JP2699697B2 - Method for producing silicon carbide / silicon nitride composite sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

This invention relates to high-temperature strength, heat resistance,
It is used as a material for parts or products that are required to have excellent corrosion resistance and the like, and is used, for example, to produce a silicon carbide / silicon nitride composite sintered body that is suitably used as a material for automobile engine parts. And a method for producing a silicon carbide / silicon nitride composite sintered body.

[0002]

2. Description of the Related Art Silicon carbide (SiC) and silicon nitride (Si ₃
As a conventional composite sintered body mainly composed of N ₄ ), for example, 10 to 72% by volume SiC and 5 to 65% by volume Si ₃ N
_A composite sintered body composed of ₄ and 5 to 40% by volume of Si (Japanese Patent Application Laid-Open No. 61-36176), or a rare earth oxide mainly composed of SiC and Si ₃ N ₄ and 0.05 to 50% by weight is added. to sintered composite sintered body (JP 60-46973 JP) and, SiC and Si ₃ mixed powder periodic table II with N _4, III, IV metals and acid-carbide (See Japanese Patent Application Laid-Open No. 58-9107)
No. 0) is disclosed in the Japanese Patent Publication.

[0003] In addition, Journal of Ame
rican Ceramic Society 56
In (9) 445 (1973), Lange, and in 63 (9-10) 597 (1980), Greskovich reported mechanical properties of a silicon carbide / silicon nitride composite sintered body.

[0004] There is also a composite sintered body (JP-A-1-275470) in which a mixed powder is prepared from an organosilicon compound by a gas phase method and then hot-pressed.

[0005] Further, as a product manufactured by normal pressure sintering, a composite sintered body in which silicon nitride is composed of a needle-like β phase, silicon carbide is a single crystal and the particle diameter is 2 to 30 µm ( JP-A-64-9872).

[0006]

However, most of the conventional methods for producing a silicon carbide / silicon nitride composite sintered body employ a hot press in order to promote densification during sintering. Because of the necessity, it has been a problem that it is difficult to manufacture parts or products having complicated shapes.

Further, since the composite sintered body cited at the end uses normal pressure sintering, it is possible to manufacture a part having a complicated shape and to have an excellent toughness value. There has been a problem that the strength may be inferior.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and it is possible to obtain a ceramic part or product of a complicated shape without using hot pressing. It is an object of the present invention to provide a method for producing a silicon carbide / silicon nitride composite sintered body that can be used as a ceramic part or product having higher strength and impact value than a normal pressure sintered product.

[0009]

According to the present invention, there is provided a method of manufacturing a silicon carbide / silicon nitride composite sintered body, comprising: mixing a mixed powder mainly composed of β-type silicon carbide powder and α-type silicon nitride powder with a pressure of more than 1 atm. After gas pressure sintering (primary sintering) at 5 atm or less, resintering (secondary sintering) at a temperature 100 to 200 ° C. higher than the gas pressure sintering temperature and under a nitrogen partial pressure of 10 to 2000 atm. The present invention relates to such a method for producing a silicon carbide / silicon nitride composite sintered body, and is a means for solving the above-described conventional problems.

When a sintered body mainly composed of silicon nitride is toughened, other component particles larger than the silicon nitride particles, such as silicon carbide particles, are mixed to complicate the fracture path. In some cases, a technique for improving the toughness value has been adopted.

However, in this case, since large component particles are mixed, the size of the fracture source is increased, which may cause a decrease in strength, and the effect of improving the toughness value may not be fully utilized. Was.

On the other hand, when component particles smaller than the silicon nitride particles are mixed, they are segregated at the grain boundaries, and the improvement in fracture toughness and strength is small.

Therefore, in the present invention, the composite material in which silicon carbide is segregated at the grain boundaries is subjected to gas pressure sintering (primary sintering) at a pressure exceeding 1 atm to 5 atm and then resintering (secondary sintering) Sintering).

At this time, when the primary sintering is performed with the pressure in gas pressure sintering exceeding 5 atm, 3SiC + 2N ₂ → S
It has been found that a chemical reaction of i ₃ N ₄ + 3C occurs, and SiC in the powder reacts with the nitrogen gas to generate silicon nitride and carbon, which hinders sintering, which is not preferable.

The resintering temperature after the gas pressure sintering is 100 to 200 ° C. higher than the gas pressure sintering temperature, and the partial pressure of nitrogen is reduced to 10 atm to prevent decomposition of silicon nitride. Various experiments have confirmed that it is necessary to make the above, and it is better to set the nitrogen partial pressure during resintering to 10 to 2000 atm.

The silicon carbide / silicon nitride based composite sintered body produced here contains 5 to 15% by volume of β-type silicon carbide, and the remainder is added with β-type silicon nitride and other appropriate sintering aids. It is particularly desirable to be made of a grain boundary glass phase produced by the above method.

It is desirable that the β-type silicon carbide powder used in the present invention has a particle diameter of about 0.2 to 0.5 μm.

[0018]

The method for manufacturing a silicon carbide / silicon nitride composite sintered body according to the present invention is characterized in that a mixed powder mainly composed of a β-type silicon carbide powder and an α-type silicon nitride powder is mixed in a pressure exceeding 1 atm to 5 atm or less. The sintered body obtained by performing gas pressure sintering (primary sintering) between 100 and 100 ° C. above the gas pressure sintering temperature (primary sintering temperature)
Since resintering (secondary sintering) is performed at a high temperature of 200 ° C. and under a partial pressure of nitrogen of 10 to 2,000 atm, the produced silicon carbide / silicon nitride composite sintered body is gas-pressure sintered. The subsequent re-sintering causes the growth of the silicon nitride particles as the matrix, so that β-type silicon nitride particles
It has a structure in which silicon carbide particles are incorporated, and has high strength and low hardness.Since silicon carbide particles in silicon nitride particles can easily absorb load, Since cracks are generated around the silicon particles due to a difference in thermal expansion coefficient and plastic deformation is likely to occur due to a point load, the impact is absorbed to obtain a high toughness.

[0019]

【Example】

(Examples 1, 2, 3) As shown in Table 1, α-Si ₃ N
Powder consisting of 85% by weight of ₄ and 10% by weight of Y ₂ O ₃ and 5% by weight of Al ₂ O ₃ as sintering aids: 95,9
0.85% by volume and β-Si having a particle diameter of 0.3 μm
C powder: 5, 10 and 15% by volume were mixed in a ball mill in ethanol, and the mixed powder obtained by drying was molded by cold isostatic pressing (CIP; compression pressure 4 ton / cm ² ). First sintering (gas pressure sintering) at 1750 ° C. for 3 hours in a 2 atm N ₂ gas atmosphere,
Further, in an N ₂ gas atmosphere at 1000 atm.
By performing secondary sintering (re-sintering) at 0 ° C. for 1 hour, each composite sintered body of Examples 1, 2, and 3 was obtained. FIGS. 1 and 2 show changes in the primary sintering and secondary sintering temperatures and atmospheric pressures at this time.

Next, when the density of each of the obtained sintered bodies was examined, the results are as shown in the columns of Examples 1, 2 and 3 in Table 3, and the density was 3.27 to 3 It showed a large value of .29 g / cm ³ .

When the crystal phase of each sintered body was examined,
As shown in Table 3, all of β-SiC and β-Si ₃ N ₄
Was the subject.

Further, the bending strength (σf), fracture toughness (k _IC ), hardness (Hv) and impact resistance (Vc) of each sintered body were examined. The results are shown in each column of No. 3.

At this time, the bending strength was measured by a bending strength test by JIS four-point bending, the fracture toughness value was measured by an indentation method, the hardness was measured by a Vickers hardness tester, and the impact resistance was 1.0 mm in diameter. The results are shown by measuring the speed (Vc) at which zirconia particles are injected to reduce the strength. The impact resistance is about 300 m / s or more. It is desirable.

As shown in the columns of Examples 1, 2 and 3 in Table 3, it was recognized that the bending strength, fracture toughness, hardness and impact resistance of each sintered body were all good. Thus, it was inferred that such improvement in properties resulted in an improvement in both strength and impact resistance due to the effect of the fracture toughness value on the strength and the effect of the silicon carbide particles in the silicon nitride particles absorbing the load.

(Examples 4 and 5) As shown in Table 1, a mixed powder obtained by mixing 10% by volume of β-SiC powder was cold isostatically pressed (CIP; compression pressure 4 ton / c) as in Example 2.
m ² ), then pressurize at 1 and 5 atm N ₂
The primary sintering was performed at 1750 ° C. for 3 hours in a gas atmosphere, and the secondary sintering was performed at 1850 ° C. for 1 hour in a N ₂ gas atmosphere at 1000 atm. I got

Next, when the density of each of the obtained sintered bodies was examined, the results were as shown in each column of Examples 4 and 5 in Table 3, and the density was 3.29 to 3.30 g. / Cm ³ , which was a large value.

When the crystal phase of each sintered body was examined,
As shown in Table 3, all of β-SiC and β-Si ₃ N ₄
Was the subject.

Further, the bending strength (σf), fracture toughness (k _IC ), hardness (Hv), and impact resistance of each sintered body were examined. The results are shown, and it was confirmed that all of them were good.

(Examples 6, 7, 8) As shown in Tables 1 and 2, a mixed powder obtained by mixing 10% by volume of β-SiC powder was cold isostatically pressed (CIP; compressed) as in Example 2. After molding at a pressure of 4 ton / cm ² ), pressurize at 2 atm N
Primary sintering is performed at 1750 ° C. for 3 hours in a _two- gas atmosphere, and N,
By performing secondary sintering at 1850 ° C. for 1 hour in a _two- gas atmosphere, composite sintered bodies of Examples 6, 7, and 8 were obtained.

Next, when the density of each of the obtained sintered bodies was examined, the results were as shown in the columns of Examples 6, 7, and 8 in Tables 3 and 4, and the density was 3. 28-3.29 g
/ Cm ³ , which was a large value.

When the crystal phase of each sintered body was examined,
As shown in Tables 3 and 4, both β-SiC and β-SiC
The main component was Si ₃ N ₄ .

Further, when the bending strength (σf), fracture toughness value (k _IC ), hardness (Hv) and impact resistance of each sintered body were examined, Examples 6, 7 and The results are shown in each column of No. 8, and it was recognized that all of them were good.

(Reference Examples 1 and 2) As shown in Table 2, the mixing ratio of β-SiC powder in Examples 1, 2 and 3 was changed to 3% by volume and 20% by volume. , 3
Each sintered body having a β-SiC phase and a β-Si ₃ N ₄ phase was obtained by performing primary sintering and secondary sintering in the same manner as described above, and the same test was performed.

As shown in the columns of Reference Examples 1 and 2 in Table 4, β
In the case of Reference Example 1 having a low -SiC content, β-Si
Since the effect of adding C was not sufficiently obtained, the flexural strength, fracture toughness and impact resistance were all inferior, and in the case of Reference Example 2 having a large β-SiC content, the flexural strength and fracture Although the toughness value was good, the impact resistance tended to decrease.

Therefore, 5-1 is contained in β-Si ₃ N _4.
It has been found that it is particularly preferable to include 5% by volume of β-SiC.

(Comparative Example 1) As is apparent from a comparison between Example 2 in Table 1 and Comparative Example 1 in Table 2, in Comparative Example 1, the N ₂ atmosphere pressure during primary sintering was 9 atm. A sintered body was obtained by the same process as in Example 2 except that the height was increased.

In the sintered body thus obtained, the reaction between SiC and N ₂ occurs because the atmospheric pressure during the primary sintering is too high, and Si ₃ N ₄ and C (carbon) are generated. To prevent the primary sintering, thereby hindering the subsequent densification during the secondary sintering. As shown in the column of Comparative Example 1 in Table 4, the density is low and the strength and impact resistance are reduced. Both had decreased.

(Comparative Example 2) As is clear from comparison between Example 2 in Table 1 and Comparative Example 2 in Table 2, in Comparative Example 2, the N ₂ atmosphere pressure during the secondary sintering was 5 atm. A sintered body was obtained by the same steps as in Example 2 except that the temperature was lowered.

In the sintered body thus obtained, the atmosphere pressure during the secondary sintering is too low, which tends to cause the decomposition of silicon nitride. Although the density of the sintered body is improved, the bending strength and the impact The resistance was also reduced.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

[Table 4]

[0044]

According to the method for producing a silicon carbide / silicon nitride composite sintered body according to the present invention, a mixed powder mainly composed of a β-type silicon carbide powder and an α-type silicon nitride powder is mixed at a pressure exceeding 1 atm to 5 atm or less. After gas pressure sintering, between 10 and 10
Since the resintering is performed at a high temperature of 0 to 200 ° C. and under a partial pressure of nitrogen of 10 to 2,000 atm, the microstructure during normal pressure (primary) sintering is smaller than that produced by only normal pressure sintering. Sintering more densely and performing grain growth at the time of re-sintering (secondary) sintering by secondary sintering more uniformly can realize higher strength, and can achieve high strength and It can provide fine ceramics with excellent impact resistance, and in gas pressure sintering, the characteristic value has a peak at atmospheric pressure between more than 1 atm and 5 atm or less, so strict pressure control is unnecessary, It is possible to cope with non-uniform pressure in the furnace, and at the same time, it is possible to produce a large number of ceramic parts or products.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing patterns of changes in temperature and N ₂ gas ambient pressure during gas pressure sintering employed in Examples 1, 2, and 3 of the present invention.

FIG. 2 is an explanatory diagram showing a pattern of changes in temperature and N ₂ gas atmosphere pressure during re-sintering employed in Examples 1, 2, 3 of the present invention.

Claims (2)

(57) [Claims] 1. A gas mixture comprising a mixed powder mainly composed of β-type silicon carbide powder and α-type silicon nitride powder, which is subjected to gas pressure sintering at a pressure of more than 1 atm to 5 atm or less, and 100 to 200 ° C.
A method for producing a silicon carbide / silicon nitride composite sintered body, wherein resintering is performed at a high temperature under a partial pressure of nitrogen of 10 to 2000 atm. 2. The manufactured silicon carbide / silicon nitride composite sintered body contains 5 to 15% by volume of β-type silicon carbide, and the balance is mainly composed of β-type silicon nitride. The method for producing a silicon carbide / silicon nitride composite sintered body according to the above.