JPH0524924A - Sic-coated silicon nitride-silicon carbide combined sintered compact - Google Patents

Abstract

(57) [Summary] [Constitution] The weight ratio of SiC / (SiC + Si ₃ N ₄ ) is 0.
A SiC-coated silicon nitride-silicon carbide composite sintered body, characterized in that a Si ₃ N ₄ -SiC composite sintered body of 1 to 0.5 is coated with SiC having a film thickness of 2 to 100 μm. [Effect] A coating which is coated with a SiC film having excellent adhesion, which is resistant to strength deterioration due to the coating of SiC, peeling of the coating film when used under a thermal cycle, and strength deterioration, and which has oxidation resistance and wear resistance. A sintered body can be obtained.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention requires structural materials which are used at high temperatures, such as gas turbine parts and automobile engine parts, and which have oxidation resistant and heat resistant cycles, and high hardness and wear resistance of cutting tools, sliding members and the like. Related to the material.

[0002]

2. Description of the Related Art The following are coated sintered bodies in which the adhesion between SiC (covering material) and the sintered body is improved. JP-A-58
Japanese Patent Laid-Open No. 88190 discloses a coated sintered body in which a silicon nitride (Si ₃ N ₄ ) sintered body is CVD coated with silicon carbide (SiC) (hereinafter referred to as “prior art 1”). In Japanese Patent Laid-Open No. 62-197370, a crystal phase having a large coefficient of thermal expansion is precipitated at a grain boundary of a silicon nitride (Si ₃ N ₄ ) sintered body to bring it closer to the coefficient of thermal expansion of a silicon carbide (SiC) coating. A coated sintered body having improved adhesion strength is disclosed (hereinafter referred to as "prior art 2").

[0003]

However, these conventional SiC-coated Si ₃ N ₄ sintered bodies have the following problems. The coated sintered body according to the conventional technique 1 has a difference in thermal expansion between the sintered body (Si ₃ N ₄ ) and the coating material (SiC).
Cracks will occur when used under heat cycle. Coated sintered body according to the prior art 2, Si ₃ in order to approximate the thermal expansion coefficient of Si ₃ N ₄ sintered body in thermal expansion coefficient of SiC
A large amount of sintering aid used during the sintering of N ₄ causes the strength of the sintered body to deteriorate. For the above reasons, the coated sintered body of the prior art cannot be used under the environment where the thermal cycle required when used as a structural material is applied. An object of the present invention is to prevent the deterioration of strength due to the coating of SiC and the peeling and strength deterioration of the coating film when used under a thermal cycle, and the oxidation resistance and wear resistance of the SiC film coated with excellent adhesiveness. To provide a coated sintered body having:

[0004]

Means for Solving the Problems The means is SiC /
(SiC + Si ₃ N ₄ ) Si with a weight ratio of 0.1 to 0.5
_The film thickness is 2 to 100 μm on the ₃ N ₄ —SiC composite sintered body.
SiC of is to use a SiC coated Si ₃ N ₄ -SiC composite sintered body characterized by being coated. Here, as a method of coating the SiC film, carbon source gas and S
A CVD method (for example, plasma CVD method, thermal CVD method) in which a gas obtained by exciting a mixed gas of i source gas is brought into contact with a sintered body.
Coating method, photo CVD method) or PVD method, but the CVD method is most preferable from the viewpoint of throwing power. Further, the sintered body may be obtained by any method such as normal pressure sintering, hot press sintering, gas pressure sintering, and HIP sintering.

[0005]

The sintered body used in the present invention is SiC / (SiC +
Si ₃ N ₄ -with a weight ratio of Si ₃ N _{4 of} 0.1 to 0.5.
Since it is a composite sintered body of SiC, the coefficient of thermal expansion is close to the coefficient of thermal expansion of the SiC film, and there is little peeling of the film or deterioration of the strength of the coated sintered body due to residual stress acting on the interface between the film and the sintered body. Also, Si ₃
Since a sintered body that has been made stronger by combining SiC with N ₄ is used, there is no strength deterioration that occurs when a large amount of a sintering additive is added to adjust the thermal expansion coefficient to SiC. .. Further, when synthesizing the SiC film, the SiC uniformly dispersed in the sintered body is placed in an environment where a heat cycle is applied in order to enhance the adhesion between the sintered body and the film in the process of vapor phase synthesis. However, the film does not peel off. When the SiC / (SiC + Si ₃ N ₄ ) weight ratio of the sintered body is less than 0.1, the difference between the coefficient of thermal expansion of the sintered body and the coefficient of thermal expansion of the film becomes large, so that the film / sintered The film is likely to peel off due to the residual stress at the body interface, and the adhesion of the film is also reduced due to the small amount of SiC in the sintered body. Therefore, when used in an environment where a thermal cycle is applied, the film tends to peel off. On the contrary, when the SiC / (SiC + Si ₃ N ₄ ) weight ratio of the sintered body becomes larger than 0.5, the property of the sintered body itself becomes close to that of SiC and becomes weak against thermal shock, so that the strength deterioration after the thermal cycle is caused. It can grow.

When the film thickness of SiC is less than 2 μm,
The effect of improving the oxidation resistance by the film is insufficient, 100 μm
If it exceeds, the strength of the coated sintered body is deteriorated or the film adhesiveness is deteriorated due to residual stress accumulated in the film beyond the effect of improving the film adhesiveness by SiC in the sintered body. Si
_For the production of the ₃ N ₄ —SiC composite sintered body, S was used as the starting material.
When an amorphous powder containing i, C and N is used, better adhesion can be obtained than when a crystalline powder of Si ₃ N ₄ or SiC is used as a starting material. When an amorphous powder containing Si, C and N is used as a starting material, SiC is contained in the sintered body.
It is considered that this is because the particles are easily dispersed uniformly and finely, and the effect of SiC in the sintered body on the film adhesion is further enhanced.

The composition of the SiC film is based on the composition ratio of the source gas (Si
Source gas / carbon source gas molar ratio) 0.5 to 2.0, synthesis pressure 100 to 400 torr Synthesis temperature 1200 to 1400 ° C
It is preferable to carry out. If the source gas composition ratio and the synthesis pressure deviate from this range, the effect of the presence of SiC in the sintered body does not sufficiently appear, the compatibility between the sintering and the film is poor, and micropores are generated in the film to prevent the acid resistance of the film. There is a case where the chemical conversion becomes worse. When the synthesis temperature is less than 1200 ° C, amorphous is remarkably formed in the film, and when it exceeds 1400 ° C, pores are formed in the film and the oxidation resistance is lowered in any case.

EXAMPLES Amorphous powder containing Si, C and N as a starting material for a base material (indicated as Si—C—N in the table) is mixed with Y ₂ O ₃
8% by weight of powder was added, wet-mixed, dried, and hot-press sintered (pressure 350 kgf / cm ² , temperature 1800).
Various SiC / (SiC + Si ₃₎
A sintered body having a N ₄ ) weight ratio was produced. In addition, as a starting material for the base material, Si ₃ N ₄ powder (specific surface area 10 m ² / g), S
iC powder (specific surface area 17 m ² / g) and Y ₂ O ₃ powder 8% by weight were wet mixed, dried, and then hot-press sintered (pressure 350 kgf / cm ² , temperature 1800 ° C., time 4 h) to perform various types of SiC. A sintered body having a weight ratio of / (SiC + Si ₃ N ₄ ) was prepared.

[Table 1] The obtained sintered body was subjected to surface grinding with a # 200 DIAMIND grindstone, and then placed in a reaction container of a thermal CVD apparatus. Then, under the conditions of the synthesis temperature and the synthesis pressure shown in Table 1, the raw material gases SiCl ₄ and CH ₄ were introduced into the reaction chamber at the SiCl ₄ / CH ₄ ratio shown in Table 1, and the hydrogen gas was 2.0 S.
Introduced by LM and Si with a thickness of 1 to 150 μm on the sintered body
C film was coated.

Then, for these samples, the span 30
3-point bending strength test in mm, 1400 ° C in air
After the oxidation test for 200 hours, the oxidation weight increase measurement and the thermal cycle from room temperature to 1400 ° C in the atmosphere were performed for 10 times.
Visual inspection of film adhesion and span 30 after applying 0 times
Table 2 shows the results of the three-point bending strength test of mm. Here, the oxidation weight increase is defined as (weight after oxidation test-weight before oxidation test) / (front surface area).

[Table 2] The embodiment according to the present invention is No. 1-No. No. 10, and the comparative example is No. 11-No. Sixteen. Si ₃
When the N ₄ -SiC composite sintered body is used alone as the base material (No. 14), the base material has poor oxidation resistance, so that strength deterioration easily occurs when used at high temperatures. In many cases, the various SiC-coated base materials shown in (1) have a remarkable effect of improving the oxidation resistance. Coated sintered body using Si ₃ N ₄ (No. 11) and Si with low SiC content
Coated sintered body using ₃ N ₄ -SiC composite sintered body (N
o. In 12), peeling of the film occurs after the heat cycle test. No. 11 and No. In No. 12, since the difference in the coefficient of thermal expansion between the film and the sintered body is large, a large residual stress is generated at the film / sintered body interface, and there is no (or little) effect of improving the film adhesion by SiC in the sintered body. Therefore, it is considered that the film peeled off during the thermal cycle.

On the other hand, SiC is replaced by SiC / (SiC + Si ₃
N ₄ ) 0.1 to 0.5 composite by weight ratio of sintered body No.
In Nos. 1 to 10, no peeling of the film occurred even after 100 thermal cycles. No. No. 1 among 10 No. 1 has a relatively large coefficient of thermal expansion between the SiC film and the sintered body, and it is considered that the film is easily peeled off. However, since SiC uniformly dispersed in the sintered body contributes to the improvement of the film adhesion. It is considered that peeling is less likely to occur. SiC / (SiC + S
When a sintered body having a weight ratio of i ₃ N ₄ ) of more than 0.5 was used (No. 13), it is considered that the sintered body itself was weak against thermal shock, so that the strength deterioration after the thermal cycle was large. Be done. Considering the strength before and after the heat cycle, the example No. 1 and N
o. 4, the SiC / (SiC + Si ₃ N ₄ ) weight ratio is more preferably 0.2 to 0.4.

No. 1 having a film thickness of 1 μm Sample No. 15 has a large oxidation increase in the oxidation test and is considered to have an insufficient film thickness. No. with a film thickness of 150 μm It is considered that in No. 16, film peeling occurred after the heat cycle test, and the residual stress accumulated in the film became larger than the effect of enhancing the film adhesion of SiC in the sintered body because the film was thick. Also, sample N
o. 1-No. When the SiC of the coating film of 10 was analyzed by X-ray, the β phase was mainly confirmed.

As described above, according to the present invention, an SiC coated member having good oxidation resistance and little strength deterioration can be obtained, and industrially useful effects such as being able to be used in an environment where a heat cycle is applied in practical use are obtained. You can get it.

Claims (1)

To the Claims 1] _{SiC / (SiC + Si 3 N} 4) weight ratio on Si ₃ N ₄ -SiC composite sintered body of 0.1 to 0.5,
A SiC-coated silicon nitride-silicon carbide composite sintered body, which is coated with SiC having a film thickness of 2 to 100 μm. [0001]