JP7690206B2 - Manufacturing method of titanium sintered material - Google Patents

Description

This invention relates to a method for producing titanium sintered material by powder metallurgy.

Titanium is a lightweight material with a specific gravity about half that of steel, and has excellent corrosion resistance and strength properties, so it is used in parts for aircraft, railway cars, motorcycles, automobiles, and other vehicles where there is a strong need for weight reduction, as well as in home appliances and building materials. In addition, because of its excellent corrosion resistance, titanium is also used as a medical material.

Titanium materials are manufactured by a powder metallurgy method using titanium powder as a starting material, as described in, for example, JP 2017-88908 A (Patent Document 1). The manufacturing method of titanium sintered material disclosed in this Patent Document 1 includes the following steps.
a) mixing a titanium component powder with nitride particles of a metal other than titanium;
b) A process of applying a compressive force to the mixed powder to form a compact.
c) A step of heating and sintering the compression molded body obtained by compression molding in an oxygen-free vacuum atmosphere.

Titanium powder (pure titanium powder or titanium alloy powder) as a starting material is expensive compared to iron-based and aluminum-based materials.

Patent Publication No. 3459342 (Patent Document 2) describes a method in which titanium or a titanium alloy is hydrogenated by utilizing the hydrogen embrittlement of the titanium or titanium alloy, and then pulverized to a desired particle size to produce hydrogenated titanium powder, and a hydrogenation/dehydrogenation method in which this is dehydrogenated by vacuum heating to convert it into titanium powder.

High-concentration hydrogen-containing titanium powder containing titanium hydride (TiH ₂ ) compounds as hydrogenated (hereinafter referred to as "high-hydrogen titanium powder" or "hydride titanium powder") has a lower market price than dehydrogenated titanium powder. Hydrogenated fine titanium powder with a particle size of 10 μm or less has a large specific surface area and absorbs a large amount of oxygen from the air due to the processing heat during grinding, so hydrogenated titanium powder with a particle size of 10 μm or less is not usually used as an alloy raw material.

Japanese Patent Laid-Open Publication No. 2020-63509 (Patent Document 3) proposes a method for providing a high-strength and high-toughness titanium sintered material while reducing production costs by actively utilizing titanium hydride powder with a particle size of 10 μm or less, which is usually discarded. Specifically, the method for producing a titanium sintered material disclosed in Patent Document 3 includes the following steps.
d) Mixing the fine titanium hydride powder with larger particle size titanium powder.
e) A step of compressing and molding the mixed powder to obtain a compact.
f) A process of subjecting the compacted body to a dehydrogenation treatment and then sintering the compacted body under vacuum.

In the manufacturing method of titanium sintered material described in Patent Document 1, Patent Document 3, etc., a mixed powder of starting materials is pressurized in a press to produce a compressed solidified body, which is then sintered under vacuum. A different manufacturing method of titanium sintered material to the above method is to solidify titanium powder or mixed powder using hot isostatic pressing (HIP) or cold isostatic pressing (CIP), and then sinter the solidified body under vacuum.

The paper "Powder Metallurgy of Titanium-Past, Present and Future" (INTERNATIONAL MATERIALS REVIEW, 2017) by Zhigang Zak Fang et al. describes the advantages of using titanium hydride powder. Specifically, it describes how the brittle titanium hydride powder is crushed into fine particles during the press molding process, which fill the gaps between the titanium powder particles and improve the density of the compact. It also describes how the hydrogen in the titanium powder diffuses at high speed, improving sinterability.

In the method of manufacturing titanium sintered material described in Non-Patent Document 1, a mixed powder containing titanium hydride powder is compressed and solidified by hot isostatic pressing (HIP) or cold isostatic pressing (CIP), and this compressed and solidified body is then sintered under vacuum.

JP 2017-88908 A Patent No. 3459342 JP 2020-63509 A

Zhigang Zak Fang et al.'s paper "Powder metallurgy of titanium - past, present and future" (INTERNATIONAL MATERIALS REVIEW, 2017)

A common feature of conventional manufacturing methods for sintered titanium material is that raw material powder is compressed to produce a compressed solid, which is then heated and sintered in a vacuum atmosphere. The raw material powder is compressed in order to reduce voids between the powder particles, increase the contact area between the powder particles, and improve sintering properties. Sintering in a vacuum atmosphere is also done to prevent oxygen from being introduced into the sintered body.

The problem with the conventional manufacturing method is that presses, HIP equipment, CIP equipment, etc. are required to produce a compressed solidified body of titanium powder or raw material powder, which increases equipment costs. In addition, batch-type vacuum sintering equipment is required to suppress the incorporation of oxygen, which reduces productivity and ultimately increases manufacturing costs.

The object of the present invention is to provide a method for producing titanium sintered material that can reduce production costs.

A method for producing a titanium sintered material according to the present invention comprises the following steps.
a) preparing a titanium-based starting raw material powder adjusted so that the hydrogen content relative to the total amount of the powder is 0.2 to 2.0 mass %;
b) A step of filling the titanium-based starting material powder into a non-sealed mold.
c) A process of heating and sintering the titanium-based starting raw material powder in the mold without applying pressure to obtain a titanium sintered material.

The titanium-based starting raw material powder may be one type of powder or a mixture of multiple types of powder. Furthermore, the terms "titanium-based" and "titanium" used in this specification include both pure titanium, which is essentially composed of titanium as the metallic element, and titanium alloys that contain titanium as the main metallic element.

In one preferred embodiment, the titanium-based starting material powder is a mixed powder of high-hydrogen titanium powder, which intentionally contains hydrogen, and low-hydrogen titanium powder, which unavoidably contains hydrogen.

In the above preferred embodiment, the high-hydrogen titanium powder is a high-concentration hydrogen-containing titanium powder (hydrogenated titanium powder) containing a titanium hydride (TiH ₂ ) compound that has been subjected to hydrogenation treatment, and the low-hydrogen titanium powder is a titanium powder that has not been subjected to hydrogenation treatment or that has been subjected to dehydrogenation treatment after hydrogenation treatment. An example of the low-hydrogen titanium powder that has not been subjected to hydrogenation treatment is an atomized powder.

The hydrogen content in titanium hydride powder is generally 2.0 to 4.0 mass%, and the hydrogen content in low-hydrogen titanium powder, which inevitably contains hydrogen, is generally 0.01 to 0.08 mass%. In this case, the amount of high-hydrogen titanium powder relative to the total mixed powder is preferably 10 to 55 mass%.

In another embodiment, the hydrogen content in the titanium hydride powder is adjusted to 0.8 to 1.5 mass%. The hydrogen content in the low hydrogen titanium powder is 0.01 to 0.08 mass%. In this case, the amount of high hydrogen titanium powder relative to the total mixed powder is preferably 20 mass% or more and less than 100 mass%.

In yet another embodiment, the titanium-based starting raw material powder consists solely of high-hydrogen titanium powder that has been intentionally prepared to have a hydrogen content of 0.8 to 1.5 mass%.

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

In other embodiments described herein, 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. Both the high hydrogen titanium powder and the low hydrogen titanium powder may be made of a titanium alloy.

The heat sintering, which is carried out without applying pressure to the titanium-based starting material powder in the mold, utilizes the high-speed diffusion of hydrogen decomposed from _TiH2 contained in large amounts in the starting material powder. Therefore, even if a compressed solid is not prepared before sintering, solid-phase sintering at the interfaces between adjacent powder particles proceeds smoothly, improving sinterability.

The titanium-based starting powder material in the mold can be heated and sintered in a vacuum or non-vacuum atmosphere. The shielding effect of hydrogen gas generated from inside the starting powder material prevents oxygen from being mixed into the titanium material, so good sintering can be achieved even in a non-vacuum atmosphere.

Heating and sintering the titanium-based starting material powder in the mold may, for example, include the following:
d) Raising the temperature from room temperature to an intermediate temperature range where hydrogen in the starting raw material powder is dissociated from titanium.
e) The titanium-based starting raw material powder is maintained in the above-mentioned intermediate temperature zone to dissociate hydrogen from the titanium, and sintering between the powder particles is promoted by utilizing the high-speed diffusivity of the dissociated hydrogen.
f) Raising the temperature of the titanium-based starting material powder from an intermediate temperature zone to a high temperature zone for sintering the titanium-based starting material powder.
g) maintaining the titanium-based starting material powder in a high temperature zone to complete sintering;
h) Cooling the sintered body after sintering is completed from the high temperature zone to room temperature.

The intermediate temperature zone is preferably in the range of 550°C to 850°C. The high temperature zone is in the range of 850°C to 1400°C. In one embodiment, the intermediate temperature zone has a low-temperature side intermediate temperature zone and a high-temperature side intermediate temperature zone, and the titanium-based starting raw material powder is held in the low-temperature side intermediate temperature zone and then heated to the high-temperature side intermediate temperature zone, and is held in the high-temperature side intermediate temperature zone and then heated to the high-temperature side intermediate temperature zone.

When the titanium-based starting raw 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.

In one embodiment, the high hydrogen titanium powder and the low hydrogen titanium powder are made of pure titanium that contains substantially only titanium as a metallic element. In this embodiment, a small amount of iron (Fe) powder may be further added to the above mixed powder.

In another embodiment, 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. For example, titanium alloy 64 (Ti-6Al-4V) is used as the titanium alloy.

According to the present invention, titanium-based starting raw material powder, which has been prepared so that the hydrogen content of the entire powder is 0.2 to 2.0 mass%, is placed in a non-sealed mold and heated and sintered in the mold without pressure. This utilizes the high-speed diffusion of decomposed hydrogen to improve the solid-phase sintering between the powder particles, eliminating the need for conventional presses, CIP equipment, or HIP equipment, and allowing for significant reductions in equipment costs.

3 is a photograph showing raw material powder filled in a mold before sintering and the sintered material after sintering. 4 is a photograph showing the top, center, and bottom portions of a vertical cross section of a sintered material after sintering. Photographs showing two sintered materials sintered at different heating rates. 13 is a photograph of a sintered material sintered under the conditions described in Verification 4. 1A and 1B are diagrams showing examples of the structure of a non-sealing type mold. 4 is a photograph showing the structure of a sintered material after sintering. 1 is a scanning electron microscope photograph of the mixed powder of Sample No. 105 in Table 3. 1 is an optical microscope photograph of the structure of sintered bodies of Sample No. 101 (Comparative Example) and Sample No. 104 (Example). 1 is a scanning electron microscope photograph of the mixed powder of Sample No. 111. 1 is a photograph showing a sintered body of Sample No. 16 after sintering. FIG. 1 is a diagram for explaining the shielding effect of hydrogen gas generated by decomposition of TiH ₂ .

The inventors of the present application conducted various experiments, thinking that when hydrogen is contained in excess in titanium powder, a dense solid-phase sintered body can be obtained by utilizing the high-speed diffusion of hydrogen. The data will be presented and explained in detail later, but in conclusion, they found that if the hydrogen content in the titanium powder as the starting material is adjusted to an appropriate range, the powder is placed in a non-sealed mold, and the powder is heated and sintered under appropriate conditions, the hydrogen generated by the decomposition of _TiH2 diffuses rapidly between the titanium powder particles, and the titanium components also diffuse between the powder particles, promoting solid-phase sintering. They also found that a dense sintered material can be obtained without applying pressure to the titanium-based starting material powder in the mold. They also found that sintering in a non-vacuum atmosphere is possible because the shielding effect of the hydrogen gas generated from inside the titanium powder during the heat treatment suppresses the intrusion of oxygen into the titanium material. As a result, continuous non-vacuum sintering equipment can be used instead of the conventional batch-type vacuum sintering equipment, which has the economic advantage of reducing the cost of the sintering process.

The following points are important factors for obtaining titanium sintered material using the rapid diffusion of hydrogen:

a) Use of non-sealed type molds

b) Use of high hydrogen titanium powder

c) Mixing ratio of high hydrogen titanium powder to low hydrogen titanium powder

d) A slow heating rate to prevent the rapid release of hydrogen from the titanium powder.

e) Holding at intermediate temperature to fully decompose _TiH2

f) Holding at high temperatures to ensure sufficient sintering.

[Basic verification experiment of powder packing sintering method using small mold]

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

A titanium-based starting raw material powder consisting only of hydrogen-treated high-hydrogen titanium powder was filled into an open-top alumina mold measuring 120 mm x 120 mm in length and width, and the temperature was raised from room temperature to 1000°C in a vacuum atmosphere without applying pressure. The material was sintered by holding it at 1000°C for 24 hours, and then cooled in a furnace.

The hydrogen content in commercially available high-hydrogen titanium powder that has been hydrogenated is generally 2.0 to 4.0 mass%.

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

As a result, the alumina mold filled with starting material powder consisting only of high hydrogen titanium powder was broken. On the other hand, the alumina mold filled with starting material powder consisting only of low hydrogen titanium powder was not broken. The reason for this is thought to be that when starting material powder consisting only of high hydrogen titanium powder was used, the sintering progress body expanded during the heating process and sintering process due to the decomposition of _TiH2 and the release of hydrogen, destroying the alumina mold.

From the above verification, it has been found that in order to avoid a sudden volume expansion of the sintering progress body, it is desirable to adjust the hydrogen content in the titanium-based starting raw material powder to be within an appropriate range, that when the hydrogen content in the high-hydrogen titanium powder is 2.0% or more, it is desirable to use a starting raw material powder that is a mixture of high-hydrogen titanium powder and low-hydrogen titanium powder rather than using 100% high-hydrogen titanium powder, that it is desirable to avoid a sudden increase in temperature or heating in order to suppress the sudden decomposition of _TiH2 and the sudden release of hydrogen, and that it is desirable to use a high-strength mold (e.g., made of stainless steel) that can withstand the volume expansion of the sintering progress body.

[Verification 2: Accelerated sintering due to rapid hydrogen diffusion]

Pure titanium powder and hydrogenated pure titanium powder were prepared as starting materials, and the amount of hydrogenated pure titanium powder was adjusted to 30 mass% of the total mixed powder. 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 mass%. The hydrogen content in the hydrogenated pure titanium powder was in the range of 2.0 to 4.0 mass%.

A metal mold (50 mm x 70 mm x 10 mmH) with an open top was prepared as a small mold.

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 pressurization, 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 a furnace. The intermediate temperature of 600°C was held for about 1.5 hours in order to fully decompose _TiH2 in this temperature range and effectively utilize the high-speed diffusivity of the dissociated hydrogen.

The hydrogen content in the raw 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. After sintering, the hydrogen content in the sintered material was 0.009% by mass, the oxygen content was 0.409% by mass, and the nitrogen content was 0.028% by mass.

Figure 1 is a photograph showing the raw material powder before sintering filled in a mold and the sintered material after sintering. The amount of hydrogenated pure titanium powder relative to the total raw material powder before sintering was 30 mass%, and the hydrogen content in the total raw material powder was 1.105 mass%.

There was a gap between the sintered material and the inner surface of the mold after sintering, and it was confirmed that the raw material powder had shrunk during the sintering process to become the sintered material. The shrinkage rate was 14.3%. The weight of the sintered material was 3.85 g per ^cm3 , and the relative density was 86.5%.

Figure 2 is a photograph showing the top, center, and bottom of the longitudinal section of the sintered material after sintering. It can be seen that there are no voids in the center, and the density is high. This is because hydrogen generated by the decomposition of _TiH2 diffuses between the powder particles at high speed, promoting solid-phase sintering between the titanium particles.

Many voids can be seen on the top and bottom surfaces, which are believed to have been formed when hydrogen gas escaped to the outside. If the heating rate during the sintering process is too high, a large amount of hydrogen will escape from the raw powder, which is thought to interfere with sintering, which utilizes the high-speed diffusion of hydrogen.

[Verification 3: Heating rate]

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 high-hydrogen pure titanium powder that had been hydrogenated, and the amount of high-hydrogen pure titanium powder relative to the total mixed powder was adjusted to 30 mass%. The hydrogen content relative to the total mixed powder was 0.8 mass%. Photograph (a) shows a titanium sintered material produced at a heating rate of 50°C/min during the heat sintering process, and photograph (b) shows a titanium sintered material produced at a heating rate of 20°C/min. Comparing the two photographs, it is clear that the higher the heating rate, the more likely cracks are to occur.

[Verification 4: Strength characteristics of sintered materials obtained by powder packing sintering method using a mold]

The starting material was prepared by mixing low hydrogen pure titanium powder and high hydrogen pure titanium powder, with the amount of high hydrogen pure titanium powder being 40% by mass relative to the total mixed powder. The starting material powder was filled into a mold, and heated from room temperature to 600°C at a heating rate of 10-20°C/min in a vacuum atmosphere without pressure, and held at 600°C for 1.5 hours, then heated to 1000°C at a heating rate of 10-20°C/min, and held at 1000°C for 2 hours for sintering, after which it was cooled in a furnace to obtain a sintered material. The hydrogen content of the entire starting material powder was 1.13% by mass.

Figure 4 is a photograph of the sintered material sintered under the above conditions. As is clear from the photograph, the sintered material was free of internal cracks and had a relative density of 89.5%.

The sintered material obtained as described above was subjected to hot plastic processing to produce prototype materials for strength testing. A comparison of the properties of the prototype materials and JIS Type 4 pure titanium is shown in Table 1.

As can be seen from Table 1, the prototype material is superior to JIS Class 4 pure titanium in terms of tensile yield strength, tensile strength, and breaking elongation.

[Verification 5: Mold structure]

The mold for filling the starting raw material powder can be of any non-sealed type, and we confirmed that one with the structure shown diagrammatically in Figure 5 can be used.

In Figure 5, (a) shows an open-top mold, and (b) shows an open-top mold with a lid placed on top of the raw material powder filled in it. There is a gap between the lid and the inner wall surface of the mold. (c) shows an open-top mold with a lid placed on the top end surface of the side wall, and there is a small gap between the lid and the top end surface of the side wall of the mold. The advantage of using a lid is that it prevents the powder inside the mold from flying around.

The mold structures shown in Figures 5(a), (b), and (c) are illustrative, and structures other than those shown in Figure 5 can be used as long as they are non-sealed type molds.

[Verification 6: Effect of particle size of titanium hydride powder]

As starting materials, pure titanium powder and hydrogenated pure titanium powder were prepared, and the amount of hydrogenated pure titanium powder was adjusted to 50 mass% of the total mixed powder. The hydrogenated titanium powders used were prepared with an average particle size of less than 10 μm, an average particle size of 10 to less than 45 μm, and an average particle size of 45 to less than 150 μm.

The starting raw material powder mixture was filled into an open-top mold (91 mm x 91 mm) and heated from room temperature to 600°C without pressure in a vacuum atmosphere (heating rate 10-20°C/min), held at 600°C for 2 hours, then heated 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 a furnace.

Figure 6 shows the structure of the sintered material after sintering, where (a) uses titanium hydride powder with an average particle size of less than 10 μm, (b) uses titanium hydride powder with an average particle size of 10 to less than 45 μm, and (c) uses titanium hydride powder with an average particle size of 45 to less than 150 μm. The density of the sintered material in (a) is 99.8%, with only a few voids present. The density of the sintered material in (b) is 96.2%, with dispersed voids observed. The density of the sintered material in (c) is 82.9%, with the area (volume) of the dispersed voids observed to be larger.

The results shown in Figure 6 indicate that the sintered density can be improved by using fine-grained titanium hydride powder.

[Preferred heating and sintering conditions]

The favorable features of the titanium powder packing sintering method using a non-sealed mold are as follows:

a) Raise the temperature from room temperature to the intermediate temperature range and hold it at the intermediate temperature for a certain period of time.

The reason for holding the intermediate temperature for a certain period of time is to fully decompose _TiH2 and promote sintering by utilizing the high-speed diffusion of dissociated hydrogen. The intermediate temperature range for decomposing _TiH2 is 550°C to 850°C, and although there is no limit to the holding time, it is, for example, about 1 hour to 3 hours.

b) Raise the temperature from the intermediate temperature zone to the high temperature zone and hold it at the high temperature zone for a certain period of time.

The reason for holding the material in the high-temperature zone for a certain period of time is to ensure complete sintering. The appropriate sintering temperature varies depending on the alloy composition. For titanium sintered material, which is mainly composed of titanium, the high-temperature zone for complete sintering is 850°C to 1400°C, and although there is no limit to the holding time, it is, for example, around 2 to 24 hours.

c) Heating rate from room temperature to intermediate temperature and from intermediate temperature to high temperature

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

d) Heating and sintering atmosphere

From the perspective of preventing oxygen from being absorbed into the titanium material, it is desirable to use a vacuum atmosphere for the heating and sintering atmosphere to obtain titanium sintered material, but if the powder packing sintering method uses a non-sealed mold, it is possible to perform sintering while preventing oxygen from being absorbed into the titanium material, even in a non-vacuum atmosphere such as an argon atmosphere. This is because the shielding effect of hydrogen gas generated from inside the titanium material prevents oxygen from being mixed into the titanium material.

[High hydrogen titanium powder]

The high hydrogen titanium powder is a high hydrogen content titanium powder (titanium hydride powder) containing titanium hydride (TiH ₂ ) compound as it is after hydrogenation treatment, and contains a large amount of hydrogen. The hydrogen content in commercially available titanium hydride powder is generally in the range of 2.0 to 4.0 mass%, but it is also possible to intentionally adjust the hydrogen content. In the mold powder filling sintering method of the present invention, the density of the sintered material is expected to improve if finer titanium hydride powder is used, but there is no need to limit the particle size.

The term "titanium powder" as used herein includes not only pure titanium powder, but also titanium alloy powders whose main component is titanium, such as titanium alloy 64 (Ti-6Al-4V).

[Low hydrogen titanium powder]

Low-hydrogen titanium powder includes titanium powder that has been dehydrogenated after hydrogenation, and titanium powder obtained by atomization. In this specification, the term "titanium powder" includes not only pure titanium powder, but also titanium alloy powder containing titanium as the main component. The hydrogen content in low-hydrogen titanium powder is an unavoidable amount, and is generally 0.01 to 0.08 mass%.

[Tests changing the mixing ratio of high hydrogen titanium powder and low hydrogen titanium powder]

[Test 1]

The density and post-rolling properties (tensile strength and elongation at break) of the sintered bodies obtained were measured by changing the compounding ratio of high-hydrogen titanium powder (hydrogen content: 2.0-4.0% by mass) and low-hydrogen titanium powder (hydrogen content: 0.01-0.08% by mass) under the following conditions.

Weight of starting powder: 500g

Inner dimensions of the non-sealed mold used: 101mm x 101mm

Sintering atmosphere: vacuum

Heating and sintering pattern:

Room temperature → Heat to 600°C (hold for 1.5 hours) → Heat to 800°C (hold for 1.5 hours) → Heat to 1000°C (hold for 10 hours) → Cool inside the furnace → Remove the mold from the furnace at around 50°C.

High hydrogen titanium powder used: hydrogenated pure titanium powder with average particle size of 10 μm or less, as hydrogenated.

Low hydrogen titanium powder used: Dehydrogenated pure titanium powder with an average particle size of more than 10 μm and less than 45 μm

Density measurement: Archimedes method, which corresponds to the "weighing method in liquid" described in JIS Z8807.

Calculation of relative density (%): Calculation was made assuming the specific gravity of pure Ti to be 4.51 g/ ^cm3

The results are shown in Table 2 below.

Looking at samples No. 2 to 4, in which the ratio of titanium hydride powder (high hydrogen titanium powder) to the total mixed powder was 20 to 50 mass%, the hydrogen content in the mixed powder was 0.666 mass% to 1.707 mass%, and the relative density of the sintered body was 94.3 to 96.2%. Furthermore, the tensile strength after rolling of samples No. 2 to 3 was 702 to 798 MPa, and the breaking elongation was 30.0 to 30.3%. These relative densities and post-rolling properties are values that allow the material to be used as a practically effective titanium sintered material. A relative density of 85% or more is desirable for a practically effective titanium sintered material.

The hydrogen content in the starting powder material of sample No. 1, which did not contain titanium hydride powder, was 0.012 mass%, and the relative density of the sintered body was 88.1%.

From samples No. 1 to 4, it can be seen that the density of the sintered body is improved by including titanium hydride powder as the starting raw material powder and setting the hydrogen content in the mixed powder to 0.6 mass% or more.

In samples No. 5 and No. 6, the amount of titanium hydride powder in the mixed powder is 60 mass% or more, and the hydrogen content in the mixed powder exceeds 2.0%. The sintered bodies of samples No. 5 and No. 6 were cracked during the sintering process, so the relative density was not measured. From these results, it seems that in order to prevent cracking of the sintered body, it is desirable to keep the hydrogen content in the mixed powder at 2.0 mass% or less.

In addition, when the hydrogen content in the high-hydrogen titanium powder is 2.0-4.0 mass% and the hydrogen content in the low-hydrogen titanium powder is an unavoidable amount (0.01-0.08 mass%), it is found that it is desirable to set the amount of high-hydrogen titanium powder to 55 mass% or less of the total mixed powder. In Test 1, the lower limit of the amount of high-hydrogen titanium powder to the total mixed powder was set to 20 mass% (Sample No. 2). The relative density of the sintered body of Sample No. 2 was 94.3%, which is significantly higher than that of Sample No. 1, which does not contain high-hydrogen titanium powder. From the perspective of achieving the target relative density of 85% or more, it seems preferable that the amount of high-hydrogen titanium powder to the total mixed powder be 10 mass% or more.

[Test 2]

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

100 g of each mixed powder was filled into a rectangular mold (non-sealed type mold) with inner dimensions of 50 mm width x 70 mm length, and then the mold was placed in a vacuum heating furnace and heated and sintered according to the following heating and heating pattern.

Heating and sintering pattern:

Room temperature → Heat to 650°C (hold for 1.5 hours) → Heat to 800°C (hold for 1.5 hours) → Heat to 1000°C (hold for 10 hours) → Cool inside the furnace → Remove the mold from the furnace at around 50°C.

Figure 7 shows the results of observing the mixed powder of sample No. 105 in Table 3 using a scanning electron microscope (SEM). Each starting raw material powder (titanium hydride powder and hydrogenated/dehydrogenated pure titanium powder) is produced by mechanical pulverization, so the powder particles have an angular shape. The relatively coarse powder indicated by the arrow in Figure 7 is titanium hydride powder. Although there is a difference in particle size, the two powders are mixed relatively uniformly.

The rectangular titanium (Ti) sintered bodies obtained through the heating and sintering pattern were analyzed for density, relative density, oxygen content, nitrogen content, and hydrogen content, and their appearance was observed. The density was measured using the Archimedes method, and the relative density (%) was calculated based on the specific gravity of pure Ti being 4.51 g/ ^cm3 . The results are shown in Table 3.

In samples No. 102 to 105 (examples of the present invention) in which the ratio of titanium hydride powder to the total mixed powder was 10 to 50 mass%, the relative density was 85% or more, and the appearance of the sintered body was also good.

In sample No. 101, which serves as a comparative example, the starting material did not contain titanium hydride powder, so the sintering process did not proceed sufficiently, the target value for relative density (85% or more) was not met, and the occurrence of a recess near the center of the sample due to the non-uniform sintering process was confirmed.

In sample No. 106, which is a comparative example, the ratio of titanium hydride powder to the total mixed powder was 60 mass%, and a large amount of hydrogen was generated during the heating and sintering process, causing fine cracks to appear on the surface of the sintered body.

In addition, as the mixing ratio of titanium hydride powder in the mixed powder increases, i.e., 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. When titanium hydride powder is thermally decomposed during the sintering process, dissociated hydrogen atoms are generated, which react with the oxygen contained in the sample (hydrogen reduction action), resulting in a decrease in the oxygen content after sintering.

When we look at the amount of hydrogen remaining after sintering for samples No. 102 to 106, which were prepared so that the amount of titanium hydride powder was 10 to 60%, the value was 0.01 mass% or less, satisfying the JIS standard (H≦0.013 mass%).

The structure near the center of the sintered bodies of sample No. 101 (comparative example) and sample No. 104 (example) was observed using an optical microscope. The results are shown in Figure 8. Figure 8(a) shows the results for sample No. 101, and Figure 8(b) shows the results for sample No. 104. Figure 8 shows that the amount of voids in sample No. 104 (example) is smaller than that of sample No. 101 (comparative example), and that the density is increased.

[Test 3]

The low-hydrogen titanium powder is not limited to hydrogenated/dehydrogenated titanium powder, but may be titanium powder produced by, for example, an atomization method. Experiments were conducted using gas-atomized pure titanium powder as the starting material. The details are as follows.

Titanium hydride powder (average particle size: 48 μm, hydrogen content: 2.0-4.0% by mass) and gas-atomized pure titanium powder (average particle size: 27 μm, hydrogen content: 0.01-0.08% by mass) were used as starting materials, and the two powders were mixed in the ratio shown in Table 4.

100 g of each mixed powder was filled into a non-sealed rectangular mold with inner dimensions of 50 mm width x 70 mm length, and then the mold was placed in a vacuum heating furnace and heated and sintered under the heating and sintering pattern conditions shown below.

Heating and sintering pattern:

Room temperature → Heat to 650°C (hold for 1.5 hours) → Heat to 800°C (hold for 1.5 hours) → Heat to 1000°C (hold for 10 hours) → Cool inside the furnace → Remove the mold from the furnace at around 50°C.

Figure 9 shows the results of observing the mixed powder of sample No. 111 in Table 4 using a scanning electron microscope (SEM). The spherical powder indicated by the arrow is pure titanium powder produced by gas atomization. Although there is a difference in particle size, the two powders are mixed relatively uniformly.

The rectangular titanium sintered bodies obtained through the above heating and sintering patterns were subjected to analysis of density, relative density, oxygen content, nitrogen content, and hydrogen content, and to appearance observation. The density was measured using the Archimedes method, and the relative density (%) was calculated based on the specific gravity of pure Ti being 4.51 g/ ^cm3 . The results are shown in Table 4.

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, the sintering phenomenon did not progress sufficiently because the starting materials did not contain titanium hydride powder, and the target value for relative density (85% or more) was not met. In sample No. 112, which contains 60% titanium hydride powder in the starting materials, a large amount of hydrogen was generated, causing fine cracks to appear on the surface of the sintered body.

In addition, in samples No. 108 to 112, in which the amount of titanium hydride powder was adjusted to a mass ratio of 10% to 60%, the amount of hydrogen remaining in the sintered body was 0.009 mass% or less, satisfying the JIS standard (H≦0.013 mass%).

[Test 4]

The starting materials used were high-hydrogen titanium powder, which was prepared so that the hydrogen content in the titanium hydride powder was within the range of 0.8 to 1.5 mass%, and low-hydrogen titanium powder (pure titanium powder), in which the hydrogen content in the powder was unavoidably contained (0.01 to 0.08 mass%).

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

The starting powder, which had different ratios of titanium hydride powder and pure titanium powder, was filled into a non-sealed mold, and the starting powder was sintered in a vacuum atmosphere without applying pressure, using the following heating and sintering pattern.

Heating and sintering pattern:

Room temperature → (20℃/min) → 650℃ x 2h → (20℃/min) → 1000℃ x 10h → Furnace cooling

After sintering, the density, relative density, oxygen content, nitrogen content, and hydrogen content of the sintered body were measured, and the appearance of the sintered body was also observed. The results are shown in Table 6 below.

The hydrogen content in the prepared titanium hydride powder was 0.922 mass%, within the range of 0.8 to 1.5 mass%. Focusing on relative density, the relative density of the sintered bodies of samples No. 202 to 206, whose starting material powder had a hydrogen content in the range of 0.20 to 1.0 mass%, met the target value of 85% or more. The starting material powder for sample No. 206 was titanium hydride powder only, but because the hydrogen content in the starting material powder was 0.92 mass%, a sintered body with a relative density of 85% or more could be obtained by applying the powder packing sintering method using a non-sealed mold.

When we look at the amount of titanium hydride powder in the starting raw material powder, samples No. 202 to 206, which have a relative density of 85% or more, are those with a content of 20 to 100% by mass.

[Test 5]

The starting materials used were high-hydrogen titanium powder, which was prepared so that the hydrogen content in the titanium hydride powder was within the range of 0.8 to 1.5 mass%, and low-hydrogen titanium powder (pure titanium powder), in which the hydrogen content in the powder was unavoidably contained (0.01 to 0.08 mass%).

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

The starting powder, which had different ratios of titanium hydride powder and pure titanium powder, was filled into a non-sealed mold, and the starting powder was sintered in a vacuum atmosphere without applying pressure, using the following heating and sintering pattern.

Heating and sintering pattern:

Room temperature → (20℃/min) → 650℃ x 2h → (20℃/min) → 1000℃ x 10h → Furnace cooling

After sintering, the density, relative density, oxygen content, nitrogen content, and hydrogen content of the sintered body were measured, and the appearance of the sintered body was also observed. The results are shown in Table 8 below.

The hydrogen content of the prepared titanium hydride powder was 1.211% by mass, within the range of 0.8 to 1.5% by mass. Focusing on relative density, the relative density of the sintered bodies of samples No. 302 to 306, whose starting raw material powder had a hydrogen content of 0.25 to 1.21% by mass, met the target value of 85% or more. The starting raw material powder of sample No. 306 was titanium hydride powder only, but because the hydrogen content of the starting raw material powder was 1.21% by mass, a sintered body with a relative density of 85% or more could be obtained by applying the powder packing sintering method using a non-sealed mold.

When we look at the amount of titanium hydride powder in the starting raw material powder, samples No. 302 to 306, which have a relative density of 85% or more, are those with a content of 20 to 100% by mass.

[Experiment with different particle sizes of high hydrogen titanium powder]

The experiment was conducted under the same heating and sintering conditions as in Test 1, but with different particle sizes of the high-hydrogen titanium powder used.

The following three types of hydrogenated pure titanium powder were used for comparison:

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

b) Hydrogenated pure titanium powder with an average particle size of more than 10 μm and less than 45 μm (hydrogen content: 2.0 to 4.0% by mass)

c) Hydrogenated pure titanium powder with an average particle size of more than 45 μm and less than 150 μm (hydrogen content: 2.0 to 4.0% by mass)

Amount of hydrogenated pure titanium powder in the mixed powder: 40% by mass

The results are shown in Table 9 below.

The relative density of the sintered bodies of Sample No. 3 and Sample No. 7, in which the average particle size of the titanium hydride powder was 45 μm or less, was 92.5-94.6%. The tensile strength of Sample No. 3 after rolling was 798 MPa, and the breaking elongation was 30.0%. Sample No. 3 and Sample No. 7 can be used as practically effective titanium sintered materials.

The relative density of the sintered body of sample No. 8, in which the average particle size of the titanium hydride powder exceeds 45 μm, is 90.4%, which is higher than that of the sintered body of sample No. 1, which is made only of low-hydrogen titanium powder. However, the tensile strength and breaking elongation properties after rolling are inferior to those of sample No. 3 and sample No. 7, which use fine titanium hydride powder.

Based on the above results, if greater importance is placed on the tensile strength and breaking elongation properties after rolling, it seems desirable to use titanium hydride powder with an average particle size of 45 μm or less.

[Comparison with conventional manufacturing methods]

The mold powder filling sintering method of the present invention is characterized by the fact that no compression processing is performed on the starting raw material powder. For comparison, a compressed solidified body was produced by pressing using cold isostatic pressing (CIP), one of the conventional manufacturing methods, and then sintered. The size and heat treatment pattern of the sintered body were the same as those of the mold powder filling sintering method of the present invention in Test 1.

The powders used are as follows:

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

b) Dehydrogenated pure titanium powder with an average particle size of more than 10 μm and less than 45 μm

The results are shown in Table 10 below.

Focusing on sample No. 9 sintered after CIP molding, the amount of titanium hydride powder in the entire mixed powder is 40 mass%, which corresponds to sample No. 3 produced by the method of the present invention. Comparing sample No. 3 and sample No. 9, the density of the CIP molded 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 . It can be seen that the density of the sintered body is high even without pressing the packed powder in the method of the present invention because sintering is promoted by utilizing the high-speed diffusion of hydrogen dissociated by the decomposition of TiH2.

In terms of the blending ratio of the mixed powder, samples No. 10 and 11 correspond to samples No. 5 and 6 produced by the method of the present invention. The sintered bodies of samples No. 10 and 11, like samples No. 5 and 6, cracked during sintering.

The results in Table 10 show that the mold powder filling sintering method, which does not create a compressed solidified body, can produce sintered materials with properties equivalent to those of the conventional method, which creates a compressed solidified body by CIP molding and then sinters it. The present invention does not require a press machine, CIP equipment, or HIP equipment, so it is possible to achieve a significant reduction in equipment costs compared to the conventional method.

[Atmosphere during sintering process]

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

In the sintered body of sample No. 3 processed in a vacuum atmosphere, the amount of hydrogen in the sintered body composition was 0.005 mass %, and the relative density was 94.6%. The tensile strength after rolling was 798 MPa, and the breaking elongation was 30.0%.

In the case of the sintered body of sample No. 12, which was processed in an Ar gas atmosphere, a dehydrogenation treatment was performed for 50 hours after sintering in an Ar gas atmosphere. The amount of hydrogen in the composition of the final sintered body was 0.007 mass%, and the relative density was 92.5%. The tensile strength after rolling was 724 MPa, and the breaking elongation was 31.8%. In view of these characteristics, it is recognized that the titanium sintered material of sample No. 12, which was heated and sintered in an Ar gas atmosphere, can also be effectively used in practical applications.

The reason why good sintered density can be obtained even when heated and sintered in a non-vacuum atmosphere such as Ar gas is thought to be because, as shown in Figure 11, the hydrogen gas generated by the decomposition of TiH2 acts as a shield, suppressing the intrusion of oxygen into the titanium material.

[With or without mold lid]

The non-sealed type mold used in the mold powder filling sintering method of the present invention may be left open at the top (without a lid) or may have a lid on the top. We confirmed whether there was a significant difference in the properties of the sintered material after heating and sintering depending on whether or not there was a lid.

Two types of powders were prepared as starting materials: hydrogenated pure titanium powder and dehydrogenated pure titanium powder. In one mixed powder, the amount of hydrogenated pure titanium powder relative to the total mixed powder was adjusted to 20 mass%, and in the other mixed powder, the amount of hydrogenated pure titanium powder relative to the total mixed powder was adjusted to 50 mass%.

The two types of mixed powders were heated and sintered in a mold with and without a lid. The heating and sintering conditions were the same as for samples No. 1 to 6.

The results are shown in Table 12 below.

Focusing on samples No. 13 and No. 14, which have a ratio of hydrogenated pure titanium powder of 20% by mass, the relative density of the sintered body of sample No. 13, sintered in a mold with a lid, is 91.7%, while the relative density of the sintered body of sample No. 14, sintered in a mold without a lid, is 90.7. The difference in density is only 1%, and no significant difference is observed between the two.

Similarly, looking at samples No. 15 and No. 16, which have a 50% by mass ratio of hydrogenated pure titanium powder, the relative density of the sintered body of sample No. 15, sintered in a mold with a lid, is 95.6%, while the relative density of the sintered body of sample No. 16, sintered in a mold without a lid, is 92.0%. This difference is 3.6%, which is somewhat large, but a relative density of 92.0% is sufficiently high for practical purposes.

Figure 10 is a photograph showing the sintered body of sample No. 16 after sintering. As is clear from this photograph, there is a gap between the sintered body and the inner surface of the lidless mold, and it is recognized that the mixed powder used as the starting material has contracted in volume due to solid-phase sintering that utilizes the high-speed diffusivity of hydrogen.

[Sample containing titanium alloy powder as starting material]

Tests (Tests 6 and 7) were conducted to confirm that the mold powder filling sintering method using the non-sealed mold of the present invention can produce good sintered bodies even for samples that contain titanium alloy powder as a starting material.

[Test 6]

The starting materials used were two types: hydrogenated pure titanium powder and 64 titanium (Ti-6Al-4V) alloy powder. The mixture of these two types of powder was heated and sintered using a non-sealed mold with different compounding ratios. The heating and sintering conditions were the same as for samples No. 1 to 6. The results are shown in Table 13 below.

In Table 13, the relative densities of the filling powder and the sintered body were calculated based on the specific gravity of pure titanium being 4.51 g/ ^cm3 and the specific gravity of the titanium alloy being 4.43 g/ ^cm3 , and the calculated values based on the mixing ratio were used as the standard. The standard specific gravities are shown in Table 13 and Table 14 described later.

The relative density of the sintered body of sample No. 17, in which the amount of hydrogenated pure titanium powder relative to the total mixed powder was 20 mass%, was 90.0%. As already mentioned, sample No. 2 was a mixture of hydrogenated pure titanium powder and pure titanium powder, in which the amount of hydrogenated pure titanium powder relative to the total mixed powder was 20 mass%, and the relative density of the sintered body was 94.3%.

The relative density of the sintered body of sample No. 18, in which the amount of hydrogenated pure titanium powder relative to the entire mixed powder of hydrogenated pure titanium powder and 64 titanium alloy powder was 40 mass%, was 91.3%. The previously described sample No. 3, in which the amount of hydrogenated pure titanium powder relative to the entire mixed powder of hydrogenated pure titanium powder and pure titanium powder was 40 mass%, had a relative density of 94.6%.

For sample No. 19, in which the amount of hydrogenated pure titanium powder is 60% by mass relative to the total mixed powder of hydrogenated pure titanium powder and 64 titanium alloy powder, the relative density was not measured because the sample cracked during the sintering process, similar to the previously described sample No. 5 (a mixed powder of hydrogenated pure titanium powder and pure titanium powder, in which the amount of hydrogenated pure titanium powder is 60% by mass).

The test results for samples No. 17 to 19 confirmed that the mold powder packing sintering method using the non-sealed mold of the present invention is equally applicable to those using hydrogenated pure titanium powder and titanium alloy powder as starting materials, and that a sintered body with a high relative density can be obtained if the ratio of hydrogenated pure titanium powder is less than about 60%.

[Test 7]

The starting materials used were two types: hydrogenated titanium alloy (Ti-6Al-4V) powder and dehydrogenated pure titanium powder. The mixture of these two types of powder was heated and sintered in a non-sealed mold with different compounding ratios. The heating and sintering conditions were the same as for samples No. 1 to 6. The results are shown in Table 14 below.

The relative density of the sintered body of sample No. 20, in which the amount of hydrogenated titanium alloy powder is 20% by mass relative to the entire mixed powder of hydrogenated titanium alloy powder and pure titanium powder, is 92.7%. The amount of hydrogenated pure titanium powder in the previously mentioned sample No. 2, in which the amount of hydrogenated pure titanium powder is 20% by mass relative to the entire mixed powder of hydrogenated pure titanium powder and pure titanium powder, is 94.3%.

The relative density of the sintered body of sample No. 21, in which the amount of hydrogenated titanium alloy powder relative to the total mixed powder of hydrogenated titanium alloy powder and pure titanium powder is 40 mass%, is 90.2%. The amount of hydrogenated pure titanium powder relative to the total mixed powder of hydrogenated pure titanium powder and pure titanium powder of sample No. 3, as mentioned above, is 40 mass%, and the relative density of the sintered body is 94.6%.

The test results for samples No. 20 and 21 confirmed that the mold powder packing sintering method using the non-sealed mold of the present invention is equally applicable to those using hydrogenated titanium alloy powder and pure titanium powder as starting materials.

Tests 6 and 7 confirmed that the mold powder filling sintering method using the non-sealed mold of the present invention can produce good sintered bodies even for samples that contain titanium alloy powder as a starting material.

Although the embodiment of the present invention has been described above with reference to the drawings, the present invention is not limited to the embodiment described here, and various modifications are possible within the same or equivalent scope of the invention described in the claims.

The present invention can be advantageously used as a method for producing a titanium sintered material.

Claims (8)

preparing a high-hydrogen titanium powder containing a hydrogenated titanium compound as-treated and having a hydrogen content of 2.0 to 4.0 mass %;
preparing low-hydrogen titanium powder that has not been hydrogenated or has been hydrogenated and then dehydrogenated, and has a hydrogen content of 0.01 to 0.08 mass %;
a step of preparing a titanium-based starting raw material powder by mixing the high hydrogen titanium powder and the low hydrogen titanium powder so that the hydrogen content of the entire mixed powder is 0.2 to 2.0 mass %;
Filling the titanium-based starting material powder into a non-sealed mold;
and a step of heating and sintering the titanium-based starting material powder in the mold without applying pressure to obtain a titanium sintered material .
The heat sintering of the titanium-based starting material powder in the mold is performed by:
raising the temperature from room temperature to an intermediate temperature zone at which hydrogen in the titanium-based starting material powder is dissociated from titanium;
maintaining the titanium-based starting raw material powder in the intermediate temperature zone to dissociate hydrogen from titanium, and promoting sintering between powder particles by utilizing the high-speed diffusivity of the dissociated hydrogen;
raising the temperature of the titanium-based starting material powder from the intermediate temperature zone to a high temperature zone for sintering the titanium-based starting material powder;
maintaining the titanium-based starting material powder in the high temperature zone to complete sintering;
and cooling the sintered body after sintering from the high temperature zone 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 relative to the total amount of the mixed powder is 10 to 55 mass %. The hydrogen content in the high-hydrogen titanium powder is 0.8 to 1.5 mass %,
2. The method for producing a titanium sintered material according to claim 1 , wherein the amount of the high hydrogen titanium powder relative to the total amount of the mixed powder is 20 mass % or more but less than 100 mass %. The method for producing a titanium sintered material according to claim 1, wherein the titanium-based starting raw material powder is made of pure titanium that contains essentially only titanium as a metallic element. 2. 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. The intermediate temperature zone is in the range of 550°C to 850°C,
The method for producing a titanium sintered material according to claim 1 , wherein the high temperature zone is within a range of 850°C to 1400°C. The intermediate temperature zone has a low-temperature side intermediate temperature zone and a high-temperature side intermediate temperature zone,
2. The method for producing a titanium sintered material according to claim 1, wherein the titanium-based starting raw material powder is heated to the high-temperature side intermediate temperature zone after being held in the low-temperature side intermediate temperature zone, and heated to the high-temperature side intermediate temperature zone after being held in the high-temperature side intermediate temperature zone. 2. The method for producing a titanium-based sintered material according to claim 1 , wherein the titanium-based starting material powder in the mold is heated and sintered in a non-vacuum atmosphere.