JPH11310476A - Laminated type silicon nitride ceramic composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a laminated type silicon nitride ceramic composite material having enhanced strength of a material by reinforcing the structure of a surface layer and capable of being readily produced. SOLUTION: This silicon nitride ceramic composite material is obtained by laminating plural layers of silicon nitride ceramic comprising silicon nitride particles 2, 12 and oxynitride grain boundary phases 4, 14 containing silicon. The oxynitride grain phases 4, 14 are regulated so as to have different compositions, and the average particle size of the silicon nitride particles 2 at the surface layer 1 is regulated so as to be smaller than the average particle size of the silicon nitride particles 12 in the inner layer 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated silicon nitride ceramic composite material in which the strength and toughness of silicon nitride ceramics are systematically increased.

[0002]

2. Description of the Related Art In order to enhance the strength and toughness of silicon nitride ceramics, fiber-reinforced silicon nitride ceramics composite materials using silicon carbide fibers or carbon fibers as reinforcing fibers deteriorate reinforcing fibers at the time of sintering. It is difficult to control the interface between the fibers and the reinforcing fibers, and it is difficult to make them dense.

[0003] A laminated silicon nitride ceramic composite material in which a plurality of sheets in which silicon nitride particles are oriented is stacked, a seed crystal for orienting the silicon nitride particles is dispersed, and a hot press is used to sinter the laminate. The production method is complicated, for example, it is necessary to apply pressure.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a laminated silicon nitride ceramic composite material which is easy to manufacture and which has an enhanced structure by strengthening the surface layer structure. It is in.

[0005]

In order to solve the above-mentioned problems, the present invention has a structure in which a silicon nitride ceramic composed of silicon nitride particles and a silicon-containing oxynitride grain boundary phase is laminated in a plurality of layers. A composite material, wherein layers having different average particle sizes of the silicon nitride particles and different compositions of the oxynitride grain boundary phase are formed adjacent to each other, and the average particle size of the silicon nitride particles in the surface layer is It is characterized in that it is smaller than the average particle size of the silicon nitride particles in the inner layer.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The laminated silicon nitride ceramic composite material of the present invention is obtained by laminating and sintering a large number of silicon nitride sheet-like compacts having different components of sintering aids. In the silicon ceramic composite material, the particle size of the silicon nitride particles, the component of the grain boundary phase, and the melting point of the grain boundary phase are different for each layer. In particular, by reducing the average particle size of the silicon nitride particles in the surface layer, the structure is made dense and the strength is increased. Further, the toughness of the material is increased by increasing the average particle size of the silicon nitride particles in the inner layer.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a laminated silicon nitride ceramic composite material according to the present invention comprises silicon nitride particles 2,1.
And silicon oxynitride grain boundary phases 4 and 14, wherein layers having different average particle sizes of silicon nitride particles 2 and 12 and compositions of oxynitride grain boundary phases 4 and 14 are laminated. In particular, the average particle size of the silicon nitride particles 2 of the surface layer 1 is smaller than the average particle size of the silicon nitride particles 12 of the inner layer 11.

In order to obtain a laminated silicon nitride ceramics composite material according to the present invention, sheet-like molded articles A and B having different average particle sizes of silicon nitride particles and compositions of oxynitride grain boundary phases are prepared in advance. A large number of sheet-like molded articles A and B
Are superimposed as shown in FIG. 2 and pressed by an axial press to form a block-shaped molded product. After the obtained block-shaped molded body is degreased, it is fired in a nitrogen atmosphere at a temperature of 1700 ° C.

As shown in FIG. 3, a surface layer 1 comprises silicon nitride particles (crystal phase) 2 and aluminum, yttrium,
Iron, at least one of group 5 elements of the periodic table (long period type)
In particular, an oxynitride grain boundary phase 4 composed of tantalum and silicon,
Compound 5a containing Group 5 element dispersed in part or all of silicon nitride particles 2, Compound 6 containing iron and silicon dispersed in oxynitride grain boundary phase 4, and dispersed in oxynitride grain boundary phase 4 It is composed of a Group 5 element and a compound 5 containing silicon.

As shown in FIG. 4, the inner layer 11 includes silicon nitride particles 12, an oxynitride grain boundary phase 14 comprising at least one of aluminum, yttrium, iron and magnesium, silicon and manganese oxide, and an acid layer. It is composed of a compound 16 containing iron and silicon dispersed in the nitride grain boundary phase 14.

[Specific Example] A method for producing a laminated silicon nitride ceramic composite material according to the present invention will be described. A slurry is prepared by dispersing a raw material obtained by mixing a silicon nitride powder having a different particle size and a component of a grain boundary phase with a sintering aid powder in a solvent obtained by mixing toluene, ethanol, PVB and n-butyl phthalate. A plurality of types of sheet-like molded articles having a thickness of 200 μm were prepared from the slurry by a doctor blade device.

More specifically, a sheet-shaped compact A is prepared from a raw material obtained by mixing silicon nitride powder and powders of aluminum oxide, yttrium oxide, and tantalum oxide as sintering aids. A sheet-like molded body B is prepared from a raw material obtained by mixing powders of aluminum oxide, yttrium oxide and manganese oxide as sintering aids, and silicon nitride powder, aluminum oxide and manganese oxide as sintering aids are prepared. A sheet-shaped molded body C was prepared from a raw material obtained by mixing each of the powders of silicon and silicon oxide. A large number of these sheet-shaped compacts A and sheet-shaped compacts B or C were laminated and formed into a thickness of 4 mm by an axial press. After the obtained molded body was degreased, it was fired in a nitrogen atmosphere at a temperature of 1700 ° C. to obtain a silicon nitride ceramic composite material.

As shown in FIG. 1, the obtained silicon nitride ceramics composite material (product of the present invention) is a sheet-like molded product A
Are sintered to form the surface layer 1, and the sheet-like molded body B or C is sintered to form the inner layer 11. The particle size of the silicon nitride particles increased in order from the surface layer 1 to the inner layer 11. The formation temperature of the grain boundary phase 4 of the surface layer 1 is higher than the formation temperature of the grain boundary phase 14 of the inner layer 11. This is because, for the surface layer 1 and the inner layer 11, the softening point and viscosity of the grain boundary phases 4 and 14 are adjusted by changing the composition of the sintering aid, and the penetration of silicon nitride, phase transformation, reprecipitation, and grain growth are performed. This is the result of controlling the temperature and the speed of grain growth.

From the silicon nitride ceramics composite material according to the present invention (product of the present invention) and the conventional silicon nitride ceramics composite material (conventional product), test pieces of 3 × 4 × 40 mm were prepared, and the four-point bending strength of the test pieces was obtained. Test (JIS R1
601) and a toughness fracture test (ASTME399), as shown in FIGS. 5 and 6, the silicon nitride ceramic composite according to the present invention is superior in strength and toughness to the conventional silicon nitride ceramic composite. I found out.

Further, as a result of performing a four-point bending strength test using each of the above-mentioned test pieces having scratches (failure sources) of various sizes beforehand, as shown in FIG. The silicon ceramics composite material was found to be superior in breaking strength to the conventional silicon nitride ceramics composite material.

Further, test pieces corresponding to the surface layer 1 and the inner layer 11 of the silicon nitride ceramics composite material according to the present invention are prepared, and various sizes of flaws (sources of fracture) are previously formed on each test piece.
As a result of conducting a four-point bending strength test using
As shown in FIG. 8, it was found that the surface layer 1 has a large breaking strength against a small breaking source, and the inner layer 11 has a relatively large breaking strength against a large breaking source.

[0017]

As described above, the present invention relates to a composite material in which silicon nitride ceramics composed of silicon nitride particles and an oxynitride grain boundary phase containing silicon are laminated in a plurality of layers. Layers having different average particle sizes of silicon particles and different compositions of the oxynitride grain boundary phase are formed adjacent to each other, and the average particle size of the silicon nitride particles in the surface layer is set to the average particle size of the silicon nitride particles in the inner layer. By making it smaller than the size, a composite material having high strength and high toughness can be obtained.

Since the formation temperature of the grain boundary phase of each layer of the molded article is different, bonding between the layers can be facilitated.

Since the main component of the molded article is the same silicon nitride, there is no difference in thermal expansion between the layers, and no delamination due to thermal stress occurs.

A composite layer can be easily formed only by laminating and molding sheet-like molded bodies.

[Brief description of the drawings]

FIG. 1 is a side sectional view schematically showing a structure of a laminated silicon nitride ceramic composite material according to the present invention.

FIG. 2 is a side view schematically showing a laminating step for obtaining the silicon nitride ceramic composite material.

FIG. 3 is a plan sectional view schematically showing a structure of a surface layer of the silicon nitride ceramic composite material.

FIG. 4 is a plan sectional view schematically showing a structure of an inner layer of the silicon nitride ceramics composite material.

FIG. 5 is a diagram showing four-point bending strengths of the silicon nitride ceramics composite material according to the present invention and a conventional silicon nitride ceramics composite material.

FIG. 6 is a diagram showing the fracture toughness of a silicon nitride ceramics composite material according to the present invention and a conventional silicon nitride ceramics composite material.

FIG. 7 is a diagram showing the relationship between the magnitude of the fracture source and the fracture stress for the silicon nitride ceramic composite material according to the present invention and the conventional silicon nitride ceramic composite material.

FIG. 8 is a diagram showing the relationship between the size of the fracture source and the fracture stress for the surface layer and the inner layer of the silicon nitride ceramics composite material according to the present invention.

[Explanation of symbols]

1: Surface layer 2: Silicon nitride particles 3: Silicon nitride crystal phase 4: Grain boundary phase 5, 5a: Tantalum silicide 6: Iron silicide 11: Inner layer 12: Silicon nitride particles 14:
Grain boundary phase 16: iron silicide

Claims (3)

[Claims] 1. A composite material comprising silicon nitride ceramics composed of silicon nitride particles and an oxynitride grain boundary phase containing silicon laminated in a plurality of layers, wherein the silicon nitride particles have different average particle sizes. Further, layers having different compositions of the oxynitride grain boundary phase are formed adjacent to each other, and the average particle size of the silicon nitride particles in the surface layer is smaller than the average particle size of the silicon nitride particles in the inner layer. A laminated silicon nitride ceramic composite material. 2. The method according to claim 1, wherein the surface layer comprises silicon nitride particles, at least one of aluminum, yttrium, iron, and group 5 elements of the periodic table (long-period type) and a silicon oxynitride grain boundary phase.
A compound containing a group V element dispersed in part or all of the silicon nitride particles, a compound containing iron and silicon dispersed in the oxynitride grain boundary phase, and a group V dispersed in the oxynitride grain boundary phase The inner layer is composed of silicon nitride particles, an oxynitride grain boundary phase containing at least one of aluminum, yttrium, iron and magnesium, silicon and manganese oxide; The laminated silicon nitride ceramic composite material according to claim 1, wherein the laminated silicon nitride ceramic composite material is composed of iron and a compound containing silicon dispersed in a nitride grain boundary phase. 3. The laminated silicon nitride ceramic composite material according to claim 2, wherein said Group 5 element is tantalum.