Method for manufacturing titanium sintered material

Abstract

To provide a manufacturing method of a titanium sintered material capable of reducing manufacturing cost.SOLUTION: A manufacturing method of a titanium sintered material includes the steps of: preparing titanium-based starting material powder prepared so that a hydrogen content is 0.2 to 2.0 mass% based on the entire powder; filling the titanium-based starting material powder into a non-sealed mold; and heating and sintering the titanium-based starting material powder in the mold without applying a pressure to obtain a titanium sintered material.SELECTED DRAWING: None

Description

Technical Field

[0001] This invention relates to a method for manufacturing a titanium sintered material by which a titanium sintered material is obtained by powder metallurgy.

Background Art

[0002] Titanium is a lightweight material having a specific gravity about half that of steel and has excellent corrosion resistance and strength. Therefore, it is used for parts of aircraft, railway vehicles, motorcycles, automobiles, etc. with strong lightweight needs, as well as for home appliances and building members. Further, from the viewpoint of excellent corrosion resistance, it is also used as a medical material.

[0003] Titanium materials are manufactured by powder metallurgy using titanium powder as a starting material, as described in, for example, Japanese Patent Application Laid-Open No. 2017-88908 (Patent Document 1). The method for manufacturing a titanium sintered material disclosed in this Patent Document 1 includes the following steps. a) A step of mixing titanium component powder and nitride particles of a metal other than titanium. b) A step of applying a compressive force to the mixed powder to form it and produce a compression solidified body. c) A step of heat-sintering the compression molded body obtained by compression molding in a vacuum atmosphere containing no oxygen.

[0004] Titanium powder (pure titanium powder or titanium alloy powder) as a starting material is more expensive than iron-based materials and aluminum-based materials.

[0005] Japanese Patent No. 3459342 (Patent Document 2) describes a method of hydrogenating titanium or a titanium alloy by utilizing the hydrogen embrittlement of titanium or a titanium alloy, followed by pulverizing it to an arbitrary particle size to obtain hydrogenated titanium powder, and dehydrogenating this by vacuum heating to convert it to titanium powder, i.e., a hydrogenation-dehydrogenation method.

[0006] Hydrogenated titanium (TiH while being hydrogenated 2High-concentration hydrogen-containing titanium powder containing a compound (hereinafter referred to as "high-hydrogen titanium powder" or "hydrogenated titanium powder") has a lower market price compared to dehydrogenated titanium powder. Hydrogenated fine titanium powder with a particle size of 10 μm or less has a large specific surface area and takes in a large amount of oxygen in the air due to the processing heat during pulverization. Therefore, hydrogenated titanium powder with a particle size of 10 μm or less is usually not used as an alloy raw material.

[0007] Japanese Patent Application Laid-Open No. 2020-63509 (Patent Document 3) proposes a method for providing a titanium sintered material with high strength and high toughness while reducing production costs by actively utilizing hydrogenated titanium powder with a particle size of 10 μm or less that is usually discarded. Specifically, the method for manufacturing a titanium sintered material disclosed in Patent Document 3 includes the following steps. d) A step of mixing fine hydrogenated titanium powder and titanium powder with a larger particle size. e) A step of compression molding the mixed powder to obtain a compression solid. f) A step of subjecting the compression solid to a dehydrogenation treatment and then sintering it under vacuum.

[0008] The methods for manufacturing titanium sintered materials described in Patent Document 1, Patent Document 3, etc. are to pressure-mold the mixed powder of starting materials with a press to produce a compression solid, and then sinter the compression solid under vacuum. As a method for manufacturing a titanium sintered material different from the above method, there is also a method of consolidating titanium powder or mixed powder by hot isostatic pressing (HIP) or cold isostatic pressing (CIP), and sintering the consolidated body under vacuum.

[0009] The paper "Powder metallurgy of titanium - past, present and future" by Zhigang Zak Fang et al. (INTERNATIONAL MATERIALS REVIEW, 2017) (Non - Patent Document 1) describes the advantages of using titanium hydride powder. Specifically, it is described that during the press - forming process, brittle titanium hydride powder is crushed into fine particles, and these particles fill the gaps between titanium powders, thereby improving the density of the compact. Also, it is described that hydrogen in the titanium powder diffuses rapidly, enhancing the sinterability.

[0010] In the method for manufacturing a titanium sintered material described in Non - Patent Document 1, a mixed powder containing titanium hydride powder is also made into a compression - solidified body by a hot isostatic pressing method (HIP) or a cold isostatic pressing method (CIP), and this compression - solidified body is sintered under vacuum.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Patent Document 3

Non - Patent Documents

[0012]

Non - Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0013] What is common to conventional methods for manufacturing titanium sintered materials is that raw material powder is compressed to produce a compression solidified body, and the compression solidified body is heated and sintered in a vacuum atmosphere. Compressing the raw material powder is to reduce the pores existing between the powders, increase the contact area between the powders, and improve the sinterability. Also, sintering in a vacuum atmosphere is to prevent oxygen from being incorporated into the sintered body.

[0014] The problems with the conventional manufacturing methods are that in order to produce a compression solidified body of titanium powder or raw material powder, a press machine, HIP equipment, CIP equipment, etc. are required, increasing the equipment cost. Also, batch-type vacuum sintering equipment for suppressing oxygen contamination is needed, reducing productivity and ultimately increasing the manufacturing cost.

[0015] An object of the present invention is to provide a method for manufacturing a titanium sintered material capable of reducing the manufacturing cost.

Means for Solving the Problems

[0016] The method for manufacturing a titanium sintered material according to the present invention includes the following steps. a) A step of preparing a titanium-based starting material powder adjusted so that the hydrogen content with respect to the whole powder is 0.2 to 2.0 mass%. b) A step of filling the titanium-based starting material powder into a non-sealed type mold. c) A step of obtaining a titanium sintered material by heating and sintering the titanium-based starting material powder in the mold without applying pressure.

[0017] The titanium-based starting material powder may be a single type of powder or a mixed powder of a plurality of types of powders. Also, the terms "titanium-based" and "titanium" as used in this specification are terms that include both pure titanium consisting essentially of only titanium as a metal element and titanium alloys containing titanium as the main component of the metal element.

[0018] In a preferred embodiment, the titanium-based starting material powder is a mixed powder of a high-hydrogen titanium powder intentionally containing hydrogen and a low-hydrogen titanium powder unavoidably containing hydrogen.

[0019] In the above preferred embodiment, the high-hydrogen titanium powder is a high-concentration hydrogen-containing titanium powder (hydrogenated titanium powder) containing a hydrogenated titanium (TiH 2 ) compound in the hydrogenated state, and the low-hydrogen titanium powder is a titanium powder that has not been hydrogenated or has been dehydrogenated after hydrogenation treatment. An example of the low-hydrogen titanium powder that has not been hydrogenated is atomized powder.

[0020] The hydrogen content in the hydrogenated titanium powder is generally 2.0 to 4.0% by mass, and the hydrogen content in the low-hydrogen titanium powder that inevitably contains hydrogen is generally 0.01 to 0.08% by mass. In this case, preferably, the amount of the high-hydrogen titanium powder with respect to the entire mixed powder is 10 to 55% by mass.

[0021] In another embodiment, the hydrogen content in the hydrogenated titanium powder is adjusted to be 0.8 to 1.5% by mass. The hydrogen content in the low-hydrogen titanium powder is 0.01 to 0.08% by mass. In this case, preferably, the amount of the high-hydrogen titanium powder with respect to the entire mixed powder is 20% by mass or more and less than 100% by mass.

[0022] In still another embodiment, the titanium-based starting material powder consists only of a high-hydrogen titanium powder prepared so that the hydrogen content is intentionally 0.8 to 1.5% by mass.

[0023] In some embodiments described herein, the titanium-based starting material powder consists of pure titanium substantially containing only titanium as a metal element. In this case, if the titanium-based starting material powder is a mixed powder of a high-hydrogen titanium powder and a low-hydrogen titanium powder, both the high-hydrogen titanium powder and the low-hydrogen titanium powder consist of pure titanium.

[0024] In other embodiments described herein, at least one of the high-hydrogen titanium powder and the low-hydrogen titanium powder consists of a titanium alloy containing titanium as a main component. Both the high-hydrogen titanium powder and the low-hydrogen titanium powder may consist of a titanium alloy.

[0025] The heat sintering carried out without applying pressure to the titanium-based starting material powder in the mold utilizes the rapid diffusion of hydrogen decomposed from TiH contained in a large amount in the starting material powder. Therefore, even if a compression solid is not produced before sintering, solid-phase sintering at the interface of adjacent powder particles proceeds well, and the sinterability is improved. 2 Since it is carried out by utilizing the rapid diffusion of hydrogen decomposed from TiH contained in a large amount in the starting material powder, solid-phase sintering at the interface of adjacent powder particles proceeds well without producing a compression solid before sintering, and the sinterability is improved.

[0026] The heat sintering of the titanium-based starting material powder in the mold may be carried out in a vacuum atmosphere or in a non-vacuum atmosphere. Since the shielding effect of hydrogen gas generated from the inside of the starting material powder suppresses the mixing of oxygen into the titanium material, good sintering can be carried out even in a non-vacuum atmosphere.

[0027] The heat sintering of the titanium-based starting material powder in the mold includes, for example, the following. d) Heating from room temperature to an intermediate temperature range where hydrogen in the starting material powder is dissociated from titanium. e) Holding the titanium-based starting material powder in the above intermediate temperature range to dissociate hydrogen from titanium, and promoting sintering between powders by utilizing the rapid diffusibility of the dissociated hydrogen. f) Heating the titanium-based starting material powder from the intermediate temperature range to a high temperature range where sintering of the titanium-based starting material powder is carried out. g) Holding the titanium-based starting material powder in the high temperature range to complete sintering. h) Cooling the sintered body after sintering completion from the high temperature range to room temperature.

[0028] The above intermediate temperature range is preferably in the range of 550°C to 850°C. Also, the high temperature range is in the range of 850 to 1400°C. In one embodiment, the intermediate temperature range has a low-temperature side intermediate temperature range and a high-temperature side intermediate temperature range, and the titanium-based starting material powder is heated to the high-temperature side intermediate temperature range after being held in the low-temperature side intermediate temperature range, and then heated to the above high temperature range after being held in the high-temperature side intermediate temperature range.

[0029] When the titanium-based starting material powder is a mixed powder of high-hydrogen titanium powder and low-hydrogen titanium powder, the low-hydrogen titanium powder is typically dehydrogenated titanium powder or atomized powder.

[0030] In one embodiment, the high-hydrogen titanium powder and the low-hydrogen titanium powder are made of pure titanium containing substantially only titanium as a metal element. In the case of this embodiment, a trace amount of iron (Fe) powder may be further added to the above mixed powder.

[0031] In other embodiments, at least one of the high-hydrogen titanium powder and the low-hydrogen titanium powder is made of a titanium alloy containing titanium as a main component. As the titanium alloy, for example, a 64 titanium alloy (Ti-6Al-4V) is applied.

Advantages of the Invention

[0032] According to the present invention, if a titanium-based starting material powder prepared so that the hydrogen content with respect to the whole powder is 0.2 to 2.0% by mass is put into a non-sealed type mold and heat-sintered in the mold without applying pressure, the solid-phase sinterability between powder particles is enhanced by utilizing the high-speed diffusion of decomposed hydrogen. Thus, conventional presses, CIP equipment, and HIP equipment are not required, and the equipment cost can be significantly reduced.

Brief Description of the Drawings

[0033]

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Figure 11

Mode for Carrying Out the Invention

[0034] The inventors of the present application considered that when hydrogen is excessively contained in titanium powder, a dense solid-phase sintered compact might be obtained by utilizing the high-speed diffusibility of hydrogen, and conducted various experiments. Although the data will be shown and explained in detail later, as a conclusion, if the hydrogen content in the titanium powder as a starting material is adjusted to an appropriate range, the powder is put into a non-sealed type mold and heated and sintered under appropriate conditions, the hydrogen generated by the decomposition of TiH 2 diffuses rapidly between titanium powder particles, and accordingly, the titanium component also diffuses between powder particles to promote solid-phase sintering. At that time, it was also found that a dense sintered material can be obtained without applying pressure to the titanium-based starting material powder in the mold. It was also found that sintering in a non-vacuum atmosphere is possible because the shielding effect of hydrogen gas generated from the inside of the titanium powder during the heat treatment suppresses the mixing of oxygen into the titanium material. As a result, since a continuous non-vacuum sintering facility can be used instead of the conventional batch-type vacuum sintering facility, there is an economic advantage that the cost related to the sintering process can be reduced.

[0035] The following points can be cited as important factors for obtaining a titanium sintered material by utilizing the high-speed diffusion of hydrogen.

[0036] a) Use of a non-sealed type mold

[0037] b) Utilization of high-hydrogen titanium powder

[0038] c) Mixing ratio of high-hydrogen titanium powder and low-hydrogen titanium powder

[0039] d) Gentle heating rate to suppress rapid hydrogen release from titanium powder

[0040] e) Holding at an intermediate temperature to fully decompose TiH 2

[0041] f) Holding at a high temperature for sufficient sintering

[0042] [Verification basic experiment of powder filling sintering method using a small mold]

[0043] [Verification 1: Use of an upper-open alumina mold]

[0044] A titanium-based starting material powder consisting only of high-hydrogen titanium powder in the as-hydrogenated state was filled into an upper-open alumina mold with longitudinal and transverse dimensions of 120 mm × 120 mm, heated from room temperature to 1000 °C in a vacuum atmosphere without applying pressure, held at 1000 °C for 24 hours for sintering, and then cooled in the furnace.

[0045] The hydrogen content in the commercially available high-hydrogen titanium powder in the as-hydrogenated state is generally 2.0 - 4.0 mass%.

[0046] For comparison, a titanium-based starting material powder consisting only of low-hydrogen titanium powder that had been dehydrogenated after hydrogenation treatment was also prepared, and the starting material powder consisting only of low-hydrogen titanium powder was sintered under the same conditions as the heating and sintering conditions of the starting material powder consisting only of the above high-hydrogen titanium powder. The hydrogen content in the commercially available low-hydrogen titanium powder is generally 0.01 - 0.08 mass%.

[0047] ​As a result, the alumina mold filled with the starting material powder consisting only of high-hydrogen titanium powder was damaged. On the other hand, the alumina mold filled with the starting material powder consisting only of low-hydrogen titanium powder was not damaged. The reason is thought to be that when using the starting material powder consisting only of high-hydrogen titanium powder, during the heating process and the sintering process, the sintering progress body expanded due to the decomposition of TiH 2 and the release of hydrogen, destroying the alumina mold.

[0048] From the above verification, in order to avoid the rapid volume expansion of the sintering progress body, it is desirable to prepare the hydrogen content in the titanium-based starting material powder within an appropriate range. When the hydrogen content in the high-hydrogen titanium powder is 2.0% or more, it is not desirable to set the ratio of the high-hydrogen titanium powder to 100%, but it is desirable to use a starting material powder obtained by mixing the high-hydrogen titanium powder and the low-hydrogen titanium powder. To suppress the rapid decomposition of TiH 2 and the rapid release of hydrogen, it is desirable to avoid rapid temperature rise and heating. It has been found that it is desirable to use a high-strength mold (for example, made of stainless steel) that can withstand the volume expansion of the sintering progress body.

[0049] [Verification 2: Sintering acceleration by high-speed diffusion of hydrogen]

[0050] As starting materials, pure titanium powder and hydrogenated pure titanium powder after hydrogenation treatment were prepared, and the amount of hydrogenated pure titanium powder in the total mixed powder was adjusted to be 30% by mass. The pure titanium powder was pure titanium powder that had been dehydrogenated after hydrogenation treatment, and the hydrogen content in the powder was in the range of 0.01 to 0.08% by mass. The hydrogen content in the hydrogenated pure titanium powder after hydrogenation treatment was in the range of 2.0 to 4.0% by mass.

[0051] As a small mold, a metal mold (50 mm × 70 mm × 10 mmH) with an open top was prepared.

[0052] The mixed powder was filled into a small mold, heated from room temperature to an intermediate temperature of 600 °C in a vacuum atmosphere without applying pressure, held at 600 °C for about 1.5 hours, then heated to a high temperature of 1000 °C, held at 1000 °C for about 2 hours, and then cooled in the furnace. The holding at 600 °C for about 1.5 hours at the intermediate temperature was to fully decompose TiH 2 in this temperature range and effectively utilize the high-speed diffusibility of the dissociated hydrogen.

[0053] The hydrogen content in the raw material powder (mixed powder) was 1.105% by mass, the oxygen content was 0.457% by mass, and the nitrogen content was 0.109% by mass. The hydrogen content of the sintered material after sintering was 0.009% by mass, the oxygen content was 0.409% by mass, and the nitrogen content was 0.028% by mass.

[0054] Figure 1 is a photograph showing the raw material powder before sintering filled in the mold and the sintered material after sintering. The amount of hydrogenated pure titanium powder with respect to the entire raw material powder before sintering was 30% by mass, and the hydrogen content in the entire raw material powder was 1.105% by mass.

[0055] There was a gap between the sintered material after sintering and the inner surface of the mold, and it was confirmed that the raw material powder shrank during the sintering process to become the sintered material. The shrinkage rate was 14.3%. Also, the weight per 1 cm 3 of the sintered material was 3.85 g, and the relative density was 86.5%.

[0056] Figure 2 is a photograph showing the upper surface part, the central part, and the bottom surface part of the longitudinal section of the sintered material after sintering. No pores were observed in the central part, and it was confirmed that the density was high. This can be considered because the hydrogen generated by the decomposition of TiH 2 diffused rapidly between the powder particles, promoting the solid-phase sintering between the titanium particles.

[0057] In the upper surface part and the bottom surface part, many pores were observed, which are considered to be formed when the hydrogen gas escapes to the outside. If the heating rate during the sintering process is too high, the amount of hydrogen escaping from the raw material powder increases, which may hinder the sintering that utilizes the high-speed diffusion of hydrogen.

[0058] [Verification 3: Heating Rate]

[0059] Figure 3 is a photograph showing two sintered materials sintered at different heating rates. The starting materials were both mixtures of low-hydrogen pure titanium powder and as-hydrogenated high-hydrogen pure titanium powder, and the amount of high-hydrogen pure titanium powder relative to the total mixed powder was adjusted to 30% by mass. The hydrogen content of the total mixed powder was 0.8% by mass. Photograph (a) is a titanium sintered material prepared at a heating rate of 50 °C / min during the heat sintering process, and photograph (b) is a titanium sintered material prepared at a heating rate of 20 °C / min. As is clear from comparing the two photographs, it is recognized that the higher the heating rate, the easier cracks occur.

[0060] [Verification 4: Strength Characteristics of Sintered Materials Obtained by Powder Filling Sintering Method Using a Mold]

[0061] Low-hydrogen pure titanium powder and high-hydrogen pure titanium powder were mixed, and the amount of high-hydrogen pure titanium powder relative to the total mixed powder was adjusted to 40% by mass to obtain starting materials. The starting material powder was filled into a mold, heated from room temperature to 600 °C at a heating rate of 10 - 20 °C / min in a vacuum atmosphere without applying pressure, held at 600 °C for 1.5 hours, then heated to 1000 °C at a heating rate of 10 - 20 °C / min, held at 1000 °C for 2 hours for sintering, and then cooled in the furnace to obtain a sintered material. The hydrogen content of the total starting material powder was 1.13% by mass.

[0062] Figure 4 is a photograph of the sintered material sintered under the above conditions. As is clear from the photograph, the sintered material had no internal cracks, and its relative density was 89.5%.

[0063] The sintered material obtained as described above was subjected to hot plastic working to produce a prototype material for the strength test. Table 1 shows a comparison of the characteristics between the prototype material and four types of JIS pure titanium.

[0064]

Table 1

[0065] As can be seen from Table 1, it is recognized that the prototype material is superior to JIS Grade 4 pure titanium in terms of each property of tensile strength, tensile strength, and elongation at break.

[0066] [Verification 5: Structure of the Mold]

[0067] It was confirmed that as the mold for filling the starting raw material powder, any non-sealed type can be used, and a mold having the structure schematically shown in FIG. 5 can be used.

[0068] In FIG. 5, what is shown in (a) is an upper-open type mold, (b) is a structure in which a lid is placed on the raw material powder filled in the upper-open mold. There is a gap between the lid and the inner wall surface of the mold. (c) is a structure in which a lid is placed on the upper end surface of the side wall of the upper-open mold, and there is a minute gap between the lid and the upper end surface of the side wall of the mold. The merit of using the lid is to prevent the powder in the mold from flying.

[0069] The mold structures shown in FIGS. 5(a), 5(b), and 5(c) are exemplary, and any non-sealed type mold other than the structures shown in FIG. 5 can also be used.

[0070] [Verification 6: Influence of Particle Size of Titanium Hydride Powder]

[0071] As starting raw materials, pure titanium powder and titanium hydride powder were prepared, and the amount of titanium hydride powder in the total mixed powder was adjusted to 50% by mass. As the titanium hydride powder to be used, those having an average particle size of less than 10 μm, those having an average particle size of 10 to less than 45 μm, and those having an average particle size of 45 to less than 150 μm were prepared.

[0072] The starting material mixed powder was filled into an open-top mold (91 mm × 91 mm), and without applying pressure in a vacuum atmosphere, the temperature was raised from room temperature to 600 °C (heating rate 10 - 20 °C / min), held at 600 °C for 2 hours, then the temperature was raised to 1000 °C at a heating rate of 10 - 20 °C / min, held at 1000 °C for 24 hours for sintering, and then cooled in the furnace.

[0073] Figure 6 shows the micrographs of the sintered materials after sintering. (a) shows the case where titanium hydride powder with an average particle size of less than 10 μm was used, (b) shows the case where titanium hydride powder with an average particle size of 10 - less than 45 μm was used, and (c) shows the case where titanium hydride powder with an average particle size of 45 - less than 150 μm was used. The density of the sintered material in (a) is 99.8%, and the presence of pores is slight. The density of the sintered material in (b) is 96.2%, and it was observed that pores were dispersed. The density of the sintered material in (c) is 82.9%, and it was observed that the area (volume) of the dispersed pores was large.

[0074] From the results shown in Figure 6, it was confirmed that the sintering density is improved when using fine-grained titanium hydride powder.

[0075] [Preferred heating and sintering conditions]

[0076] The preferred features of the titanium powder filling sintering method using a non-sealed type mold are as follows.

[0077] a) Raise the temperature from room temperature to an intermediate temperature range and hold at the intermediate temperature for a certain period of time.

[0078] Holding at the intermediate temperature range for a certain period of time is to decompose TiH 2 sufficiently and utilize the high-speed diffusion of the dissociated hydrogen to promote sintering. The intermediate temperature range for decomposing TiH 2 is 550 °C - 850 °C, and there is no limit to the holding time, but for example, it is about 1 hour - 3 hours.

[0079] b) Raise the temperature from the intermediate temperature range to a high temperature range and hold at the high temperature range for a certain period of time.

[0080] Maintaining at a high temperature zone for a certain period of time is for performing complete sintering. The appropriate sintering temperature varies depending on the alloy composition. For a titanium sintered material mainly composed of titanium, the high temperature zone for performing complete sintering is 850°C to 1400°C, and although there is no limitation on the holding time, it is, for example, about 2 hours to 24 hours.

[0081] c) Heating rate from room temperature to intermediate temperature and from intermediate temperature to high temperature

[0082] TiH 2 In order to suppress the rapid decomposition of TiH and the release of dissociated hydrogen to the outside, it is desirable to set the heating rate in the range of 10°C / min to 30°C / min.

[0083] d) Heating and sintering atmosphere

[0084] From the viewpoint of suppressing the incorporation of oxygen into the titanium material, it is desirable to use a vacuum atmosphere as the heating and sintering atmosphere for obtaining a titanium sintered material. However, in the case of the powder filling sintering method using a non-sealed type mold, even in a non-vacuum atmosphere such as an argon atmosphere, sintering can be performed while suppressing the incorporation of oxygen into the titanium material. The reason is that the shielding effect of hydrogen gas generated from the inside of the titanium material can suppress the mixing of oxygen into the titanium material.

[0085] [High-hydrogen titanium powder]

[0086] High-hydrogen titanium powder is a high-concentration hydrogen-containing titanium powder (hydrogenated titanium powder) containing a hydrogenated titanium (TiH 2 ) compound while being in the hydrogenated state, and contains a large amount of hydrogen. The hydrogen content in the commercially available hydrogenated titanium powder is generally in the range of 2.0 to 4.0% by mass, but it is also possible to intentionally adjust the hydrogen content. In the mold powder filling sintering method of the present invention, if a finer hydrogenated titanium powder is used, an improvement in the density of the sintered material can be expected, but there is no particular need to limit the particle size.

[0087] In this specification, the term "titanium powder" includes not only pure titanium powder but also titanium alloy powders mainly composed of titanium such as 64 titanium alloy (Ti-6Al-4V).

[0088] [Low-hydrogen titanium powder]

[0089] Low-hydrogen titanium powder includes titanium powder that has been dehydrogenated after hydrogenation treatment and titanium powder obtained by the atomization method. In this specification, the term "titanium powder" includes not only pure titanium powder but also titanium alloy powders mainly composed of titanium. The hydrogen content in low-hydrogen titanium powder is an unavoidably contained amount, generally 0.01 to 0.08% by mass.

[0090] [Test on varying the blending ratio of high-hydrogen titanium powder and low-hydrogen titanium powder]

[0091] [Test 1]

[0092] Under the following conditions, the blending ratio of high-hydrogen titanium powder (hydrogen content: 2.0 to 4.0% by mass) and low-hydrogen titanium powder (hydrogen content: 0.01 to 0.08% by mass) was varied, and the density of the obtained sintered body and the properties after rolling (tensile strength and elongation at break) were measured.

[0093] Weight of starting material powder: 500 g

[0094] Inner dimensions of the non-sealed type mold used: 101 mm × 101 mm

[0095] Sintering atmosphere: Vacuum

[0096] Temperature rising and sintering pattern:

[0097] Room temperature → Heating to 600 °C (holding for 1.5 h) → Heating to 800 °C (holding for 1.5 h) → Heating to 1000 °C (holding for 10 h) → Cooling in the furnace → Taking out the mold from the furnace at around 50 °C.

[0098] Hydrogenated titanium powder used: As-hydrogenated pure titanium powder with an average particle size of 10 μm or less

[0099] Low-hydrogen titanium powder used: Dehydrogenated pure titanium powder with an average particle size exceeding 10 μm and 45 μm or less

[0100] Measurement of density: By the Archimedes method corresponding to the "liquid displacement method" described in JIS Z8807

[0101] Calculation of relative density (%): Assuming the specific gravity of pure Ti is 4.51 g / cm 3 and calculating

[0102] The results are shown in Table 2 below.

[0103]

Table 2

[0104] Looking at Samples No. 2 to 4 where the ratio of hydrogenated titanium powder (high-hydrogen titanium powder) to the total mixed powder is 20 to 50 mass%, the hydrogen content in the mixed powder is 0.666 mass% to 1.707 mass%, and the relative density of the sintered body is 94.3 to 96.2%. Also, the tensile strength after rolling of Samples No. 2 to 3 is 702 to 798 MPa, and the elongation at break is 30.0 to 30.3%. These relative density and post-rolling properties are values that can be utilized as practically effective titanium sintered materials. As the relative density of a practically effective titanium sintered material, 85% or more is desirable.

[0105] The hydrogen content in the starting material powder of Sample No. 1 without hydrogenated titanium powder is 0.012 mass%, and the relative density of the sintered body is 88.1%.

[0106] From Samples No. 1 to 4, it is recognized that if the starting material powder contains hydrogenated titanium powder and the hydrogen content in the mixed powder is 0.6 mass% or more, the density of the sintered body will improve.

[0107] Samples Nos. 5 to 6 have a titanium hydride powder content of 60% by mass or more in the mixed powder and a hydrogen content in the mixed powder exceeding 2.0%. Since the sintered compacts of these Samples Nos. 5 to 6 cracked during the sintering process, the relative density was not measured. From this result, it is considered desirable to set the hydrogen content in the mixed powder to 2.0% by mass or less in order to prevent cracking of the sintered compact.

[0108] Also, when the hydrogen content in the high-hydrogen titanium powder is 2.0 to 4.0% by mass and the hydrogen content in the low-hydrogen titanium powder is an inevitable amount (0.01 to 0.08% by mass), it is recognized that it is desirable to set the amount of the high-hydrogen titanium powder with respect to the entire mixed powder to 55% by mass or less. In Test 1, the lower limit of the amount of the high-hydrogen titanium powder with respect to the entire mixed powder was set to 20% by mass (Sample No. 2). The relative density of the sintered compact of Sample No. 2 is 94.3%, which is considerably higher than that of Sample No. 1 that does not contain high-hydrogen titanium powder. From the viewpoint of satisfying the target relative density of 85% or more, it is considered that the amount of the high-hydrogen titanium powder with respect to the entire mixed powder is preferably 10% by mass or more.

[0109] [Test 2]

[0110] Hydrogenated pure titanium powder (average particle size: 48 μm, hydrogen content: 2.0 to 4.0% by mass)) and hydrogenated / dehydrogenated pure Ti powder (average particle size: 28 μm) were used as starting materials, and the two powders were mixed at the blending ratios shown in Table 3 below.

[0111] After filling 100 g of each mixed powder into a rectangular mold (unsealed type mold) with an inner dimension width of 50 mm × length of 70 mm, the mold was put into a vacuum heating furnace and heated and sintered under the following heating and temperature rising pattern.

[0112] Temperature rising and sintering pattern:

[0113] Room temperature → heating to 650°C (holding for 1.5 h) → heating to 800°C (holding for 1.5 h) → heating to 1000°C (holding for 10 h) → furnace cooling → taking out the mold from the furnace at around 50°C.

[0114]

Table 3

[0115] Regarding the mixed powder of Sample No. 105 in Table 3, the results of observation using a scanning electron microscope (SEM) are shown in Fig. 7. Since each starting material powder (titanium hydride powder and hydrogenated / dehydrogenated pure titanium powder) is produced by mechanical pulverization, the powder particles have an angular shape. In Fig. 7, the relatively coarse powder indicated by the arrow is the titanium hydride powder. Although there is a difference in particle size, the two powders are mixed relatively uniformly.

[0116] Analysis and external appearance observation of the density, relative density, oxygen content, nitrogen content, and hydrogen content of the rectangular titanium (Ti) sintered body obtained through the temperature increase / sintering pattern were carried out. The density was measured using the Archimedes method, and the relative density (%) was calculated assuming the specific gravity of pure Ti to be 4.51 g / cm 3 and the results are described in Table 3.

[0117] In Samples No. 102 to 105 (Examples of the present invention) where the ratio of titanium hydride powder to the total mixed powder is 10 to 50% by mass, the relative density is 85% or more, and the external appearance of the sintered body is also good.

[0118] In Sample No. 101 as a comparative example, since it does not contain titanium hydride powder as a starting material, the progress of the sintering phenomenon is insufficient, it does not satisfy the target value of the relative density (85% or more), and the occurrence of a concave portion is confirmed near the center of the sample due to the non-uniform sintering phenomenon.

[0119] In Sample No. 106 as a comparative example, the ratio of titanium hydride powder to the total mixed powder is 60% by mass, and a large amount of hydrogen is generated during the temperature increase / sintering process, so fine cracks occur on the surface of the sintered body.

[0120] Note that, as the blending ratio of titanium hydride powder in the mixed powder increases, that is, as the hydrogen content increases, the amount of oxygen contained in the titanium material after sintering tends to decrease. This is due to the following effect. That is, when the titanium hydride powder thermally decomposes during the sintering process, the hydrogen atoms dissociated and generated react with the oxygen contained in the sample (reduction effect of hydrogen), resulting in a decrease in the oxygen content after sintering.

[0121] Focusing on the residual hydrogen amount after sintering of Samples No. 102 to 106 prepared so that the amount of titanium hydride powder is 10 to 60%, the value is 0.01% by mass or less, satisfying the JIS standard (H ≦ 0.013% by mass).

[0122] For the sintered bodies of Sample No. 101 (comparative example) and Sample No. 104 (example), the microstructure near the center of each sample was observed using an optical microscope. The results are shown in Fig. 8. Fig. 8(a) shows the result of Sample No. 101, and Fig. 8(b) shows the result of Sample No. 104. From Fig. 8, it can be seen that the amount of pores in Sample No. 104 (example) is smaller than that in Sample No. 101 (comparative example), and the density is increasing.

[0123] [Test 3]

[0124] The low-hydrogen titanium powder is not limited to titanium hydride dehydrogenated powder, and for example, titanium powder produced by the atomization method may also be used. An experiment was conducted using gas-atomized pure titanium powder as the starting material. Specifically, it is as follows.

[0125] Using titanium hydride powder (average particle size: 48 μm, hydrogen content: 2.0 to 4.0% by mass) and gas-atomized pure titanium powder (average particle size: 27 μm, hydrogen content: 0.01 to 0.08% by mass) as starting materials, the two powders were mixed at the blending ratios shown in Table 4.

[0126] After filling 100 g of each mixed powder into a non-sealed rectangular mold (mold) with an inner dimension width of 50 mm × length of 70 mm, the mold was placed in a vacuum heating furnace and heated and sintered under the following heating and sintering pattern conditions.

[0127] Heating and sintering pattern:

[0128] Room temperature → Heat up to 650 °C (hold for 1.5 h) → Heat up to 800 °C (hold for 1.5 h) → Heat up to 1000 °C (hold for 10 h) → Cool in the furnace → Take out the mold from the furnace at around 50 °C.

[0129]

Table 4

[0130] The results of observing the mixed powder of sample No. 111 in Table 4 using a scanning electron microscope (SEM) are shown in Fig. 9. The spherical powder indicated by the arrow is pure titanium powder produced by the gas atomization method. Although there are differences in particle size, both powders are mixed relatively uniformly.

[0131] Analysis and appearance observation of the density, relative density, oxygen content, nitrogen content, and hydrogen content of the rectangular titanium sintered body obtained through the above heating and sintering pattern were carried out. The density was measured using the Archimedes method, and the relative density (%) was calculated assuming the specific gravity of pure Ti is 4.51 g / cm 3 and the results are listed in Table 4.

[0132] In samples No. 108 to 111 which are examples of the present invention, the relative density was 85% or more and the appearance of the sintered body was also good. On the other hand, in sample No. 107 which is a comparative example, since the starting material did not contain titanium hydride powder, the progress of the sintering phenomenon was insufficient and the target value of the relative density (85% or more) was not satisfied. In sample No. 112 containing 60% titanium hydride powder in the starting material, a large amount of hydrogen was generated and fine cracks occurred on the surface of the sintered body.

[0133] In samples No. 108 to 112 prepared such that the amount of titanium hydride powder is in a mass ratio of 10% to 60%, the hydrogen content remaining in the sintered body is 0.009 mass% or less, satisfying the JIS standard (H ≦ 0.013 mass%).

[0134] [Test 4]

[0135] High-hydrogen titanium powder prepared so that the hydrogen content in the titanium hydride powder is in the range of 0.8 to 1.5% by mass, and low-hydrogen titanium powder (pure titanium powder) with an unavoidably contained amount of hydrogen in the powder (0.01 to 0.08% by mass) were prepared as starting materials.

[0136] The hydrogen, oxygen, and nitrogen contents in the prepared titanium hydride powder and pure titanium powder are shown in Table 5 below.

[0137]

Table 5

[0138] Starting material powders with different blending ratios of titanium hydride powder and pure titanium powder were filled into a non-sealed type mold, and sintered under a vacuum atmosphere without pressurizing the starting material powders according to the following heating and sintering pattern.

[0139] Heating and sintering pattern:

[0140] Room temperature → (20°C / min) → 650°C × 2 h → (20°C / min) → 1000°C × 10 h → Furnace cooling

[0141] The density, relative density, oxygen amount, nitrogen amount, and hydrogen amount of the sintered body after sintering were measured, and the appearance of the sintered body was further observed. The results are shown in Table 6 below.

[0142]

Table 6

[0143] The hydrogen content in the prepared titanium hydride powder is 0.922 mass% within the range of 0.8 to 1.5 mass%. Focusing on the relative density, the relative density of the sintered bodies of Sample Nos. 202 to 206, in which the hydrogen content in the starting material powder is within the range of 0.20 to 1.0 mass%, satisfies 85% or more of the target value. The starting material powder of Sample No. 206 is only titanium hydride powder, but since the hydrogen content in the starting material powder is 0.92 mass%, a sintered body with a relative density of 85% or more could be obtained by applying the powder filling sintering method using a non-sealed type mold.

[0144] Focusing on the amount of titanium hydride powder in the starting material powder, those satisfying a relative density of 85% or more are Sample Nos. 202 to 206 with 20 to 100 mass%.

[0145] [Test 5]

[0146] High-hydrogen titanium powder prepared so that the hydrogen content in the titanium hydride powder is within the range of 0.8 to 1.5 mass%, and low-hydrogen titanium powder (pure titanium powder), the amount of hydrogen contained unavoidably in the powder (0.01 to 0.08 mass%), were prepared as starting materials.

[0147] The hydrogen, oxygen, and nitrogen contents in the prepared titanium hydride powder and pure titanium powder are shown in Table 7 below.

[0148]

Table 7

[0149] Starting material powders with different blending ratios of titanium hydride powder and pure titanium powder were filled into a non-sealed type mold, and sintered under the following heating and sintering pattern in a vacuum atmosphere without applying pressure to the starting material powder.

[0150] Heating and sintering pattern:

[0151] Room temperature → (20°C / min) → 650°C × 2 h → (20°C / min) → 1000°C × 10 h → Furnace cooling

[0152] The density, relative density, oxygen content, nitrogen content, and hydrogen content of the sintered body after sintering were measured, and the appearance of the sintered body was further observed. The results are shown in Table 8 below.

[0153]

Table 8

[0154] The hydrogen content in the prepared titanium hydride powder is 1.211% by mass within the range of 0.8 to 1.5% by mass. Focusing on the relative density, the relative density of the sintered bodies of Samples No. 302 to 306 in which the hydrogen content in the starting material powder is within the range of 0.25 to 1.21% by mass satisfies 85% or more of the target value. Although the starting material powder of Sample No. 306 is only titanium hydride powder, since the hydrogen content in the starting material powder is 1.21% by mass, a powder filling sintering method using a non-sealed type mold was applied to obtain a sintered body with a relative density of 85% or more.

[0155] Focusing on the amount of titanium hydride powder in the starting material powder, Samples No. 302 to 306 with 20 to 100% by mass satisfy a relative density of 85% or more.

[0156] [Experiment with varying the particle size of high-hydrogen titanium powder]

[0157] Experiments were conducted by varying the particle size of the high-hydrogen titanium powder used under the same heating and sintering conditions as in Test 1.

[0158] The following three types of hydrogenated pure titanium powders were used for comparison.

[0159] a) Hydrogenated pure titanium powder with an average particle size of 10 μm or less (hydrogen content: 2.0 to 4.0% by mass)

[0160] b) Hydrogenated pure titanium powder with an average particle size exceeding 10 μm and 45 μm or less (hydrogen content: 2.0 to 4.0% by mass)

[0161] c) Hydrogenated pure titanium powder with an average particle size exceeding 45 μm and not exceeding 150 μm (hydrogen content: 2.0 to 4.0 mass%)

[0162] Amount of hydrogenated pure titanium powder in the mixed powder: 40 mass%

[0163] The results are shown in Table 9 below.

[0164]

Table 9

[0165] The relative densities of the sintered compacts of Sample No. 3 and Sample No. 7 with an average particle size of the hydrogenated titanium powder of 45 μm or less were 92.5 to 94.6%. The tensile strength after rolling of Sample No. 3 was 798 MPa, and the elongation at break was 30.0%. Sample No. 3 and Sample No. 7 can be used as practically effective titanium sintered materials.

[0166] The relative density of the sintered compact of Sample No. 8 with an average particle size of the hydrogenated titanium powder exceeding 45 μm was 90.4%, and this value was higher than that of the sintered compact of Sample No. 1 consisting only of low-hydrogen titanium powder. However, compared with Sample No. 3 and Sample No. 7 using fine hydrogenated titanium powder, the properties of the tensile strength and elongation at break after rolling were inferior.

[0167] From the above results, if more importance is attached to the properties of the tensile strength and elongation at break after rolling, it is considered desirable to use hydrogenated titanium powder with an average particle size of 45 μm or less.

[0168] [Comparison with the conventional manufacturing method]

[0169] The mold powder filling sintering method of the present invention is characterized in that no compression processing is performed on the starting raw material powder. For comparison, a compression solidified body was created by pressurizing with a cold isostatic pressing method (CIP), which is one of the conventional manufacturing methods, and a sintered body obtained by sintering this compression solidified body was produced. The size and heat treatment pattern of the sintered body were made the same as those of the mold powder filling sintering method of the present invention in Test 1.

[0170] The powders used are as follows.

[0171] a) Hydrogenated pure titanium powder with an average particle size of 10 μm or less

[0172] b) Dehydrogenated pure titanium powder with an average particle size exceeding 10 μm and 45 μm or less

[0173] The results are shown in Table 10 below.

[0174]

Table 10

[0175] Focusing on sample No. 9 sintered after CIP forming, the amount of titanium hydride powder in the whole mixed powder is 40% by mass, corresponding to sample No. 3 prepared by the method of the present invention. Comparing sample No. 3 and sample No. 9, the density of the CIP formed body of sample No. 9 is considerably higher than the density of the packed powder of sample No. 3. However, looking at the relative density of the sintered body, there is no significant difference between the two. In the method of the present invention, the density of the sintered body is high without pressurizing the packed powder, which can be seen to be because sintering is promoted by utilizing the high-speed diffusibility of hydrogen dissociated by the decomposition of TiH 2 .

[0176] Samples No. 10 and 11 correspond to samples No. 5 and 6 prepared by the method of the present invention in terms of the mixing ratio of the mixed powder. The sintered bodies of samples No. 10 and 11 cracked during sintering, similar to samples No. 5 and 6.

[0177] From the results in Table 10, it is recognized that the mold powder filling sintering method without creating a compression solidified body can produce a sintered material equivalent in characteristics to the conventional manufacturing method of producing a compression solidified body by CIP forming and then sintering. According to the present invention, since a press, CIP equipment, or HIP equipment is not required, a significant reduction in equipment costs can be achieved compared to the conventional manufacturing method.

[0178] [Atmosphere during sintering treatment]

[0179] Sample No. 3 (40% hydrogenated pure titanium powder + dehydrogenated pure titanium powder) was heated and sintered in a vacuum atmosphere. The mixed powder with the same mixing ratio as Sample No. 3 was heated and sintered with the heating and sintering atmosphere changed to an Ar gas atmosphere (non-vacuum atmosphere). The results are shown in Table 11 below.

[0180]

Table 11

[0181] In the sintered body of Sample No. 3 processed in a vacuum atmosphere, the hydrogen content in the sintered body composition was 0.005% by mass, and the relative density was 94.6%. The tensile strength after rolling was 798 MPa, and the elongation at break was 30.0%.

[0182] In the case of the sintered body of Sample No. 12 processed in an Ar gas atmosphere, after sintering in an Ar gas atmosphere, a dehydrogenation treatment was performed for 50 hours. Finally, the hydrogen content in the obtained sintered body composition was 0.007% by mass, and the relative density was 92.5%. The tensile strength after rolling was 724 MPa, and the elongation at break was 31.8%. From looking at these properties, it is recognized that the titanium sintered material of Sample No. 12 heated and sintered in an Ar gas atmosphere can also be effectively utilized in practical applications.

[0183] It is considered that good sintered body density can be obtained even when heating and sintering in a non-vacuum atmosphere such as Ar gas because, as shown in Fig. 11, the shielding effect of the hydrogen gas generated by the decomposition of TiH2 suppresses the mixing of oxygen into the titanium material.

[0184] [Presence or absence of the lid of the mold]

[0185] The non-sealed type mold used in the mold powder filling sintering method of the present invention may be open at the top (without a lid) or may have a lid at the top. It was confirmed whether there is a significant difference in the properties of the sintered material after heating and sintering depending on the presence or absence of the lid.

[0186] Two types of powders, pure titanium hydride powder and dehydrogenated pure titanium powder, were prepared as starting materials. In one of the mixed powders, the amount of pure titanium hydride powder was adjusted to 20% by mass based on the total amount of the mixed powder, and in the other mixed powder, the amount of pure titanium hydride powder was adjusted to 50% by mass based on the total amount of the mixed powder.

[0187] The two types of mixed powders were respectively heat-sintered using a mold without a lid and a mold with a lid. The heating and sintering conditions were the same as those for Samples No. 1 to 6.

[0188] The results are shown in Table 12 below.

[0189]

Table 12

[0190] Focusing on Sample No. 13 and Sample No. 14 in which the ratio of pure titanium hydride powder is 20% by mass, the relative density of the sintered body of Sample No. 13 sintered with a mold with a lid is 91.7%, and the relative density of the sintered body of Sample No. 14 sintered with a mold without a lid is 90.7. The difference in this density is only 1%, and no significant difference is observed between the two.

[0191] Similarly, focusing on Sample No. 15 and Sample No. 16 in which the ratio of pure titanium hydride powder is 50% by mass, the relative density of the sintered body of Sample No. 15 sintered with a mold with a lid is 95.6%, and the relative density of the sintered body of Sample No. 16 sintered with a mold without a lid is 92.0%. This difference is 3.6% and is somewhat large, but if the relative density is 92.0%, it is sufficiently high for practical use.

[0192] Figure 10 is a photograph showing the sintered body after sintering of Sample No. 16. As is clear from this photograph, a gap is formed between the sintered body and the inner surface of the mold without a lid, and it is recognized that the mixed powder as the starting material has shrunk in volume by solid-phase sintering using the high diffusibility of hydrogen.

[0193] [Sample containing titanium alloy powder as starting material]

[0194] Regarding the mold powder filling and sintering method using the unsealed type mold of the present invention, tests (Test 6 and Test 7) were conducted to confirm that good sintered bodies can also be obtained for samples containing titanium alloy powder as starting materials.

[0195] [Test 6]

[0196] The prepared starting materials are two types, hydrogenated pure titanium powder and 64 titanium (Ti-6Al-4V) alloy powder. For these two types of mixed powders, heating and sintering were performed using an unsealed type mold with different blending ratios. The heating and sintering conditions are the same as those for Samples No. 1 to 6. The results are shown in Table 13 below.

[0197] In Table 13, the relative densities of the filled powder and the sintered body are calculated based on the calculated values according to the mixing ratio, assuming the specific gravity of pure titanium is 4.51 g / cm 3 , and the specific gravity of the titanium alloy is 4.43 g / cm 3 . The reference specific gravity is described in Table 13 and Table 14 to be described later.

[0198]

Table 13

[0199] The relative density of the sintered body of Sample No. 17, in which the amount of hydrogenated pure titanium powder is 20% by mass with respect to the entire mixed powder, is 90.0%. As described above, in Sample No. 2, hydrogenated pure titanium powder and pure titanium powder were mixed, and the amount of hydrogenated pure titanium powder was 20% by mass with respect to the entire mixed powder, and the relative density of the sintered body was 94.3%.

[0200] The relative density of the sintered body of Sample No. 18, in which the amount of hydrogenated pure titanium powder is 40% by mass with respect to the entire mixed powder of hydrogenated pure titanium powder and 64 titanium alloy powder, is 91.3%. Sample No. 3 described above is a mixed powder of hydrogenated pure titanium powder and pure titanium powder, and the amount of hydrogenated pure Titanium powder is 40% by mass, and the relative density of the sintered body was 94.6%.

[0201] Regarding Sample No. 19, in which the amount of hydrogenated pure titanium powder is 60% by mass with respect to the entire mixed powder of hydrogenated pure titanium powder and 64 titanium alloy powder, similar to Sample No. 5 described above (a mixed powder of hydrogenated pure titanium powder and pure titanium powder, and the amount of hydrogenated pure titanium powder is 60% by mass), cracks occurred in the sample during the sintering process, so the relative density was not measured.

[0202] From the test results of Samples No. 17 to 19, it was confirmed that the mold powder filling sintering method using the non-sealed type mold of the present invention is equally applicable to those using hydrogenated pure titanium powder and titanium alloy powder as starting materials, and a sintered body with a high relative density can be obtained if the ratio of hydrogenated pure titanium powder is less than about 60%.

[0203] [Test 7]

[0204] The prepared starting materials are two types, namely hydrogenated titanium alloy (Ti-6Al-4V) powder and dehydrogenated pure titanium powder. For these two types of mixed powders, heating sintering was carried out using a non-sealed type mold while changing the blending ratio. The heating and sintering conditions are the same as those of Samples No. 1 to 6. The results are shown in Table 14 below.

[0205]

Table 14

[0206] The relative density of the sintered body of Sample No. 20, in which the amount of the titanium hydride alloy powder is 20% by mass with respect to the total amount of the mixed powder of the titanium hydride alloy powder and the pure titanium powder, is 92.7%. Sample No. 2 described above had a relative density of the sintered body of 94.3% with the amount of the hydrogenated pure titanium powder being 20% by mass with respect to the total amount of the mixed powder of the hydrogenated pure titanium powder and the pure titanium powder.

[0207] The relative density of the sintered body of Sample No. 21, in which the amount of the titanium hydride alloy powder is 40% by mass with respect to the total amount of the mixed powder of the titanium hydride alloy powder and the pure titanium powder, is 90.2%. Sample No. 3 described above had a relative density of the sintered body of 94.6% with the amount of the hydrogenated pure titanium powder being 40% by mass with respect to the total amount of the mixed powder of the hydrogenated pure titanium powder and the pure titanium powder.

[0208] From the test results of Samples No. 20 to 21, it was confirmed that the mold powder filling sintering method using the non-sealed type mold of the present invention is equally applicable to those using the titanium hydride alloy powder and the pure titanium powder as starting materials.

[0209] From Test 6 and Test 7, it was confirmed that the mold powder filling sintering method using the non-sealed type mold of the present invention can also obtain a good sintered body for samples containing a titanium alloy powder as a starting material.

[0210] As described above, the embodiments of the present invention have been described with reference to the drawings. However, the present invention is not limited to the embodiments described herein, and various modifications can be made within the scope identical or equivalent to the invention described in the claims.

Industrial Applicability

[0211] The present invention can be advantageously used as a method for manufacturing a titanium sintered material.

Claims

Step of preparing high-hydrogen titanium powder containing a titanium hydride compound in a hydrogenated state and having a hydrogen content of 2.0 to 4.0% by mass. Step of preparing low-hydrogen titanium powder which has not been hydrogenated or has been dehydrogenated after hydrogenation and has a hydrogen content of 0.01 to 0.08% by mass. Step of mixing the high-hydrogen titanium powder and the low-hydrogen titanium powder and preparing a titanium-based starting material powder adjusted so that the hydrogen content of the entire mixed powder is 0.2 to 2.0% by mass. Step of filling the non-sealed type mold with the titanium-based starting material powder. Step of obtaining a titanium sintered material by heating and sintering the titanium-based starting material powder in the mold without applying pressure. The heat sintering of the titanium-based starting material powder in the mold is as follows: Raising the temperature from room temperature to an intermediate temperature range where hydrogen in the titanium-based starting material powder is dissociated from titanium. Holding the titanium-based starting material powder in the intermediate temperature range to dissociate hydrogen from titanium, and promoting sintering between powder particles by utilizing the high diffusibility of the dissociated hydrogen. Raising the temperature of the titanium-based starting material powder from the intermediate temperature range to a high temperature range where sintering of the titanium-based starting material powder is performed. Holding the titanium-based starting material powder in the high temperature range to complete sintering. A method for producing a titanium sintered material, including cooling the sintered body after sintering from the high temperature range to room temperature.

2. The method for producing a titanium sintered material according to claim 1, wherein the amount of the high-hydrogen titanium powder with respect to the entire mixed powder is 10 to 55% by mass.

3. The hydrogen content in the high-hydrogen titanium powder is 0.8 to 1.5% by mass. The method for producing a titanium sintered material according to claim 1, wherein the amount of the high-hydrogen titanium powder with respect to the entire mixed powder is 20% by mass or more and less than 100% by mass.

4. The method for producing a titanium sintered material according to claim 1, wherein the titanium-based starting material powder is made of pure titanium substantially containing only titanium as a metal element.

5. The method for producing a titanium sintered material according to claim 1, wherein at least one of the high-hydrogen titanium powder and the low-hydrogen titanium powder is made of a titanium alloy containing titanium as a main component.

6. The intermediate temperature range is within the range of 550°C to 850°C. The method for producing a titanium sintered material according to claim 1, wherein the high temperature range is within the range of 850°C to 1400°C.

7. The intermediate temperature zone has a low-temperature-side intermediate temperature zone and a high-temperature-side intermediate temperature zone, The titanium-based starting material powder is heated to the high-temperature-side intermediate temperature zone after being held in the low-temperature-side intermediate temperature zone, and then heated to the high-temperature zone after being held in the high-temperature-side intermediate temperature zone. The method for producing a titanium sintered material according to claim 1.

8. The method for producing a titanium-based sintered material according to claim 1, wherein the heating and sintering of the titanium-based starting material powder in the mold is performed in a non-vacuum atmosphere.

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