JPH10231174A - Composite ceramic including dispersed solid lubricant and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a composite ceramic excellent in mechanical strength and friction characteristic and having a dense structure, by dispersing a solid lubricant such as carbon in a nonoxide ceramic mother phase such as silicon nitride and further putting an iron compound in the interface part of the both phases. SOLUTION: This composite ceramic is formed by dispersing a solid lubricant phase 4 comprising at least one selected from between graphite and boron nitride in a mother phase 2 comprising nonoxide ceramics such as silicon nitride, silicon carbide and sialon, and further putting an iron compound phase 3 such as an oxide and silicide of iron having compatibility with the both phases in the interface part of the both phases. The composite ceramic 2 is produced by previously coating the surface of the solid lubricant with the iron compound, formulating the coated solid lubricant with the silicon nitride powder raw material, forming a compact of the formulated silicon nitride powder raw material and firing the compact. Moreover, the iron compound phase 3 comprises an iron compound phase 3a enclosing the solid lubricant phase 4 and having a large particle diameter, and a fine iron compound phase 3b comprising only the iron compound, and the iron compound phase 3b acts as an adsorbing phase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite ceramic having excellent mechanical strength and friction characteristics, and more particularly to a composite ceramic in which a solid lubricant is dispersed and a method for producing the same.

[0002]

2. Description of the Related Art Heretofore, there has been known one in which particles of a solid lubricant such as boron nitride (BN) and carbon (C) are dispersed in ceramics containing silicon nitride as a main component.

[0003] When boron nitride particles as a solid lubricant are dispersed in ceramics such as silicon nitride, the amount of boron nitride added is limited to a small amount, and hot press molding is required to densify the structure. It is not suitable for manufacturing large parts. In addition, when carbon powder is added to the silicon nitride powder raw material and fired, the silicon nitride reacts with carbon to fire silicon carbide, and a part of the reactant is released as gas to the outside. Therefore, the tissue becomes porous, and a high-strength material cannot be obtained.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a composite ceramic having a dense structure and a solid lubricant such as boron nitride dispersed in a non-oxide ceramic such as silicon nitride. It is to provide a manufacturing method thereof.

[0005]

In order to solve the above-mentioned problems, the present invention relates to a method in which a matrix composed of non-oxide ceramics such as silicon nitride, silicon carbide, and sialon includes at least one of carbon and boron nitride. One solid lubricating phase is dispersed, and iron compounds such as iron oxide and iron silicide are dispersed at a boundary between the mother phase and the solid lubricating phase. .

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, an excellent affinity between the matrix and the solid lubricating phase such as graphite and boron nitride is formed at the boundary between a matrix composed of non-oxide ceramics such as silicon nitride, silicon carbide and sialon. Intermediate iron compound. For this purpose, the surfaces of solid lubricant particles such as graphite and boron nitride are coated in advance with an iron compound and then mixed with the silicon nitride powder raw material, or the iron compound particles in which the solid lubricating phase is dispersed are coated with silicon nitride powder. It is blended with a raw material, a molded body is produced from this blended raw material, and fired at a low temperature. Iron changes to iron silicide by firing, but iron silicide has a good affinity for both the solid lubricating phase and silicon nitride, and a dense structure without defects can be obtained. In other words, the solid lubricating phase is dispersed in the matrix composed of non-oxide ceramics,
A dense composite ceramics of the tissue can be obtained.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The composite ceramics according to the present invention comprises a solid phase composed of at least one of carbon and boron nitride dispersed in a non-oxide ceramic such as silicon nitride, silicon carbide or sialon as a matrix. Iron compounds such as iron oxide and iron silicide are dispersed at the boundary between the phase and the solid lubricating phase.

In the embodiment shown in FIG. 1, an iron compound phase 3 is dispersed in a mother phase 2 made of silicon nitride as a ceramic, and the iron compound phase 3 is a solid lubricant made of carbon which is a solid lubricant. Iron compound phase 3a having a large particle diameter enclosing phase 4 and fine iron compound phase 3b containing only iron compound
And the iron compound phase 3b acts as an adsorption phase.

The composite ceramics in which the solid lubricant is dispersed according to the present invention and a method for producing the same will be described based on specific examples.

[Example 1] As a solid lubricant, 4.8%
The spheroidal graphite cast iron containing carbon was atomized to obtain a powder having a particle diameter of 10 μm. The particle size of the spheroidal graphite cast iron powder was reduced to 5 μm while dissolving the iron content of the spheroidal graphite cast iron powder by chemical treatment. Sulfur nitride (SN) is used as the main raw material. Sulfur nitride (SN), an oxide auxiliary such as alumina (sintering auxiliary), and iron oxide are mixed and granulated. A required molded body is produced from the product by CIP molding (hydrostatic molding), and the molded body is heated to a temperature of 1
The mixture was fired in a nitrogen atmosphere at 700 ° C. to obtain a composite ceramic. As shown in FIG. 1, it is confirmed by SEM (scanning electron microscope) that the structure of the obtained composite ceramics has no pores and a graphite phase exists inside the iron oxide phase 3a.

As shown in Table 1, the amount of the atomized spheroidal graphite cast iron powder added to the total amount of the raw material was 4%.
If it exceeds 0 wt%, traces of iron melting and blowing out after sintering are observed.

[0012]

[Table 1] Example 2 As a solid lubricant, the surface of graphite particles was coated with iron using an iron alkoxide solution. In the same process as in Example 1, silicon nitride as a main raw material was mixed with graphite particles obtained by coating with iron, an oxide auxiliary such as alumina, and iron oxide, and then granulated. A molded body produced from the particles of the mixture by CIP molding was fired in a nitrogen atmosphere at a temperature of 1700 ° C. to obtain a composite ceramic. The obtained composite ceramics was a dense sintered body, and it was confirmed that the graphite phase was dispersed in the mother phase of the sintered body. The resulting composite ceramics had an average four-point bending strength of 850 MPa.

Example 3 A composite ceramic in which boron nitride was dispersed in silicon nitride was obtained by the same process as in Example 2 using boron nitride powder as a solid lubricant. The average 4-point bending strength of the obtained composite ceramics is 812MP.
a.

The friction characteristics of the composite ceramics obtained in Examples 1 to 3 are as shown in FIG. 2, from which the composite ceramics in which the solid lubricating phase according to the present invention is dispersed has a friction coefficient in the boundary lubrication region. It turns out to be very small.

[Comparative Example 1] Graphite particles and boron nitride particles were separately used as solid lubricants, and each was added to a silicon nitride powder by the same process as in Example 2, and was prepared from each mixed powder by CIP molding. The formed body was fired in a nitrogen atmosphere at a temperature of 1700 ° C. to obtain a composite ceramic in which graphite was dispersed in silicon nitride and a composite ceramic in which boron nitride was dispersed in silicon nitride. Each of the obtained composite ceramics had pores of 15% or more, and the average four-point bending strength of each composite ceramic was 366 MPa and 380 MPa.

Example 4 As a solid lubricant, phenol, formaldehyde and ammonia were mixed with triiron tetroxide (Fe
304) The powder was added and mixed, and the mixed powder was heat-treated and then crushed to obtain iron-graphite composite particles. By the same process as in Example 1, sulfur nitride (S
N), the above-mentioned composite particles of iron-graphite, an oxide auxiliary such as alumina, and an oxide of iron are mixed and granulated, and then a molded product produced by CIP molding from the particles of the mixture. Was fired in a nitrogen atmosphere at a temperature of 1700 ° C. to obtain a composite ceramics in which iron-graphite composite particles were dispersed in a matrix composed of silicon nitride. The obtained composite ceramics had an average four-point bending strength of 790 MPa and a friction coefficient in the boundary lubrication region of 0.06, indicating a good result.

[Example 5] Using silicon carbide and sialon as main raw materials separately, by the same process as in Example 2,
Composite ceramics in which solid lubricant particles were dispersed in a matrix made of silicon carbide and composite ceramics in which solid lubricant particles were dispersed in a matrix made of Sialon were fired. The average four-point bending strength of each of the obtained composite ceramics was 652 MPa and 769 MPa, the friction coefficient was 0.07,
A good result of 0.06 was obtained.

Comparative Example 2 A graphite powder and a boron nitride powder were separately used as solid lubricants, and compounded with silicon nitride powder without interposing an iron compound on or near the surface of these powders. By the same process as above, composite ceramics in which graphite is dispersed in silicon nitride,
The composite ceramics in which boron nitride was dispersed in silicon nitride was fired. Each of the obtained composite ceramics became porous even when the amount of graphite or boron nitride was changed, and the average four-point bending strength was 332 MPa and 411, respectively.
It was as low as MPa, and the friction coefficient was 0.11.

[0019]

As described above, according to the present invention, a solid lubricating phase composed of at least one of carbon and boron nitride is dispersed in a matrix composed of non-oxide ceramics such as silicon nitride, silicon carbide and sialon. An iron compound such as an oxide of iron or a silicide of iron is dispersed at a boundary portion between the mother phase and the solid lubricating phase. Since an iron compound having an excellent affinity for both is present at the boundary between the two, a dense structure without defects can be obtained, and a composite ceramic having excellent mechanical strength and friction characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view showing the structure of a composite ceramic in which a solid lubricant according to the present invention is dispersed.

FIG. 2 is a diagram showing friction characteristics of a composite ceramics according to the present invention and a conventional example.

[Explanation of symbols]

 2: Mother phase 3: Solid lubricating phase

Claims (7)

[Claims] A solid lubricating phase composed of at least one of carbon and boron nitride is dispersed in a matrix composed of non-oxide ceramics such as silicon nitride, silicon carbide and sialon. A composite ceramic in which a solid lubricant is dispersed, wherein an iron compound such as an oxide of iron and a silicide of iron is dispersed in a boundary portion of the solid lubricating phase. 2. An iron compound having a large particle diameter which contains a solid lubricating phase composed of at least one of carbon and boron nitride in a matrix composed of non-oxide ceramics such as silicon nitride, silicon carbide and sialon. A composite ceramic in which a solid lubricant is dispersed, characterized in that a phase and a fine iron compound phase containing only an iron compound are dispersed. 3. The composite ceramic in which the solid lubricant is dispersed according to claim 1, wherein the amount of the iron compound added is 35 wt% or less. 4. A process for preparing particles in which a phase containing an iron compound is formed on the outer peripheral surface of graphite particles or boron nitride particles, and after mixing the non-oxide ceramics, the particles and a sintering aid. A method for producing a composite ceramic in which a solid lubricant is dispersed, comprising a step of molding and firing. 5. The method according to claim 4, wherein the step of producing the particles having a phase containing a compound of iron is produced by atomization using a cast iron block as a raw material. . 6. The step of producing particles in which a phase containing an iron compound has been formed comprises immersing graphite particles or boron nitride particles in an iron-containing alkoxide solution or iron nitrate solution, followed by heat treatment to form a film. A method for producing a composite ceramic in which the solid lubricant according to claim 4 is dispersed. 7. The composite ceramic in which the solid lubricant is dispersed according to claim 4, wherein the step of producing particles in which a phase containing a compound of iron has been formed is heat-treated after dispersing the iron compound particles in formaldehyde and phenol. Manufacturing method.