufacturing a titanium alloy sintered body according to this embodiment makes it possible to obtain a titanium alloy sintered body with reduced oxygen content and increased fatigue strength.

Claims

1. A kneading process for producing a mixture of metal powder and binder, An injection molding process to manufacture a molded body by injection molding the aforementioned kneaded material, A degreasing step of degreasing the molded body and removing the binder, A method for manufacturing a titanium alloy sintered body by metal powder injection molding, comprising a sintering step of sintering the molded body from which the binder has been removed to obtain a sintered body, The method for manufacturing a titanium alloy sintered body is characterized in that the sintering step is performed at a sintering temperature of 800 to 995°C and for a sintering time of 48 to 200 hours.

2. In the method for manufacturing a titanium alloy sintered body according to Claim 1, A method for manufacturing a titanium alloy sintered body, characterized in that the relative density of the sintered body is 97.5% or more.

3. In the method for manufacturing a titanium alloy sintered body according to Claim 1, A method for manufacturing a titanium alloy sintered body, characterized in that the oxygen content of the sintered body is 0.2% or less.

4. In the method for manufacturing a titanium alloy sintered body according to claim 1, The sintering process is carried out under vacuum. The vacuum is defined as having an atmospheric pressure of 1 × 10⁻⁶ during sintering. －３ A method for manufacturing a titanium alloy sintered body, characterized by having a hardness of Pa or less.

5. In the method for manufacturing a titanium alloy sintered body according to claim 1 or 2, The method for manufacturing a titanium alloy sintered body is characterized by using low-oxygen metal powder as the metal powder.

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