JP2011068538A - Method for producing titanium silicon carbide ceramic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive mass production technique in the synthesis of a titanium silicon carbide ceramic member by normal pressure sintering of a mixed powder of titanium, silicon carbide, and carbon by solving a problem of the occurrence of component segregation in the height direction (vertical direction) of the member. <P>SOLUTION: To a mixed powder of titanium, silicon carbide, and carbon corresponding to the stoichiometry of titanium silicon carbide (Ti<SB>3</SB>SiC<SB>2</SB>), an element undergoing eutectic reaction with titanium such as silicon, as a liquid phase-forming component, and an element which has a low melting point and can replace the site of silicon of titanium silicon carbide such as aluminum are added. The resulting mixture is formed into a compression molded product, which is then subjected to normal pressure sintering to synthesize the titanium silicon carbide ceramic member. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing titanium silicon carbide ceramics, and more particularly, to provide a production method suitable for mass production of titanium silicon carbide ceramic members which are dense and have little component segregation.

Titanium silicon carbide ceramics is mainly composed of titanium silicon carbide (Ti ₃ SiC ₂ ), and titanium carbide (TiC), pentatitanium trisilicate (Ti ₅ Si ₃ ), titanium disilicide (TiSi ₂ ) as impurities. Ceramics containing a small amount of silicon carbide (SiC) and the like. It is a conductive machinable ceramic that exhibits metal conductivity (conductivity by free electrons) and can be cut like graphite, and is expected as a functional material and a structural material. Titanium silicon carbide ceramics are titanium, silicon, carbon, or titanium, silicon, titanium carbide, or titanium, silicon carbide, carbon, or mixed powder of titanium, silicon carbide, titanium carbide at atmospheric pressure or pressure sintering (For example, Documents 1, 2, and 3).

  In the synthesis by pressure sintering, the raw material mixed powder is put into a heat-resistant mold such as a graphite mold and heated while being pressurized, and simultaneously sintered and densified. Alternatively, the raw material mixed powder is compression-molded by a mold press, or put in a rubber mold and compression-molded by a hydrostatic pressure press (Cold Isostatic Press, abbreviated as CIP), which is vacuum-sealed in a glass capsule or a metal capsule, It is heated while being pressed by a hot isostatic press (HIP), and simultaneously sintered and densified. Therefore, it is possible to synthesize dense titanium silicon carbide ceramics having a relative density (the ratio of the actual density to the theoretical density in percentage) of 99% or more. However, the pressure sintering method has low productivity and high cost, and cannot be said to be a method suitable for mass production.

  On the other hand, in the synthesis by atmospheric pressure sintering, the raw material mixed powder is compression-molded by a mold press, or put in a rubber mold and compressed by an isostatic press (CIP), and this is vacuum or atmospheric pressure in a heating furnace. Heat in inert gas and sinter and densify simultaneously with synthesis. Although the relative density of titanium silicon carbide ceramics synthesized because it is not pressurized is low, the atmospheric pressure sintering method is high in productivity, low in cost, and suitable for mass production.

However, the normal pressure of the mixed powder corresponding to the stoichiometric composition of titanium silicon carbide (Ti ₃ SiC ₂ ), the weight ratio of titanium: silicon carbide: carbon = 73.4: 20.5: 6.1 (molar ratio 3: 1: 1) In the synthesis by sintering (Reference 3), it is possible to synthesize titanium silicon carbide ceramics having a relative density of 97% or more, but in a laboratory, a small disk-shaped member having a weight of about 2 g, a diameter of 14 mm, and a thickness of about 4 mm This result was obtained based on synthesis, and it was found that segregation of components occurred in the height direction (vertical direction) of the composite member as the height of the molded body increased. For example, as shown in FIG. 1, a mixed powder of titanium, silicon carbide, and carbon corresponding to the stoichiometric composition of titanium silicon carbide (Ti ₃ SiC ₂ ) is mixed with a mold at a pressure of 400 MPa or 500 MPa and a weight of about 7. When compression molding is performed on a cylindrical member having a diameter of 4 g, a diameter of about 14 mm, and a length of about 15 mm, and the axial direction of the cylinder is vertical, and sintered at normal pressure in 0.1 MPa argon gas, X on the upper surface of the cylinder In the line diffraction pattern, in addition to the diffraction peak of titanium silicon carbide, a diffraction peak of strong titanium carbide (TiC) is seen, and its content is 15.5% by volume, whereas X-rays on the bottom of the cylinder It can be seen that the peak of titanium carbide in the diffraction pattern is slight, the content is only 1.0% by volume, and segregation of components occurs in the vertical direction. Thus, in the conventional method for producing titanium silicon carbide by atmospheric pressure sintering, for example, as the height of the molded body increases, segregation of components occurs in the height direction of the synthetic member, and the structural material, functional material, etc. It was difficult to obtain compatible titanium silicon carbide.

JP 2003-2745 A Japanese Patent No. 3995143 JP 2005-89252 A

  It is an object of the present invention to overcome the above-mentioned problems of the prior art and to provide a method capable of producing large quantities of titanium silicon carbide members with high industrial utility value, dense, and less segregation by atmospheric pressure sintering. It is said.

The present invention for solving the above problems is characterized by comprising the following technical means.
(1) A mixed powder of titanium, silicon carbide, and carbon, (a) an element that forms a liquid phase by eutectic reaction with titanium, and / or (b) a silicon site of titanium silicon carbide with a low melting point. A method for producing a titanium silicon carbide ceramic member, comprising compression-molding a mixture containing an element that can be formed and then sintering at normal pressure.
(2) (a) Elements that form a liquid phase by eutectic reaction with titanium are silicon, iron, and cobalt, and (b) an element that has a low melting point and can replace silicon sites in titanium silicon carbide is aluminum. The manufacturing method of the titanium silicon carbide ceramic member as described in said (1).
(3) The method for producing a titanium silicon carbide ceramic member according to (1), wherein the composition of the mixed powder of titanium, silicon carbide, and carbon corresponds to the stoichiometric composition of titanium silicon carbide (Ti ₃ SiC ₂ ).
(4) The titanium silicon carbide ceramic member according to any one of (1) to (3), wherein the atmospheric pressure sintering temperature is in the range of 1200 to 1500 ° C. and the sintering temperature holding time is in the range of 30 minutes to 6 hours. Manufacturing method.

  The method of the present invention having the features as described above is based on the new knowledge obtained from the experimental investigation by the inventors with the following details.

That is, the inventor first examines a synthesis process of titanium silicon carbide ceramics by heating a compression molded body of a mixed powder of titanium, silicon carbide, and carbon corresponding to the stoichiometric composition of titanium silicon carbide (Ti ₃ SiC ₂ ). Therefore, a small cylindrical compression molded body having a weight of about 5 g, a diameter of 14 mm, and a length of about 11.5 mm is heated to a predetermined temperature in the range of 750 ° C. to 1550 ° C. at a temperature rising rate of 20 ° C. in a vacuum, Quenched quickly. The X-ray diffraction pattern of this sample was measured to identify the formation phase at each temperature. As shown in FIG. 2, titanium silicide (mainly trititanium pentasilicate Ti ₅ Si ₃ ) and carbonized from around 850 ° C. It was found that after titanium TiC was formed, titanium silicide and titanium carbide reacted at about 1350 ° C. to synthesize titanium silicon carbide. Formation of titanium silicide and titanium carbide from around 850 ° C. is a result of observation by a scanning electron microscope (SEM) and analysis by an energy dispersive X-ray analyzer (EDX) of a sample in which the sample is embedded in a resin and the cross section is polished. It is considered that silicon and carbon are diffused into the inside of the titanium particles from the silicon carbide particles and the carbon particles in contact with the titanium particles (references: Hitachi Hashimoto, Zheng Ming Sun, Shuji Tada, “Morphological Evolution Singing Reaction Reaction Sintering and C Powder Blend ", Journal of Alloys and Compounds, Vol. 441, pp. 174-180, (2007)). However, since titanium and carbon are a combination that causes a solid-phase reaction to produce titanium carbide, it is considered that this solid-phase reaction also occurs along with diffusion.

  As already shown in FIG. 1, the cause of the segregation of components in the height direction (vertical direction) of the composite member as the member height increases is considered as follows. In the synthesis process, it is considered that the titanium-silicon alloy and titanium silicide produced by the diffusion of silicon into the titanium particles are dissolved at a eutectic temperature of about 1330 ° C., and a liquid phase is generated. The resulting liquid phase promotes densification of the member by surface tension, but moves to the lower part of the member due to the influence of gravity. Therefore, it is considered that titanium silicide is insufficient and titanium carbide remains at the upper part of the member.

That is, the shortage of the liquid phase is considered to cause vertical component segregation. Therefore, in order to increase the liquid phase, silicon which is an element causing a eutectic reaction with titanium and aluminum which is an element capable of substituting the silicon atom site of titanium silicon carbide crystal with a low melting point metal are selected, either alone or together, A small amount was added to a mixed powder of titanium, silicon carbide, and carbon corresponding to the stoichiometric composition of titanium silicon carbide (Ti ₃ SiC ₂ ). As a result, it was found that the segregation of the component in the height direction was improved by the addition.

  The effectiveness of such elements other than silicon and aluminum was also evaluated.

  Industrial Applicability According to the present invention, a titanium silicon carbide ceramic member having high industrial utility value, dense and less segregation of components can be produced at low cost and in large quantities.

A cylindrical molded body obtained by compression molding a mixed powder of titanium, silicon carbide, and carbon corresponding to the stoichiometric composition of titanium silicon carbide (Ti ₃ SiC ₂ ) with a mold is usually used in a state where the axial direction of the cylinder is vertical. X-ray diffraction pattern of the bottom and top surfaces of the sintered and synthesized sample Sintering obtained from an X-ray diffraction pattern of a sample synthesized by compression-sintering a compact of titanium, silicon carbide and carbon mixed powder corresponding to the stoichiometric composition of titanium silicon carbide (Ti ₃ SiC ₂ ) Phase change diagram with temperature and reaction path estimated from the figure A compression molded body obtained by compression molding a mixed powder obtained by adding 1 mass% or 2 mass% of silicon powder to a mixed powder of titanium, silicon carbide, and carbon corresponding to the stoichiometric composition of titanium silicon carbide (Ti ₃ SiC ₂ ). , X-ray diffraction pattern of the top and bottom surfaces of the sample synthesized by placing the cylinder in the vertical direction and sintering at normal pressure A compression molded body obtained by compression molding a mixed powder obtained by adding 1% by mass or 2% by mass of aluminum powder to a mixed powder of titanium, silicon carbide, and carbon corresponding to the stoichiometric composition of titanium silicon carbide (Ti ₃ SiC ₂ ). , X-ray diffraction pattern of the top and bottom surfaces of the sample synthesized by placing the cylinder in the vertical direction and sintering at normal pressure Mixed powder obtained by adding 2% by mass of silicon powder and 1% by mass of aluminum powder (total 3% by mass) to a mixed powder of titanium, silicon carbide and carbon corresponding to the stoichiometric composition of titanium silicon carbide (Ti ₃ SiC ₂ ) An X-ray diffraction pattern of the top and bottom surfaces of a sample synthesized by placing the compression molded body of Mixed powder obtained by adding 4% by mass of silicon powder and 1% by mass of aluminum powder (total 5% by mass) to a mixed powder of titanium, silicon carbide, and carbon corresponding to the stoichiometric composition of titanium silicon carbide (Ti ₃ SiC ₂ ) An X-ray diffraction pattern of the top and bottom surfaces of a sample synthesized by placing the compression molded body of

  Next, the present invention will be described in more detail.

  The present invention provides a manufacturing method suitable for mass production of a titanium silicon carbide ceramic member having a high industrial utility value, being dense and having little segregation of components.

  The production method of the present invention eliminates the liquid phase shortage that is considered to be the cause of component segregation, and an element that causes a eutectic reaction with titanium and an element that can replace the silicon atom site of titanium silicon carbide crystal with a low melting point metal Add a small amount to a mixed powder of titanium, silicon carbide, and carbon, either alone or together, and mix them well to produce a compression molded body, which is then fired at normal pressure in an inert atmosphere such as vacuum or argon gas. It is a way to tie.

  Here, silicon (Si) can be cited as a typical example of an element that causes a eutectic reaction with titanium (Ti). Examples of other elements include iron (Fe) and cobalt (Co). Although the range of the optimum addition amount of these elements varies depending on the element, in the case of single addition, it is usually added in a range of 0.9 mass% or more and less than 3 mass% with respect to the raw material mixed powder. If it is less than 0.9%, the effect of preventing component segregation tends to be insufficient, and if it is 3% or more, substances other than titanium carbide are synthesized and the purity of titanium silicon carbide is reduced, or a rapid exothermic reaction occurs and does not become dense. Such harmful effects are likely to occur.

  On the other hand, aluminum (Al) can be cited as an element capable of substituting the silicon atom site of the titanium silicon carbide crystal.

  In the case of single addition, aluminum is usually added in a range of 1% by mass or more and less than 2% by mass with respect to the raw material mixed powder. If it is less than 1%, the effect of preventing component segregation is insufficient, and if it is 2% or more, there is a problem that densification becomes uneven.

  On the other hand, when both Si, which is an element that causes a eutectic reaction with Ti, and Al, which is an element that can replace the site of the silicon atom of the titanium silicon carbide crystal, are added in a total amount of 2 mass% or more and 6 mass in total. %, More preferably in the range of 3 to 5% by mass. If it is less than 1%, the effect of preventing component segregation is insufficient, and if it is 6% or more, substances other than titanium carbide are also synthesized, and adverse effects such as a decrease in the purity of titanium silicon carbide tend to occur.

  The mixed powder as a raw material to which the above elements are added has a composition of titanium, silicon carbide, and carbon, and their blending preferably has a stoichiometric composition (molar ratio) of titanium silicon carbide.

  Regarding the constituents of these mixed powders and the above-mentioned elements, the particle size at the time of mixing may generally be in the range of 100 μm or less, and the mixing method may be appropriately selected from various known methods.

  The mixing time varies depending on the amount of powder, but is about 1 to 50 hours. This mixed powder is compression molded with a mold and a press. The molding pressure varies depending on the shape and dimensions of the mold, but is in the range of 200 to 500 MPa. The molded body is placed in a stable posture and sintered at normal pressure in an inert atmosphere such as vacuum or argon gas. The sintering temperature is desirably in the range of 1200 ° C to 1500 ° C. When the sintering temperature is less than 1200 ° C., the synthesis reaction and sintering are not sufficient, and there are a large amount of intermediate products of titanium silicide and titanium carbide. On the other hand, if the sintering temperature exceeds 1500 ° C., crystal grains become coarse and energy consumption increases, which is useless. A more preferable sintering temperature is a sintering temperature of 1400 to 1500 ° C.

  The holding time at the sintering temperature is 0.5 hours to 6 hours. The sintering holding time is determined in relation to the sintering temperature, but if it is less than 0.5 hours, the synthesis reaction is not sufficient, and if it exceeds 6 hours, the crystal grains become coarse, which is not preferable. A more preferable sintering time is in the range of 2 hours to 3 hours.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples. That is, the present invention includes all aspects or modifications other than the following examples as long as the technical idea is within the scope of the invention.

A pressure of 400 MPa is applied to each mixed powder obtained by adding 1% by mass or 2% by mass of silicon powder to a mixed powder of titanium, silicon carbide, and carbon corresponding to the stoichiometric composition of titanium silicon carbide (Ti ₃ SiC ₂ ). And a cylindrical sample having a weight of about 7 g, a diameter of about 14 mm, and a length of about 15 mm was obtained. This was placed in an alumina container so that the axial direction of the cylinder was vertical, and heated in a high-purity argon gas of 0.1 MPa using a heat treatment furnace at 1500 ° C. for 2 hours. The top and bottom surfaces of the cylindrical sample after the heat treatment were polished and made flat, and then the X-ray diffraction patterns on the top and bottom surfaces were measured with an X-ray diffractometer. As a result, as shown in FIG. 3, almost only the X-ray diffraction peak of titanium silicon carbide (Ti ₃ SiC ₂ ) is recognized on the bottom surface of the upper surface, and there is no segregation of components in the axial direction (height direction) of the cylindrical sample. I understood it.

A mixed powder obtained by adding 1% by mass or 2% by mass of aluminum powder to a mixed powder of titanium, silicon carbide, and carbon corresponding to the stoichiometric composition of titanium silicon carbide is compression-molded with a mold at a pressure of 400 MPa, and has a weight of about 7 g. A cylindrical sample having a diameter of about 14 mm and a length of about 15 mm was obtained. This was placed in an alumina container so that the axial direction of the cylinder was vertical, and heated in a high-purity argon gas of 0.1 MPa using a heat treatment furnace at 1500 ° C. for 2 hours. The top and bottom surfaces of the cylindrical sample after the heat treatment were polished and made flat, and then the X-ray diffraction patterns on the top and bottom surfaces were measured with an X-ray diffractometer. As a result, as shown in FIG. 4, almost only the X-ray diffraction peak of titanium silicon carbide was recognized on the bottom surface of the top surface, and it was found that there was no segregation of components in the axial direction (height direction) of the cylindrical sample.

  A mixed powder obtained by adding 1% by mass of aluminum powder in addition to 2% by mass of silicon powder to a mixed powder of titanium, silicon carbide and carbon corresponding to the stoichiometric composition of titanium silicon carbide is compression-molded by a mold at a pressure of 200 MPa. A cylindrical sample having a weight of about 7 g, a diameter of about 14 mm, and a length of about 16 mm was obtained. This was placed in an alumina container so that the axial direction of the cylinder was vertical, and heated in a high-purity argon gas of 0.1 MPa using a heat treatment furnace at 1450 ° C. for 2 hours. The top and bottom surfaces of the cylindrical sample after the heat treatment were polished and made flat, and then the X-ray diffraction patterns on the top and bottom surfaces were measured with an X-ray diffractometer. As a result, as shown in FIG. 5, almost only the X-ray diffraction peak of titanium silicon carbide was observed on the bottom surface of the top surface, and it was found that there was no segregation of components in the axial direction (height direction) of the cylindrical sample.

  In Example 3, the composite was also produced when the addition amount was changed to Si (4%) and Al (1%). The X-ray diffraction pattern is shown in FIG.

  Almost the same result as in Example 3 was obtained.

  In Example 3, 0.9% by mass of iron powder or 1.1% by mass of cobalt powder was added instead of silicon powder and aluminum powder.

  Almost the same result as in Example 3 was obtained.

Comparative example

  A mixed powder of titanium, silicon carbide, and carbon corresponding to the stoichiometric composition of titanium silicon carbide is compression-molded with a mold at a pressure of 400 MPa and 500 MPa, and has a weight of about 7.4 g, a diameter of about 14 mm, and a length of about 15.3. A cylindrical sample of ˜15.8 mm was obtained. This was placed in an alumina container so that the axial direction of the cylinder was vertical, and heated in a high-purity argon gas of 0.1 MPa using a heat treatment furnace at 1500 ° C. for 2 hours. The top and bottom surfaces of the cylindrical sample after the heat treatment were polished and made flat, and then the X-ray diffraction patterns on the top and bottom surfaces were measured with an X-ray diffractometer. As a result, as already shown in FIG. 1, the bottom surface was almost only the X-ray diffraction peak of titanium silicon carbide, but the titanium carbide peak was also observed on the upper surface, and the axial direction (height direction of the cylindrical sample) ) Was found to be segregated.

  According to the present invention, it is possible to produce a titanium silicon carbide ceramic member having high industrial utility value, dense and less segregation of components at low cost and in large quantities. This makes it possible to develop structural materials and functional materials that take advantage of the unique properties of titanium silicon carbide ceramics. For example, heat treatment jigs that can be used in semiconductor manufacturing processes that take advantage of good thermal conductivity, high-temperature oxidation resistance as ceramics, chemical resistance and high-temperature stability, and easy cutting processability comparable to graphite, comparable to alumina ceramics High rigidity and vibration damping ability comparable to nylon, heavy duty vibration damping mounting material utilizing high temperature compressive strength comparable to titanium carbide, heater with complex shape utilizing electrical conductivity, high temperature oxidation resistance, easy cutting workability Application development that is impossible with conventional materials such as elements can be expected.

Claims (4)

  A mixed powder of titanium, silicon carbide, and carbon, (a) an element that forms a liquid phase by eutectic reaction with titanium, and / or (b) an element that has a low melting point and can replace silicon sites of titanium silicon carbide A method for producing a titanium silicon carbide ceramic member, comprising compression-molding a mixture containing sinter and sintering at normal pressure.   (A) The element that forms a liquid phase by eutectic reaction with titanium is silicon, iron, or cobalt, and (b) the element that has a low melting point and can replace the silicon site of titanium silicon carbide is aluminum. A method for producing a titanium silicon carbide ceramic member according to claim 1. _{2. The} method for producing a titanium silicon carbide ceramic member according to claim 1, wherein the composition of the mixed powder of titanium, silicon carbide, and carbon corresponds to a stoichiometric composition of titanium silicon carbide (Ti ₃ SiC ₂ ).   4. The titanium silicon carbide ceramic member according to claim 1, wherein the atmospheric pressure sintering temperature is in the range of 1200 to 1500 ° C. and the sintering temperature holding time is in the range of 30 minutes to 6 hours. 5. Production method.

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