JP2004176125A - Die material superior in mold releasing property in electrification sintering, and compacted member using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a compacted member with high precision by improving a die releasing property in electrification sintering, and to provide the compacted member. <P>SOLUTION: This method for producing a compact using an electroconductive ceramic containing zirconium oxide in a contacting part with the compact, in electrification sintering, and a material having different electrical characteristics from those of the ceramic between the ceramic and an electrode, to prevent destruction of a die caused by a thermal shock and copy a surface fine form of the die onto the compact with high precision by a high applied pressure. The compact can be easily separated from the die without using a mold releasing material, but by using a phenomenon that oxygen in zirconium oxide is migrated by the electrification and is released from the die. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a mold material excellent in releasability that enables to produce a high-precision molded member in electric current sintering, and a molded member produced using the same.More specifically, the present invention relates to zirconium oxide. Using the conductive ceramic material contained in the mold material, the transfer of oxygen of zirconium oxide from the inside of the mold to the surface of the mold causes high-precision shape formation with improved mold releasability during electrical sintering. The present invention relates to a mold material that can be used, a method for manufacturing a molded member using the same, and a molded member.
Since the compact produced by the electric sintering according to the present invention has a higher processing accuracy than the conventional electric sinter, and has excellent releasability from a mold, the method of the present invention employs, for example, near net shape molding. It is useful as a method for molding difficult-to-process materials such as intermetallic compounds, high-hardness materials that are difficult to finish, and minute members.
[0002]
[Prior art]
BACKGROUND ART Conventionally, graphite has been generally used as a mold material in electric current sintering because it has conductivity, has excellent strength at high temperatures, and has excellent workability. In addition, when conducting electric sintering using a large pressure, a mold material made of cemented carbide is used for low-temperature molding, and high-strength using conductive ceramics such as SiC for high-temperature molding. (Made of black ceramic) has been used.
[0003]
In the case of electric sintering, the electrode portion is water-cooled, and a large temperature difference occurs between the electrode and the molding die during energization. For example, current sintering of titanium powder requires heating at 800 ° C. or more, and a temperature difference of 500 ° C. or more occurs between the electrode and the mold. Therefore, it is necessary to select a material that is not easily cracked by a thermal shock (stress generated by a temperature difference) as the mold material, and there is naturally a limitation on available mold materials. For this purpose, for example, graphite, cemented carbide, and the like have been used as mold materials for electric current sintering (for example, see Patent Documents 1-2 and Non-Patent Documents 1-2).
[0004]
However, the graphite mold has a problem that it easily reacts with the metal, and it is difficult to produce a highly accurate molded body. In addition, there is a possibility that the cemented carbide mold may be deformed (buckled) at a temperature of 600 ° C. or higher, and it is difficult to obtain a highly accurate molded body. Therefore, some prior arts of a mold in spark sintering have been proposed (for example, see Patent Documents 3 to 7). However, in electric current sintering, for example, non-conductive oxide ceramics, In fact, the use of densified ceramics having poor thermal shock properties as mold materials for molding has not been studied much.
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2001-220247 [Patent Document 2]
JP-A-9-53103 [Patent Document 3]
JP 2000-239709 A [Patent Document 4]
JP-A-7-330446 [Patent Document 5]
JP 2001-220247 A [Patent Document 6]
JP 2001-226703 A [Patent Document 7]
JP 2001-253779 A [Non-Patent Document 1]
Masao Tokita Journal of the Society of Powder Technology, 30 (1993), 790
[Non-patent document 2]
H. Yanagisawa, H. Akiyama, and K. Matsuki: Materia (Journal of the Japan Institute of Metals), 33 (1994), 1489.
[Non-Patent Document 3]
Keizo Kobayashi: Science and Industry, 74 (5), 221 (2000)
[0006]
[Problems to be solved by the invention]
Under these circumstances, the present inventors have conducted intensive studies in view of the above-mentioned prior art in order to drastically solve the various problems in the above-mentioned prior art. The inclusion of zirconium oxide in the zirconium oxide and the discovery that there is a transfer phenomenon of oxygen in the zirconium oxide corresponding to the flow of electricity, and the formation of a gap between the molded body and the oxygen when it escapes from the mold. And completed the present invention.
That is, in the present invention, in the current-carrying sintering, by causing zirconium oxide to be contained in the conductive ceramic of the mold material, the movement of oxygen in the zirconium oxide in accordance with the flow of electricity is caused, so that the molded body and the mold are formed. It is an object of the present invention to provide a mold material capable of giving a high-precision shape with improved mold releasability, a method for producing a molded body using the same, and a molded member.
[0007]
[Means for Solving the Problems]
The present invention for solving the above-mentioned problems includes the following technical means.
(1) A mold material excellent in releasability used when producing a molded body by sintering a molding material while energizing, and a conductive ceramic containing zirconium oxide in a portion in contact with the molded body High mold release type material characterized by using.
(2) The mold material according to the above (1), which is a mold material used when sintering by direct current.
(3) A method for producing a molded member using the mold material according to the above (1) or (2), wherein the molded material is sintered while being energized to produce a molded body. As a material, a conductive ceramic containing zirconium oxide is used in the part in contact with the molded body, and electricity is passed between the electrodes to move oxygen of zirconium oxide from the inside of the mold to the surface of the mold, and a gas flows between the mold and the molded body. , And releasing the molded body by utilizing the pressure of the gas generated from the mold.
(4) The method according to (3), wherein a material having a different electric resistance from the ceramic is used between the conductive ceramic and the electrode.
(5) The method according to (3), wherein the sintering is performed by a direct current.
(6) The method according to the above (3), wherein a conductive ceramic containing zirconium oxide in a part in contact with the molded body is used.
(7) A material to be molded and another substance are put into a mold, and the material to be molded is formed into a molded body, and the molded body is joined to another substance by using the pressure of gas generated from the mold to form a composite. The method according to (3) above.
(8) A molded member produced by the method according to any one of (3) to (7), wherein a fine surface shape of a mold is transferred with high accuracy.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described in more detail.
The present invention provides a conductive ceramic containing zirconium oxide, utilizing the transfer of oxygen of zirconium oxide in accordance with the flow of electricity during energization, preventing adhesion between the molded body and the mold, and forming the molded body and the mold. And a mold with high precision.
As the conductive ceramics used in the present invention, commercially available conductive ceramics (ceramics generally called black ceramics) can be used. Preferable examples thereof include, for example, silicon carbide, titanium carbide, and tungsten carbide. As the conductive particles, for example, carbide, nitride, boride, and the like can be used, and metal particles and metal fibers can also be used. Examples of the material of the molded body used in the present invention include, for example, hardly sinterable materials such as metals and ceramics, and more specifically, titanium aluminide, titanium silicide, chromium silicide, and cermet alloy. Is done. However, the present invention is not limited to these, and the same can be used as long as it has the same effect.
[0009]
In the present invention, it is necessary to mix zirconium oxide with these conductive ceramics and to include zirconium oxide at least in a portion in contact with the compact. In this case, zirconium oxide is dispersed in the entire mold material, or zirconium oxide is dispersed in part or all of the portion in contact with the molded body. The dispersion method is not particularly limited, for example, a method of adding zirconium oxide powder when mixing the conductive ceramic powder, a method of joining a conductive ceramic containing zirconium oxide to the surface of the conductive ceramic mold, and the like. Is exemplified. If zirconium oxide is mixed in the portion in contact with the compact, a remarkable effect of remarkably improving the mold releasability can be obtained.
[0010]
DC or AC current can be used for the electric sintering. In the present invention, direct current is more effective because oxygen of zirconium oxide is moved by the flow of electricity. However, the oxygen contained in the zirconium oxide is released from the surface of the mold at any of the currents, so that a gap is formed between the molded body and the molded body, so that the molded body can be easily removed from the mold. Further, regarding the heating of the molded body, the molded body can be resistance-heated by the electric resistance of the mold itself.
[0011]
The temperature of the electrode is low because it is water-cooled.However, conductive ceramics are used for the part in contact with the molded body, and electrical resistance, thermal shock resistance, and heat conduction are applied between the conductive ceramic and the electrode. By inserting substances having different physical properties such as the rate, the crystal grain can be controlled by controlling the cooling rate of the sintered body. As these substances having different physical properties, for example, cermet alloy, cast iron, carbon particle-dispersed composite metal and the like are preferably used. Alloys and the like can also be used. Even if a substance having different physical properties is inserted between the mold and the electrode, the effect of the present invention does not change as long as electricity flows. Further, in the present invention, a conductive ceramic containing zirconium oxide can be used in a part in contact with the molded body, but this allows the molded body to be produced without breaking the current path even if a large temperature difference occurs. be able to.
[0012]
In electric sintering, molding is generally performed by heating while applying pressure while applying pressure.However, with conventional conductive ceramic molds, cracking or peeling occurs when the molded body is removed from the mold, and processing accuracy and dimensions are limited. there were. However, by utilizing the oxygen transfer due to energization of zirconium oxide, the separation between the mold and the molded body is improved, and the processing accuracy can be dramatically increased. Since conductive ceramics have excellent hardness even if they contain zirconium oxide, the surface shape of the mold can be transferred to the surface of the molded body with high accuracy, and therefore, it is possible to perform processing of fine shapes. .
[0013]
The atmosphere used for the electrical sintering is not particularly specified, but when the molded body is a metal material or a metal-based composite material, a vacuum atmosphere is used, and when the molded body is a ceramic, vacuum, oxygen, An atmosphere such as nitrogen can be used. There is no problem even if pressure is applied during electric sintering, and pressurization is an effective means for improving the surface accuracy of the compact.
[0014]
Conductive ceramics are widely used, and a method of adding zirconium oxide has been put to practical use in an attempt to improve the strength, but in the present invention, zirconium oxide is regarded as a transfer source of oxygen and oxidized. Zirconium does not contribute to mold strengthening. Therefore, zirconium oxide is originally white, but in the present invention, zirconium oxide changes to gray or black due to the movement of oxygen.
[0015]
Oxygen that has moved from the inside of the mold to the surface of the mold according to energization is released as a gas between the mold and the molded body. Therefore, a slight gap occurs between the mold and the molded body, and the molded body can be easily taken out of the mold. The gap between the compact and the mold depends on the amount of gas generated, but is considered to be several microns or less. Since the gas generated from the mold pushes the molded body, this mechanism can be used to join the molded body onto another substance. Examples of these include, but are not limited to, a method of bonding titanium to the surface of a stainless steel material, a method of bonding TiC-Ni (cermet alloy) to the surface of titanium, and the like. Also, at the time of joining, separation from the mold is easy, and these joined bodies can be easily removed from the mold.
[0016]
【Example】
Next, the present invention will be specifically described based on examples, but the present invention is not limited to the following examples.
Example 1
5 g of titanium powder (manufactured by Kojundo Chemical) is placed in a graphite die having an outer diameter of 30 mm, an inner diameter of 15 mm, and a height of 30 mm, and zirconium oxide of 20% by mass is added to a 15 mmφ × 5 mm TiC powder, a SiC powder, and a Ni powder. The added conductive ceramic sintered body was used as upper and lower punches in a portion that comes in contact with the molded body, and between the electrodes was electrically sintered using graphite of 15 mmφ × 20 mm. Sintering was performed by using a pulsed direct current for energization so that the temperature of the graphite die was 800 ° C. During sintering, a pressure of 30 MPa was applied, and the sintering atmosphere was set to a vacuum of about 20 Pa.
[0017]
By using the conductive ceramics for the punch, it was possible to heat to the target temperature with an output of 80% or less as compared with the molding of the graphite mold alone. Also, the time required to reach the target temperature was 70% or less at the same current value.
The surface of the conductive ceramic punch was mirror-polished, but the surface of the obtained molded product was slightly discolored due to oxidation. The molded body could be easily removed from the punch, and the surface had a surface roughness of the degree of mirror polishing. In addition, the conductive ceramic did not crack and could be used repeatedly. The molded article had a density of 98% or more of the theoretical density.
[0018]
Example 2
5 g of Ti-36% by mass Al powder (mechanical alloying synthetic powder) is placed in a graphite die having an outer diameter of 30 mm, an inner diameter of 10 mm, and a height of 30 mm, and the surface of a 10 mmφ × 15 mm graphite punch in contact with the molded body. Then, electric current sintering was performed using titanium carbide and zirconium oxide slurried with ethyl alcohol and applied. The coating film was about 1.5 mm. Sintering was performed by using a pulsed direct current for energization and controlling the temperature of the graphite die to 800 ° C. During sintering, a pressure of 40 MPa was applied. The sintering atmosphere was a vacuum of about 20 Pa.
[0019]
Discoloration was slightly observed on the surface of the molded body in contact with the surface coated with zirconium oxide and titanium carbide, but the punch was easily separated from the molded body. The coating film was initially gray, but turned black after sintering. The compact had a density of 95% or more of the theoretical density.
[0020]
Example 3
A 15 mm x 1 mm stainless steel plate is placed in a graphite die with an outer diameter of 30 mm, an inner diameter of 15 mm, and a height of 30 mm, and 5 g of titanium powder (manufactured by Kojundo Chemical) is placed. A zirconium sintered body was installed. 15 mmφ × 20 mm graphite was used between the electrodes, and this was used as a punch to perform electric sintering. Black zirconium oxide can be produced by commercially available zirconium oxide powder partially stabilized with yttrium oxide by current sintering using a graphite type punch in a vacuum of about 10 Pa. 2 shows the X-ray diffraction pattern of FIG. This black zirconium oxide is slightly conductive even at room temperature, and can be electrically sintered. Sintering was performed by using a direct current for energization so that the temperature of the graphite die was 800 ° C. During sintering, a pressure of 40 MPa was applied. The sintering atmosphere was a vacuum of about 20 Pa.
[0021]
The obtained molded body had titanium bonded to the stainless steel surface. Since stainless steel did not melt at the above molding temperature, it could be easily separated from the graphite punch on the negative electrode side. On the positive electrode side, since oxygen was released from zirconium oxide, no welding of titanium and graphite or zirconium oxide was observed. When the oxygen content in the inside of the zirconium oxide on the positive electrode side was measured, the distribution was as shown in FIG. 2, and the movement of oxygen along the flow of electricity was confirmed. Titanium was easily removed from the mold, and the density of the compact became 95% or more.
[0022]
【The invention's effect】
As described in detail above, the present invention relates to a mold material used for conducting electric sintering, a method for producing a molded member using the same, and a molded member. By using a conductive material containing zirconium oxide for the mold in the above, hardly sinterable materials such as metals and ceramics can be easily solidified and molded. 2) In particular, oxygen is released from zirconium oxide when electricity is supplied. By using the phenomenon of moving according to the flow of electricity, the molded body can be easily separated and collected from the mold without applying a mold release material to the mold. 3) The surface of the obtained molded body is Although it is slightly oxidized, as a result, the hardness of the surface can be improved. 4) Since a release material is not used, a high-precision molded body can be produced. 5) The acid used in the present invention. The conductive ceramics type containing zirconium has higher electric resistance than the graphite type generally used in current-phase sintering, and can carry out large heating in a short time with small energy. 6) When fabricating high-precision and fine members such as micromachines, the technology of the present invention is a method for facilitating separation from a mold. This is a special effect that is useful.
[Brief description of the drawings]
FIG. 1 shows an X-ray diffraction pattern of black zirconium oxide.
FIG. 2 shows the amount of oxygen in zirconium oxide.

Claims (8)

A mold material with excellent mold release properties used when producing a molded body by sintering the molding material while energizing, and using conductive ceramics containing zirconium oxide in the part in contact with the molded body A high mold release material characterized by the following. The mold material according to claim 1, which is a mold material used when performing sintering by direct current. A method for producing a molded member using the mold material according to claim 1 or 2, wherein the molded material is sintered while being energized to produce a molded body. A conductive ceramic containing zirconium oxide is used in the contacting part, and oxygen is transferred from the inside of the mold to the surface of the mold by applying a current between the electrodes to generate gas between the mold and the molded body, and the gas is generated from the mold. A method for producing a molded member, comprising releasing a molded body by utilizing the pressure of the generated gas. 4. The method according to claim 3, wherein a material having a different electric resistance from the ceramic is used between the conductive ceramic and the electrode. 4. The method according to claim 3, wherein the sintering is performed by a direct current. The method according to claim 3, wherein a conductive ceramic containing zirconium oxide is used in a part in contact with the molded body. The molding material and another substance are put into a mold, and the molding material is formed into a molded body, and the molded body is joined to another substance by using the pressure of gas generated from the mold to form a composite. Item 3. The method according to Item 3. A molded member produced by the method according to any one of claims 3 to 7, wherein a surface fine shape of a mold is transferred with high accuracy.

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