JP2006104559A - Method for sintering titanium-based powder compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for sintering a titanium-based powder compact capable of producing a titanium-based sintered compact having reduced contamination caused by oxygen or the like even in an inert gas atmosphere and having satisfactory mechanical properties. <P>SOLUTION: A titanium-based powder compact 1 compacted from raw material powder essentially consisting of titanium is sintered by a heating furnace using a graphite heater in an inert gas atmosphere under the pressure of atmospheric pressure or higher, under an oxygen concentration of ≤50 ppm, and under a CO concentration of ≤100 ppm. At this time, the titanium-based powder compact 1 is supported by a supporting member 2 and is installed inside a case 3 made of graphite. The supporting member 2 is composed of a base part 20 and a reaction control part 21 comprising at least either Y<SB>2</SB>O<SB>3</SB>or ZrO<SB>2</SB>, and comes into contact with the titanium-based powder compact 1 via the reaction control part 21. Further, a sintering promotion member 5 made of titanium for forming a sintering promotion atmosphere is arranged around the titanium-based powder compact 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for sintering a titanium-based powder molded body that sinters a titanium-based powder molded body molded from a raw material powder containing titanium as a main component.

  Titanium is light, high in strength, and excellent in corrosion resistance. For this reason, it is used in various fields such as space / aviation equipment materials, biological / medical materials, and sports equipment. Moreover, since it has heat resistance and a superplastic function, it is expected as a structural material that can replace ferrous materials. A member made of an iron-based material is usually manufactured by a casting method or a forging method. However, an active metal such as titanium has many technical problems such as melting at a high temperature, and it is difficult to use a casting method or a forging method. Further, since titanium is a difficult-to-process material, it is difficult to manufacture a member by machining, and the processing cost is increased. For this reason, in the field | area where the cost restrictions, such as parts for motor vehicles, are large, the present condition is that the practical use of titanium is hard to advance.

Under such circumstances, a (near) net shape method using a powder metallurgy method has been attempted as a method for producing a member made of a titanium-based material. In the net shape method, first, a raw material powder containing titanium as a main component is pressure-molded to form a titanium-based powder molded body, and then the titanium-based powder molded body is sintered to form a sintered body. Here, the sintering of the titanium-based powder molded body is performed under a high vacuum of 10 ⁻² Pa or less in order to suppress deterioration of the mechanical properties of the sintered body due to oxygen contamination from the sintering atmosphere ( For example, see Patent Documents 1 to 3.) Sintering under high vacuum (hereinafter referred to as “vacuum sintering” as appropriate) requires evacuation of the heating furnace each time sintering is performed. Therefore, vacuum sintering is a batch process, which is inferior in mass productivity and high in cost. Also, in vacuum sintering, an expensive molybdenum (Mo) heater is often used as a heating source, which is also a factor of high cost.

Therefore, sintering in an inert gas atmosphere using an inexpensive graphite heater has been attempted. In the case of sintering in an inert gas atmosphere, contamination with oxygen, carbon, nitrogen, etc. from the inert gas and the furnace wall to be used becomes a problem more than in a high vacuum. As a countermeasure, for example, Patent Document 4 discloses a method of sintering a titanium-based powder compact by putting a getter metal that traps oxygen in a sintering case.
JP-A-3-267306 JP 2000-8102 A Japanese Patent Laid-Open No. 10-251706 JP-A-6-330105

  However, as disclosed in Patent Document 4, even if a getter metal is placed in the sintering case, contamination such as oxygen, carbon, and nitrogen cannot be sufficiently suppressed. For this reason, compared with the case of vacuum sintering, the mechanical characteristic of the obtained sintered compact becomes low.

  Recently, an extremely low oxygen partial pressure furnace capable of reducing the oxygen partial pressure in the furnace as much as possible has been developed. However, according to the inventor's experiment, even when this extremely low oxygen partial pressure furnace is used, absorption of a small amount of carbon, nitrogen, etc. into the sintered body is inevitable, and the mechanical properties of the sintered body, It turned out that ductility falls especially.

  In general, the titanium-based powder compact is installed in a sintering case supported by a support member. In this case, there has been a problem that the titanium-based powder molded body reacts with the support member during sintering to cause sticking. Due to the reaction between the titanium-based powder compact and the support member, oxygen, carbon, and the like derived from the support member enter the sintered body, and the mechanical properties of the sintered body deteriorate. In addition, distortion occurs in the sintered body, and the shape accuracy of the sintered body decreases.

  The present invention has been made in view of such a situation, and it is possible to produce a titanium-based sintered body having a good mechanical property with little contamination by oxygen, carbon, nitrogen, etc. even in an inert gas atmosphere. It is an object to provide a method for sintering a titanium-based powder compact.

(1) The first titanium-based powder molded body sintering method of the present invention (hereinafter referred to as “the first sintering method of the present invention” as appropriate) is molded from a raw material powder containing titanium as a main component. The titanium-based powder molded body is sintered in a heating furnace using a graphite heater, and the titanium-based powder molded body is supported by a support member. The support member comprises a base and a reaction suppression unit including at least one of Y ₂ O ₃ and ZrO ₂ , and is in contact with the titanium-based powder molded body through the reaction suppression unit, It is characterized by sintering in an inert gas atmosphere having an oxygen concentration of 50 ppm or less and a CO concentration of 100 ppm or less under a pressure of atmospheric pressure or higher.

In the first sintering method of the present invention, the titanium-based powder compact is supported by a support member and installed in the case. The support member includes a base portion and a reaction suppression portion, and comes into contact with the titanium-based powder molded body via the reaction suppression portion. Y ₂ O ₃ and ZrO ₂ constituting the reaction suppression part are stable at high temperatures and do not react with the titanium-based powder compact. Since the support member and the titanium-based powder molded body are in contact with each other with the reaction suppression portion interposed therebetween, the reaction between them does not occur. Therefore, the titanium powder compact and the support member do not stick. For this reason, the penetration | invasion of oxygen etc. from a support member to a titanium type powder compact is suppressed. Moreover, distortion of the obtained titanium-based sintered body is also suppressed. Therefore, according to the first sintering method of the present invention, a titanium-based sintered body having good mechanical characteristics and shape accuracy can be obtained.

  In the first sintering method of the present invention, sintering is performed in an inert gas atmosphere having an oxygen concentration of 50 ppm or less and a CO concentration of 100 ppm or less. That is, sintering is performed under conditions where the oxygen concentration and CO (carbon monoxide) concentration are extremely low. Therefore, there is little risk of oxygen and carbon contamination during sintering. In addition, since sintering is performed in an inert gas atmosphere, unlike vacuum sintering, there is no need for evacuation for each sintering. Therefore, according to the first sintering method of the present invention, sintering can be performed continuously.

  Thus, according to the first sintering method of the present invention, a titanium-based sintered body having good mechanical characteristics and shape accuracy can be mass-produced at low cost.

  (2) The second titanium powder molding method of the present invention (hereinafter referred to as “the second sintering method of the present invention” as appropriate) is formed from a raw material powder containing titanium as a main component. The titanium-based powder molded body is sintered in a heating furnace using a graphite heater, and the titanium-based powder molded body is placed in a graphite case. A titanium sintering promoting member for forming a sintering accelerating atmosphere is disposed around the green powder compact, and an inert gas atmosphere having an oxygen concentration of 50 ppm or less and a CO concentration of 100 ppm or less under a pressure of atmospheric pressure or higher. It is characterized by sintering.

  In the second sintering method of the present invention, a titanium sintering promoting member for forming a sintering promoting atmosphere is disposed around the titanium-based powder compact. Due to the arrangement of the sintering promoting member, the atmosphere around the titanium-based powder compact is promoted to sinter. Specifically, the sintering promoting member plays a role of isolating the atmosphere around the titanium-based powder molded body from the other atmosphere in the case. Further, since the sintering promoting member is made of titanium, it serves as a getter that captures oxygen, carbon, nitrogen, etc. present in the atmosphere during sintering. Thereby, the movement of oxygen, carbon, nitrogen and the like around the titanium-based powder compact is suppressed, and an atmosphere with higher cleanliness is realized around the titanium-based powder compact.

  Further, as the temperature rises, evaporation of titanium or the like occurs in the titanium-based powder compact. Usually, in an atmosphere at atmospheric pressure or higher, evaporation of titanium is less than in a vacuum atmosphere. This is thought to be because the evaporation and adhesion mechanism varies depending on the atmosphere. That is, in an atmosphere at atmospheric pressure or higher, contamination from the atmosphere has priority over titanium evaporation. For this reason, evaporation and adhesion of titanium are hindered, and sintering is hardly promoted. On the other hand, in the second sintering method of the present invention, the periphery of the titanium-based powder compact is maintained in a clean atmosphere with the sintering promoting member. As a result, evaporation and adhesion of titanium are promoted without being contaminated by oxygen or the like. It is considered that the evaporation of titanium occurs not only in the titanium-based powder molded body but also in the titanium sintering promoting member. Such an evaporation atmosphere of titanium also acts as a protective seal that prevents the movement of oxygen and the like. Sintering is promoted by repeated evaporation and adhesion of titanium. As a result, a titanium-based sintered body having the same level of ductility as vacuum sintering can be obtained.

  In the second sintering method of the present invention, as in the first sintering method of the present invention, sintering is performed in an inert gas atmosphere having extremely low oxygen and CO concentrations. For this reason, continuous sintering becomes possible, and deformation and deterioration of the sintering promoting member are small. Thus, according to the second sintering method of the present invention, a titanium-based sintered body having particularly high ductility can be mass-produced at a low cost.

(3) The third method for sintering a titanium-based powder molded body of the present invention (hereinafter referred to as “the third sintering method of the present invention” as appropriate) is formed from a raw material powder mainly composed of titanium. The titanium-based powder molded body is sintered in a heating furnace using a graphite heater, and the titanium-based powder molded body is supported by a support member. The support member comprises a base and a reaction suppression unit including at least one of Y ₂ O ₃ and ZrO ₂ , and is in contact with the titanium-based powder molded body through the reaction suppression unit, Around the titanium-based powder compact, a titanium-stimulating member for forming a sintering-promoting atmosphere is arranged, and an inert gas having an oxygen concentration of 50 ppm or less and a CO concentration of 100 ppm or less under a pressure higher than atmospheric pressure. It is characterized by sintering in a gas atmosphere.

  The third sintering method of the present invention is a method in which the first and second sintering methods of the present invention are combined. The support member comes into contact with the titanium-based powder molded body via the reaction suppression unit. For this reason, the reaction between the titanium-based powder molded body and the support member does not occur, and sticking of both is suppressed. As a result, intrusion of oxygen or the like from the support member into the titanium-based powder molded body and distortion of the obtained titanium-based sintered body are suppressed. Further, the sintering promoting member suppresses movement of oxygen, carbon, nitrogen and the like around the titanium-based powder molded body, and an atmosphere with higher cleanliness is realized around the titanium-based powder molded body. Thus, evaporation and adhesion of titanium are promoted without being contaminated by oxygen or the like. Sintering is further promoted by repeated evaporation and adhesion of titanium.

  Thus, according to the third sintering method of the present invention, it is possible to mass-produce a titanium-based sintered body having good mechanical properties such as ductility and good shape accuracy at a low cost.

  According to the method for sintering three titanium-based powder compacts of the present invention, titanium-based sintered bodies having good mechanical properties can be mass-produced at low cost. In particular, in the first sintering method of the present invention, reaction and sticking between the titanium-based powder compact and the support member are prevented. Thereby, the penetration | invasion of oxygen etc. from a support member to a titanium type powder compact and the distortion of the titanium type sintered compact obtained are suppressed. Further, in the second sintering method of the present invention, evaporation and adhesion of titanium are promoted while suppressing contamination of oxygen and the like. Thus, a titanium-based sintered body having a ductility equivalent to that of vacuum sintering can be obtained. Further, in the third sintering method of the present invention, the reaction and fixation between the titanium-based powder compact and the support member are prevented, and contamination with oxygen or the like is suppressed, and evaporation and adhesion of titanium are promoted. Thus, a titanium-based sintered body having high ductility and good shape accuracy can be obtained.

  Hereinafter, embodiments of the method for sintering three titanium powder compacts of the present invention will be described.

<First sintering method>
First, an embodiment of the first sintering method of the present invention will be described. FIG. 1 shows a cross-sectional view of a sintering case used in the first sintering method of the present invention. As shown in FIG. 1, a plate-like support member 2 is installed in a box-shaped case 3 opened upward. Case 3 is made of graphite. The support member 2 includes a graphite plate 20 and a sprayed layer 21 formed by spraying Y ₂ O ₃ on the surface thereof. The graphite plate 20 is included in the base of the support member that constitutes the present invention. Moreover, the thermal spray layer 21 is included in the reaction suppression part of the support member which comprises this invention. The titanium-based powder compact 1 is placed on the support member 2. The lower surface of the titanium-based powder compact 1 is in contact with the sprayed layer 21. The composition of the titanium-based powder molded body 1 is titanium (Ti) -6% aluminum (Al) -4% vanadium (V) (unit is mass%, the same applies hereinafter). Sintering is performed in a continuous sintering furnace (not shown) using a graphite heater while the case 3 containing the titanium-based powder compact 1 is moved in the furnace by a belt transport mechanism. The inside of the continuous sintering furnace is maintained in an argon (Ar) gas atmosphere having an atmospheric pressure, an oxygen concentration of 50 ppm or less, and a CO concentration of 100 ppm or less.

In the present embodiment, the titanium-based powder compact 1 is in contact with the sprayed layer 21 of the support member 2. The sprayed layer 21 is made of Y ₂ O ₃ that is stable at high temperatures and does not react with the titanium-based powder molded body 1. That is, the support member 2 and the titanium-based powder molded body 1 do not react with each other, and the sticking between them does not occur. For this reason, invasion of carbon and oxygen from the support member 2 to the titanium-based powder compact 1 and distortion of the obtained titanium-based sintered body are suppressed. In addition, since sintering is performed in an argon gas atmosphere with extremely low oxygen and CO concentrations, there is little risk of oxygen and carbon contamination. Moreover, since the continuous sintering furnace is used, the titanium-based sintered body can be mass-produced at a low cost.

  Next, another embodiment of the first sintering method of the present invention will be described. In the said embodiment, the titanium type powder compact of composition Ti-6% Al-4% V was used. However, the composition of the titanium-based powder compact is not limited to this. The titanium-based powder molded body may be any one formed from a raw material powder mainly composed of titanium. Here, “having titanium as a main component” means that the content ratio of titanium is 50 at% or more when the entire raw material powder is 100 at%. Examples of the raw material powder include pure titanium powder, titanium alloy powder, titanium compound powder, Al, V, iron (Fe), Mo, tin (Sn), niobium (Nb), silicon (Si), manganese (Mn ), Zirconium (Zr), tantalum (Ta), boron (B), or the like, or a powder of an alloy containing the same element can be used. The raw material powder may be one type of powder or a mixture of two or more types of powder.

  The raw material powder may be pressure-molded by a known method to form a titanium-based powder compact. For example, when a raw material powder is filled in a mold having an inner surface coated with a higher fatty acid-based lubricant and pressed at a pressure of 392 MPa or more in a warm state at 100 to 225 ° C., a high-density titanium-based powder molded body Can be obtained. The higher the density of the titanium-based powder compact, the smaller the dimensional change before and after sintering. As a result, the net shape can be realized, and the price of titanium products can be reduced.

In the above embodiment, the reaction suppress part of the support member and the sprayed layer of Y ₂ O _3. The reaction suppression unit may include at least one of Y ₂ O ₃ and ZrO ₂ . For example, there is a mode including both of Y ₂ O _3, ZrO ₂ in any embodiments composed of one or Y ₂ O ₃ and ZrO _2,. Also, other oxides (CaO, Al ₂ O _3, etc.) may be contained. However, when sintering is performed at a high temperature, it is necessary to consider the decomposition of the oxide. For example, Al ₂ O ₃ is decomposed in a sintering atmosphere having a temperature of 1300 ° C. or higher and a CO concentration of 10 ppm or lower. CaO is hygroscopic and difficult to handle. In contrast, Y ₂ O ₃ is suitable because it is stable in any atmosphere at a high temperature of 1300 ° C. or higher.

As the reaction suppressing portion, various modes such as a sintered plate disposed on the surface of the base portion and powder laid on the surface of the base portion can be adopted in addition to the sprayed layer. In consideration of cost, surface flatness, etc., it is desirable to adopt the form of the sprayed layer. The thermal spray layer may be formed by spraying a thermal spray material containing at least one of Y ₂ O ₃ and ZrO _{2 on} the surface of the base by plasma spraying, gas spraying, or the like. In this case, the thickness of the sprayed layer is preferably 100 μm or less. When it is thicker than 100 μm, the sprayed layer is easily peeled off from the base.

  Further, when the reaction suppression portion is a sprayed layer, it is desirable to provide an intermediate layer on the base portion in order to improve the adhesion between the base portion and the sprayed layer. That is, it is desirable that the base is composed of a base body and an intermediate layer, and a sprayed layer is formed on the surface of the intermediate layer. In this case, the support member has a configuration of “base body / intermediate layer / sprayed layer”. For example, when the base body is made of graphite, the intermediate layer may be made of a metal having a high melting point and a thermal expansion coefficient similar to that of carbon. Examples of such metals include Mo, tungsten (W), Ta, and the like. One or more of these metals may be sprayed onto the base body to form the intermediate layer. A plurality of intermediate layers may be formed. The thickness of the intermediate layer is preferably 10 μm or more and 100 μm or less, for example.

  In the said embodiment, the titanium type powder compact was mounted on the plate-shaped support member. However, various types of support members can be employed depending on the shape of the titanium-based powder compact. In any case, the titanium-based powder molded body and the support member may be brought into contact with each other via the reaction suppression unit. Moreover, in the said embodiment, the continuous sintering furnace provided with the belt conveyance mechanism was used from a viewpoint of mass productivity and cost. However, a batch-type heating furnace may be used.

  The sintering temperature and sintering time may be determined in consideration of desired characteristics of the titanium-based sintered body, productivity, and the like. As the sintering temperature is higher, a high-strength titanium-based sintered body can be obtained in a shorter time. However, if the sintering temperature is too high, the titanium-based powder molded body and the support member may react even in a state where the reaction suppressing portion is interposed. On the other hand, if the sintering temperature is too low, element diffusion becomes insufficient, which is not preferable. In addition, the sintering time becomes longer and the productivity is lowered. Therefore, the sintering temperature is preferably 1000 ° C. or higher and 1500 ° C. or lower. It is more preferable that the temperature is 1100 ° C. or higher and 1300 ° C. or lower. The sintering time is preferably about 0.5 to 4 hours, although it depends on the sintering temperature.

<Second sintering method>
First, an embodiment of the second sintering method of the present invention will be described. FIG. 2 shows a sectional view of a sintering case used in the second sintering method of the present invention. 2, parts corresponding to those in FIG. 1 are denoted by the same reference numerals as in FIG. This embodiment differs from the above-described embodiment of the first sintering method of the present invention only in the form of the support member and the sintering promoting member. Therefore, the difference will be mainly described here.

  As shown in FIG. 2, a plate-like support 4 is installed in a box-shaped case 3 opened upward. Both the case 3 and the support base 4 are made of graphite. The titanium-based powder compact 1 is placed on the support 4. The composition of the titanium-based powder compact 1 is Ti-6% Al-4% V. The titanium-based powder compact 1 is surrounded by a titanium cover 5. The cover 5 has a box shape opened downward. Vents 50 a and 50 b that vent the inside and outside of the cover 5 are provided at the lower ends of both walls of the cover 5. The cover 5 is included in the sintering promoting member in the present invention. Sintering is performed in a continuous sintering furnace (not shown) using a graphite heater while the case 3 containing the titanium-based powder compact 1 is moved in the furnace by a belt transport mechanism. The inside of the continuous sintering furnace is maintained in an argon gas atmosphere having an atmospheric pressure, an oxygen concentration of 50 ppm or less, and a CO concentration of 100 ppm or less.

The behavior during sintering will be described with reference to FIGS. 3 and 4. FIG. 3 shows the behavior of the temperature raising process (from 400 ° C.), and FIG. 4 shows the behavior of the sintering process (from 1000 ° C.). As shown in FIG. 3, by surrounding the titanium-based powder compact 1 with a cover 5, the periphery of the titanium-based powder compact 1 is isolated from the atmosphere outside the cover 5. Thereby, the movement of oxygen (O ₂ ), CO, and nitrogen (N ₂ ) around the titanium-based powder compact 1 is suppressed. In the temperature raising process, hydrogen (H ₂ ) contained in the titanium-based powder compact 1 is released. As a result, the hydrogen pressure in the cover 5 is increased, and the intrusion of O ₂ , CO, and N ₂ into the cover 5 is further suppressed. Here, since the vent holes 50a and 50b are provided at the lower ends of both walls of the cover 5, they are effective in suppressing the intrusion of a gas heavier than hydrogen. Thus, an atmosphere with a high cleanliness is formed around the titanium-based powder compact 1.

  When the temperature rises further and the sintering process is started, titanium is evaporated in the titanium-based powder compact 1 as shown in FIG. Since the surroundings of the titanium-based powder molded body 1 have an atmosphere with a high cleanliness, evaporation and adhesion of titanium are promoted. The evaporation of titanium occurs not only in the titanium-based powder compact 1 but also in the cover 5. This titanium evaporation atmosphere prevents C, O, and N from entering the cover 5. Furthermore, the cover 5 captures C, O, N, and H. As a result, a clean atmosphere is maintained inside the cover 5 and sintering is promoted by evaporation and adhesion of titanium. Thereby, a titanium-based sintered body having a ductility equivalent to that of vacuum sintering can be obtained. Further, since the oxygen concentration and the CO concentration during sintering are extremely low, the deterioration of the cover 5 is small.

  Next, another embodiment of the second sintering method of the present invention will be described. In the above embodiment, the box-shaped cover 5 is used as the sintering promoting member. As long as the sintering promoting member can form a sintering promoting atmosphere around the titanium-based powder compact 1, the shape, the arrangement, and the like are not particularly limited. For example, the sintering promoting member may not cover the entire titanium-based powder molded body 1. Moreover, what is necessary is just to use what manufactured the titanium rolling plate by plastic processing, what shape | molded titanium powder in the predetermined shape, what sintered it, etc. as a sintering promotion member. The sintering promoting member gradually deteriorates during the sintering process due to capture of C, O, N, and the like. That is, the sintering promoting member that has undergone sintering includes TiC, TiN, and the like in addition to Ti. For this reason, in the present specification, the term “made of titanium” is used, including not only pure titanium but also a deteriorated form thereof.

  In the above embodiment, the vent holes 50 a and 50 b are provided at the lower ends of both walls of the cover 5. However, the position and number of the vents are not particularly limited. What is necessary is just to provide suitably according to the shape of the cover surrounding a titanium-type powder compact.

  The titanium-based powder compact 1 usually contains hydrogen which is unavoidable for the production of titanium powder. However, when it is desired to further promote the release of hydrogen, a titanium-based powder compact may be formed using a hydride powder such as titanium hydride. The composition of the titanium-based powder compact, the molding method, the heating furnace to be used, the sintering temperature, and the sintering time are in accordance with the first sintering method of the present invention.

<Third sintering method>
One embodiment of the third sintering method of the present invention will be described. FIG. 5 shows a sectional view of a sintering case used in the third sintering method of the present invention. 5, parts corresponding to those in FIGS. 1 and 2 are denoted by the same reference numerals as those in FIGS. This embodiment corresponds to a combination of the above two embodiments.

As shown in FIG. 5, a plate-like support member 2 is installed in a box-shaped case 3 opened upward. Case 3 is made of graphite. The support member 2 includes a graphite plate 20 and a sprayed layer 21 formed by spraying Y ₂ O ₃ on the surface thereof. The graphite plate 20 is included in the base of the support member that constitutes the present invention. Moreover, the thermal spray layer 21 is included in the reaction suppression part of the support member which comprises this invention. The titanium-based powder compact 1 is placed on the support member 2. The lower surface of the titanium-based powder compact 1 is in contact with the sprayed layer 21. The composition of the titanium-based powder compact 1 is Ti-6% Al-4% V.

  The titanium-based powder compact 1 is surrounded by a titanium cover 5. The cover 5 has a box shape opened downward. Vents 50 a and 50 b that vent the inside and outside of the cover 5 are provided at the lower ends of both walls of the cover 5. The cover 5 is included in the sintering promoting member in the present invention.

  Sintering is performed in a continuous sintering furnace (not shown) using a graphite heater while the case 3 containing the titanium-based powder compact 1 is moved in the furnace by a belt transport mechanism. The inside of the continuous sintering furnace is maintained in an argon gas atmosphere having an atmospheric pressure, an oxygen concentration of 50 ppm or less, and a CO concentration of 100 ppm or less.

In the present embodiment, the titanium-based powder compact 1 is in contact with the sprayed layer 21 of the support member 2. The sprayed layer 21 is made of Y ₂ O ₃ that is stable at high temperatures and does not react with the titanium-based powder molded body 1. That is, the support member 2 and the titanium-based powder molded body 1 do not react with each other, and the two do not stick together. For this reason, invasion of carbon and oxygen from the support member 2 to the titanium-based powder molded body 1 and distortion of the obtained titanium-based sintered body are suppressed. In addition, since sintering is performed in an argon gas atmosphere with extremely low oxygen and CO concentrations, there is little risk of oxygen and carbon contamination. Furthermore, a high clean atmosphere is formed by the cover 5 around the titanium-based powder compact 1. For this reason, in the titanium-based powder molded body 1, evaporation and adhesion of titanium are promoted. Thus, according to the present embodiment, a titanium-based sintered body having good mechanical properties such as ductility and good shape accuracy can be mass-produced at a low cost.

  As another embodiment of the third sintering method of the present invention, the composition of the titanium-based powder compact, the molding method, the support member, the sintering promoting member, the heating furnace to be used, the sintering temperature, and the sintering time are as follows. All conform to the first and second sintering methods of the present invention.

  Based on the said embodiment, the titanium type powder compact was sintered. Elemental analysis of the obtained titanium-based sintered body was conducted to investigate the degree of contamination and to evaluate mechanical properties. Moreover, about the support member used in the case of sintering, durability of the reaction suppression part by the difference in a structure was investigated. Hereinafter, forming and sintering of a titanium-based powder molded body, elemental analysis of the titanium-based sintered body, evaluation of mechanical characteristics, and durability of the reaction suppressing unit will be described in order.

(1) Molding of titanium-based powder molded body A titanium-based powder molded body having the composition Ti-6% Al-4% V was molded. First, pure titanium powder (average particle size 80 μm) and Al ₃ V powder (average particle size 7 μm) were mixed to prepare a raw material powder. Next, the prepared raw material powder was put in a dryer and heated to 150 ° C. in an air atmosphere. For molding, a mold having a cylindrical cavity (φ23 mm × 50 mm) was used. This mold was heated to 150 ° C. in the atmosphere. A 1.2% lithium stearate aqueous solution of a lubricant was applied to the inner surface of the heated mold with a spray gun. This mold was filled with heated raw material powder, and warm press molding was performed at a pressure of 294 to 1960 MPa.

(2) Sintering of titanium-based powder compact (I) The obtained titanium-based powder compact is placed in the case in the embodiment shown in FIG. 5 (third sintering method of the present invention), Sintering was performed in a continuous sintering furnace (manufactured by Kanto Metallurgical Co., Ltd., oxynon furnace) equipped with a graphite heater. Sintering was performed in an argon gas atmosphere with an oxygen concentration of 50 ppm or less and a CO concentration of 100 ppm or less under atmospheric pressure. Hereinafter, this sintering atmosphere is referred to as “very low oxygen atmosphere”. The furnace temperature was maintained at 1000 to 1500 ° C., and the case containing the titanium-based powder compact was moved so that the time for maintaining the desired temperature was 0.5 to 4 hours.

  (II) For comparison, the same titanium-based powder molded body as described above was used, and sintering was performed in the following various modes.

(A) Conventional vacuum sintering A high-temperature vacuum heating furnace (manufactured by Nemus, FD-25) was used for sintering. The heating source of the furnace is a Mo heater, and the case where the titanium-based powder compact is disposed is made of W. Sintering was performed in a vacuum atmosphere of 10 ⁻³ Pa at a temperature of 1100 ° C. or 1200 ° C. for 0.5 hours.

(B) Sintering in Conventional Argon Gas Atmosphere For the sintering, a Shimadzu pressure sintering rapid cooling furnace (manufactured by Shimadzu Corporation, PVSGgr 20/20) was used. The heating source of the furnace is a graphite heater, and the case where the titanium-based powder compact is disposed is also made of graphite. Sintering was carried out at atmospheric pressure under a 99.995% argon gas atmosphere at a temperature of 1100 ° C. or 1200 ° C. for 0.5 hours. Note that the oxygen concentration and CO concentration in the argon gas atmosphere were not managed.

(C) Sintering with Mo Cover In the sintering method (I) (the embodiment shown in FIG. 5), the cover material was changed to Mo. Other than that, it sintered similarly to said (I).

(D) Sintering Using Titanium Getter In the sintering method (I) (the embodiment shown in FIG. 5), a titanium getter was placed in the case in place of the titanium cover. The getters were pure titanium powder compacts (φ10 mm × 40 mm), and six were arranged around the titanium-based powder compacts. Other than that, it sintered similarly to said (I).

(E) Sintering without Cover In the sintering method (I) (the embodiment shown in FIG. 5), sintering was performed without using a titanium cover. That is, this mode corresponds to the first sintering method of the present invention (the mode shown in FIG. 1).

(3) Elemental analysis of titanium-based sintered body Elemental analysis was performed on titanium-based sintered bodies obtained by various sintering methods. The results are shown in Table 1. Table 1 also shows the results for the raw material powder.

  As shown in Table 1, in the sintered body [(I), (II) -e] sintered in an extremely low oxygen atmosphere, the sintered body [(II) -b] sintered in a conventional argon gas atmosphere The content of O, C, and N was small as compared with. From this, it can be seen that when sintered in an extremely low oxygen atmosphere, there is little contamination with impurity elements. In particular, when a titanium cover was used [(I)], there was little contamination of C and N. In addition, the surface of the sintered body [(II) -b] sintered in the conventional argon gas atmosphere was altered by absorption of the impurity element, and expanded and deformed unevenly.

  In addition, the titanium cover used in the sintering method (I) was subjected to elemental analysis, and the components before and after sintering were compared. The results are shown in Table 2.

  As shown in Table 2, all elements increased after sintering. From this, it can be seen that the titanium cover captures O, H, C, and N. However, since sintering was performed in an extremely low oxygen atmosphere, the amount of increase of these elements is not so large. From this result, it can be seen that the sintering in the extremely low oxygen atmosphere causes little deterioration of the titanium cover, and the cover can be used repeatedly.

(4) Evaluation of mechanical properties of titanium-based sintered body Titanium-based sintered bodies obtained by various sintering methods were processed into test pieces for tensile tests, and tensile tests were performed on the respective test pieces. The tensile test method was in accordance with JIS Z 2241. As a result of the tensile test, FIG. 6 shows the value of the elongation at break of each test piece at room temperature. As shown in FIG. 6, the sintered body [(I)] sintered using the titanium cover exhibited the same level of elongation as the sintered body [(II) -a] sintered in vacuum. On the other hand, the elongation of the sintered body [(II) -b] sintered in the conventional argon gas atmosphere is small. In particular, when sintered at 1200 ° C., the surface of the titanium-based sintered body is contaminated with C. Measurement was not possible due to deformation. Also, a sintered body [(II) -c] sintered using a Mo cover, a sintered body [(II) -d] sintered using a titanium getter, and sintered without a cover. In the sintered body [(II) -e], the contamination by the impurity element is small, but the elongation is lower than that in the vacuum sintering.

  FIG. 7 shows the relationship between the sintering temperature and the elongation at break. FIG. 7 shows a comparison between a sintered body [(I)] sintered using a titanium cover and a sintered body [(II) -e] sintered without a titanium cover. As shown in FIG. 7, the elongation was greater when the titanium cover was used at all sintering temperatures. This is because evaporation and adhesion of titanium were promoted by maintaining a clean atmosphere inside the cover. In addition, the elongation increased as the sintering temperature increased regardless of the presence or absence of the cover. This is because the higher the temperature, the more the evaporation of Ti, Al, and V is promoted, the element diffusibility is increased, and the sintering is promoted.

(5) Durability of reaction suppressing portion in support member Various support members having different configurations were produced. A sintering test was performed using the prepared support member, and the durability of the reaction suppression portion was investigated. The sintering test was performed according to the first sintering method of the present invention (the embodiment shown in FIG. 1). Table 3 shows the structure of the produced support member and the evaluation of the reaction suppression portion with respect to the sintering temperature.

As shown in Table 3, when the Y ₂ O ₃ powder is laid and used as a reaction suppression portion, the reaction with the sintered body is suppressed, but the lower surface of the sintered body in contact with the Y ₂ O ₃ powder In addition, the Y ₂ O ₃ powder was caught. In FIG. 8, the optical microscope photograph of the upper surface and lower surface of the sintered compact sintered at 1300 degreeC is shown. As can be seen from the photograph in FIG. 8, Y ₂ O ₃ powder adheres to the lower surface of the sintered body.

In addition, when the Y ₂ O ₃ sintered plate was used as the reaction suppressing portion, no change was observed on any contact surface of the Y ₂ O ₃ sintered plate and the sintered body even when the sintering was repeated. . FIG. 9 shows optical micrographs of the non-contact surface and the contact surface of the Y ₂ O ₃ sintered plate and the non-contact surface and the contact surface of the sintered body when sintered at 1400 ° C. No adhesion of Y ₂ O ₃ is observed on the contact surface of the sintered body.

Further, in the case where the sprayed layer sprayed with Y ₂ O ₃ or the like was used as the reaction suppressing portion, when the sintering was repeated, the sprayed layer was slightly peeled off. FIG. 10 shows optical micrographs of the non-contact surface and the contact surface of the Y ₂ O ₃ sprayed layer and the non-contact surface and the contact surface of the sintered body when sintered at 1400 ° C. A little Y ₂ O ₃ is adhered to the lower surface (contact surface) of the sintered body in contact with the Y ₂ O ₃ sprayed layer.

Further, in an aspect in which an intermediate layer such as a Mo layer is provided at the base of the support member and a sprayed layer such as Y ₂ O ₃ is formed on the surface of the intermediate layer, either the sprayed layer or the sintered body can be used even if sintering is repeated. There was no change in the contact surface. FIG. 11 shows optical microscope photographs of the non-contact surface and the contact surface of the Y ₂ O ₃ sprayed layer / Mo intermediate layer and the non-contact surface and the contact surface of the sintered body after being sintered 10 times at 800 to 1300 ° C. Indicates. FIG. 12 shows an optical micrograph of the contact surface of the Y ₂ O ₃ sprayed layer / W intermediate layer and the contact surface of the sintered body when sintered at 1400 ° C. 11 and 12, no Y ₂ O ₃ adheres to the contact surface of the sintered body.

From the above results, it was found that the Y ₂ O ₃ sintered plate is excellent in durability and suitable as a reaction suppressing part. However, in the case of a Y ₂ O ₃ sintered plate, the manufacturing cost increases and the degree of freedom in shape is limited. Considering this point, a sprayed layer in which Y ₂ O ₃ or the like is sprayed is suitable for the reaction suppressing portion. In particular, when an intermediate layer made of Mo, W or the like is provided on the base and a sprayed layer is formed thereon, the adhesion of the sprayed layer is improved and the durability is further improved.

  According to the method for sintering a titanium-based powder molded body of the present invention, a lightweight and high-strength titanium-based member can be mass-produced. For this reason, it becomes possible to substitute various mass-produced parts such as automobile parts, sporting goods, and tools from conventional steel products to titanium alloy products.

It is sectional drawing of the case for sintering used with the 1st sintering method of this invention. It is sectional drawing of the case for sintering used with the 2nd sintering method of this invention. The behavior of the temperature rising process (from 400 ° C.) during sintering is shown. The behavior of the sintering process (from 1000 ° C.) during sintering is shown. It is sectional drawing of the case for sintering used with the 3rd sintering method of this invention. It is a graph which shows the elongation at break of each test piece at room temperature. It is a graph which shows the relationship between the sintering temperature by the difference in a sintering method, and breaking elongation. It is an optical microscope photograph of the upper and lower surfaces of the sintered body (Y ₂ O ₃ powder laying). Non-contact surface and the contact surface of the Y ₂ O ₃ sintered plate, and an optical micrograph of the non-contact surface and the contact surface of the sintered body. Non-contact surface and the contact surface of the Y ₂ O ₃ sprayed layer, and an optical micrograph of the non-contact surface and the contact surface of the sintered body. Non-contact surface and the contact surface of the Y ₂ O ₃ sprayed layer / Mo intermediate layer, and an optical micrograph of the non-contact surface and the contact surface of the sintered body. The contact surface of the Y ₂ O ₃ sprayed layer / W intermediate layer, and an optical micrograph of the contact surface of the sintered body.

Explanation of symbols

1: Titanium-based powder compact 2: Support member 20: Graphite plate (base part) 21: Thermal spray layer (reaction suppression part)
3: Case 4: Support base 5: Cover (sintering promotion member) 50a, 50b: Vent

Claims (6)

A method for sintering a titanium-based powder molded body in which a titanium-based powder molded body molded from a raw material powder mainly composed of titanium is sintered in a heating furnace using a graphite heater,
The titanium-based powder compact is supported by a support member and installed in a graphite case.
The support member includes a base and a reaction suppression unit including at least one of Y ₂ O ₃ and ZrO ₂ , and is in contact with the titanium-based powder molded body through the reaction suppression unit,
A sintering method for a titanium-based powder compact characterized by sintering in an inert gas atmosphere having an oxygen concentration of 50 ppm or less and a CO concentration of 100 ppm or less under a pressure of atmospheric pressure or higher.   2. The method for sintering a titanium-based powder molded body according to claim 1, wherein the reaction suppression unit is a sprayed layer formed on the surface of the base or a sintered plate disposed on the surface of the base. The base comprises a base body and an intermediate layer,
The method for sintering a titanium-based powder molded body according to claim 1, wherein the reaction suppression unit is a sprayed layer formed on a surface of the intermediate layer. A method for sintering a titanium-based powder molded body in which a titanium-based powder molded body molded from a raw material powder mainly composed of titanium is sintered in a heating furnace using a graphite heater,
Installing the titanium-based powder compact in a graphite case,
Around the titanium-based powder compact, a titanium-sintering promoting member for forming a sintering-promoting atmosphere is disposed,
A sintering method for a titanium-based powder compact characterized by sintering in an inert gas atmosphere having an oxygen concentration of 50 ppm or less and a CO concentration of 100 ppm or less under a pressure of atmospheric pressure or higher. The sintering promoting member is a cover that surrounds the titanium-based powder molded body,
The method for sintering a titanium-based powder molded body according to claim 4, wherein the cover has an air vent for ventilating the inside and outside of the cover. A method for sintering a titanium-based powder molded body in which a titanium-based powder molded body molded from a raw material powder mainly composed of titanium is sintered in a heating furnace using a graphite heater,
The titanium-based powder compact is supported by a support member and installed in a graphite case.
The support member includes a base and a reaction suppression unit including at least one of Y ₂ O ₃ and ZrO ₂ , and is in contact with the titanium-based powder molded body through the reaction suppression unit,
Around the titanium-based powder compact, a titanium-sintering promoting member for forming a sintering-promoting atmosphere is disposed,
A sintering method for a titanium-based powder compact characterized by sintering in an inert gas atmosphere having an oxygen concentration of 50 ppm or less and a CO concentration of 100 ppm or less under a pressure of atmospheric pressure or higher.

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