JPH02204366A - Silicon nitride-based sintered body - Google Patents

Abstract

PURPOSE:To obtain the sintered body which is excellent in heat resistance, oxidation resistance, toughness and high-temp. strength without causing segregation of glass phase and sintering insufficiency by sintering a mixture consisting of both the mixed phase of silicon carbide-glass and beta-silicon nitride by ordinary pressure sintering-thermal isotropic pressure compression. CONSTITUTION:A silicon nitride-based sintered body is obtained by sintering a mixture incorporating both 20-30wt.% mixed phase of silicon carbide-glass which consists of 45-60wt.% silicon carbide and 40-55wt.% glass phase selected from alumina and oxide of rare earth elements and the balance beta-silicon nitride by ordinary pressure sintering-thermal isotropic pressure compression. Particle diameter of silicon carbide powder becoming a raw material is preferably regulated to 0.3-0.7mum. When the particle diameter of silicon carbide powder is made excessively small, the characteristics as the glass phase in the mixed phase of silicon carbide-glass are strongly exhibited and high-temp. strength is nonpreferably lowered. Further, when the particle size thereof is made excessively large, sintering is made insufficient and strength at ordinary temp. and high temp. is lowered. Further strength after thermal cycle wherein heating and cooling are repeated is nonpreferably lowered.

Description

[Detailed description of the invention] [Purpose of the invention]

(Industrial Application Field) The present invention relates to a silicon nitride sintered body that has excellent toughness and high-temperature strength, and has not only excellent heat resistance and oxidation resistance but also excellent toughness and high-temperature strength. Furthermore, the present invention relates to a silicon nitride sintered body of silicon carbide-glass-silicon nitride system which is suitably used as a material for various parts or products that are desired to be lightweight. (Conventional technology) In recent years, while the development of conventional metal-based materials is still progressing, the development of ceramic-based materials, which are considerably lighter than metal-based materials, is also progressing, such as alumina and zirconia. oxide-based materials, carbide-based materials such as silicon carbide, nitride-based materials such as silicon nitride, and composite-based materials such as silicon nitride-alumina have been developed, and some of them have been put into practical use. ing. Among these, in particular, silicon nitride sintered bodies are produced by hot isostatic pressing (H) after preliminary sintering of silicon nitride powder.
A method using sintering method (IP) (Japanese Patent Laid-Open No. 57
-71872 Publication) and ■Using a strengthening mechanism by crystallization of the glass phase +7) (K, H, Jack; 5cie
nce of Ceramics 11. P125
(1981), and (1) using a method of sintering a composite powder of silicon carbide and silicon nitride under hot isostatic pressure (Japanese Patent Application Laid-open No. 58-60673). There was such a thing. (Problems to be Solved by the Invention) However, in the conventional silicon nitride sintered bodies described above, the method in which silicon nitride powder is pre-sintered and then sintered by hot isostatic pressing is not suitable for glass. There are problems in that it is difficult to obtain high toughness due to phase segregation and insufficient sintering. There is a problem that the manufacturing process becomes complicated as it requires an annealing step for oxidation. Coarse grains and SiC
Although the addition of whiskers is effective in improving toughness, there are problems in that a large amount of glass phase is required and a preliminary sintering process using hot pressing is required in order to improve sinterability. It is desired to eliminate the various problems mentioned above. (Purpose of the Invention) This invention was made in view of the above-mentioned conventional problems, and does not cause segregation of the glass phase or insufficient sintering, does not make the manufacturing process too complicated, and has heat resistance. The object of the present invention is to provide a silicon nitride sintered body that not only has excellent toughness and oxidation resistance but also has excellent toughness and high-temperature strength.

[Structure of the invention]

(Means for Solving the Problems) The silicon nitride sintered body according to the present invention is silicon carbide-glass-silicon nitride-based, and contains 45 to 60% by weight of silicon carbide and alumina and rare earth oxides. The glass phase selected from the above contains 20 to 30% by weight of a silicon carbide φ glass mixed phase consisting of 40 to 55% by weight, and the remainder substantially consists of β-silicon nitride, and is produced by atmospheric pressure sintering and hot isostatic compression. It is characterized by having a structure formed by sintering one or more times,
The structure of such a silicon nitride sintered body is used as a means for solving the above-mentioned conventional problems. The silicon nitride sintered body according to the present invention has a silicon carbide content of 45 to
Part of the composition is a silicon carbide/glass mixed phase consisting of 60% by weight and 40 to 55% by weight of a glass phase selected from alumina and rare earth oxides, but the particle size of the silicon carbide powder that is the raw material in this case It is more desirable to use a silicon carbide powder with a particle size of 0.3 to 0.7 μm. In other words, if the particle size of the silicon carbide powder is too small, the characteristics of the lath phase in the silicon carbide-glass mixed phase will be stronger. On the other hand, if the particle size is too large, the sintering will be insufficient and the strength at room temperature and high temperature will be low, and it will be necessary to repeat heating and cooling. This is because the strength after thermocyclic treatment is also low, which is undesirable. In addition, as the glass phase, one or more oxides selected from alumina and rare earth oxides are used, and this glass phase accounts for 40% by weight in the silicon carbide/glass mixed phase. In other words, when silicon carbide is more than 60% by weight, the amount of silicon carbide in the silicon carbide/glass mixed phase increases, but the glass phase decreases inversely, making it difficult to sinter. This is not preferable because the strength and fracture toughness decrease during thermal cycling, and the strength after thermal cycling also decreases significantly.On the contrary, when the glass phase is more than 55% by weight in the silicon carbide/glass mixed phase, in other words, When the amount of silicon carbide is less than 45% by weight, the glass phase in the silicon carbide Φ glass mixture phase increases, making it easier to sinter, but the low amount of silicon carbide causes a decrease in high temperature strength and thermal cycle resistance. This is not preferable since the strength after use also decreases. The above silicon carbide ψ glass mixed phase is contained in the sintered body.
The balance of the sintered body is substantially composed of β-silicon nitride, but in this case, the amount of silicon carbide in the sintered body is less than 20% by weight of the glass mixed phase. When the amount of glass is low, the total glass mixed phase is small, which tends to cause insufficient sintering, resulting in a decrease in strength at room and high temperatures, as well as a decrease in strength after thermal cycling, and the fracture toughness value tends to be low. On the contrary, when the silicon carbide/glass mixed phase in the sintered body is more than 30 wt %, the amount of silicon carbide increases and sintering is inhibited.
This is not preferable because the strength and fracture toughness are reduced and the strength after thermal cycling is also reduced. The silicon nitride sintered body according to the present invention is obtained by first subjecting a mixed powder material to atmospheric pressure sintering, and then hot isostatic pressing.
ing). in this way. The silicon nitride sintered body according to the present invention is sintered at least twice. This is because the acicular β-silicon nitride grains and the silicon carbide/glass mixed phase are densely dispersed between the grains by performing pressureless sintering followed by hot isostatic compression. This is because a silicon nitride sintered body with high strength and high toughness can be obtained. (Function of the invention) The silicon nitride sintered body according to the present invention has the above-mentioned structure, uses a mixed phase of silicon carbide and a glass phase instead of the conventional glass phase, and By controlling the quantitative relationship between silicon carbide and glass phase components, and further controlling the quantitative relationship between the silicon carbide/glass mixed phase and β-silicon nitride, it is possible to achieve fairly dense sintering through liquid phase sintering under normal pressure. After obtaining a solid, silicon carbide, glass, and silicon nitride in the glass phase are solidified into a dense state by performing hot isostatic compression in which the partial pressure of N2, etc. is increased and pressure is uniformly applied at high temperature. Since it is made to be integrated, the main silicon nitride is dense acicular β-silicon nitride, and the acicular β
- Because the silicon carbide grains and glass phase are finely dispersed between the silicon nitride grains, it becomes a silicon nitride sintered body with high strength and toughness that cannot be obtained by multiple sintering. ing. (Example) Examples 1, 2, 3. Proportions 1, 2.3 Glass phase components include 5 parts by weight of yttrium oxide (Y2O2) powder, 5 parts by weight of alumina (AlI303) powder, and 2 particle sizes of 0.1 (Comparative Example 1) and 0.3 (Example 1). ), 0
．． Silicon carbide (S i
C) 20 parts by weight of each 5iC-glass mixed phase component consisting of 10 parts by weight of powder and β-silicon nitride (S i3 N4)
80 parts by weight of powder were mixed in a ball mill for 96 hours, air-dried, and then spray-dried, and then molded into a 30 x 40 x 30 mm compact by cold isostatic pressing (CIP) at a molding pressure of 4 tons. Next, pressureless sintering was performed using the sintering pattern shown in FIG. 1, followed by hot isostatic compression using the sintering pattern shown in FIG. 2. Next, the density ratio of each obtained sintered body [(sintered body density /
Theoretical density) xioo c%)] was measured, and a test piece of 4 x 3 x 3 Bmm was cut out from each sintered body, and a JIS
Based on R1601 (bending test performed at room temperature and 12
The bending strength at 00°C was measured, and the oxidized M? ! In addition, as a simulation test of the thermal history of automobile engine parts, we conducted a thermocyclic test using heating and air cooling at room temperature of 0800°C, measured the bending strength, and after mirror-polishing each specimen, we determined the hardness. and fracture toughness (Krc) were investigated. These results are shown in Table 1. As shown in Table 1, the particle size of SiC is 0.3 to 0.71.
In Examples 1 to 3 in which Lm is within the range, dense and acicular β-3i3N is obtained, and the SiC/glass mixed phase is densely dispersed between the particles, so that the temperature at room temperature The bending strength at high temperatures was high, the fracture toughness and the bending strength after the thermocyclic test were also high (4), and the hardness was also high. On the other hand, in the case of Comparative Example 1, in which the SiC particle size is as small as O, l pm, there are more fine particles in the 5iCe glass mixed phase, so the characteristics as a glass phase are stronger, and the high-temperature strength is increased. It was observed that the weight gain by oxidation was lower and the weight gain due to oxidation was higher compared to the others. Moreover, the SiC particle size is 1.0 pm and 2.0 pm. In the case of Comparative Examples 2 and 3, which have a large OJLm, the sintering is insufficient, so the strength at room temperature and high temperature is low, and the bending strength after the thermocyclic test is also low. It was found that when the SiC particle size was too large, the hardness was also low. Examples 4 and 5. Comparative Examples 4, 5, 6, 7.8 SiC/glass mixed phase consisting of 5 parts by weight of yttrium oxide powder, 5 parts by weight of alumina powder, and 10 parts by weight of silicon carbide powder with a grain size of 0.3 pm as glass phase components. The ingredients were 10 (Comparative Example 4), 15 (Comparative Example 5), 20 (Example 1 and Comparative Example 8), 25 (Example 4), 30 (Example 5), 35 (Comparative Example 6) and 40 (Comparative Example 7) Parts by weight of β-silicon nitride powder were 90 (Comparative Example 4), 85 (Comparative Example 5), and 80 (
Example 1 and Comparative Example 8), 75 (Example 4), 70 (
Example 5) Parts by weight of 65 (Comparative Example 6) and 60 (Comparative Example 7) were mixed in a ball mill for 96 hours, air-dried, further spray-dried, and then subjected to cold isostatic compression (CI P). ) with a molding pressure of 4 tons to 30X40
It was molded into a molded body with a size of 30 mm. Next, after pressureless sintering was performed using the sintering pattern shown in Figure 1, heat f
It was sintered by performing f11 isostatic compression. Next, the density ratio [(sintered body density/theoretical density) x 100 (%) J of each obtained sintered body was measured, and a test piece of 4 x 3 x 311 nm was cut out from each sintered body and JI
Based on S R1601, a bending test was conducted to measure the bending strength, and the oxidation weight gain was examined by holding the product in air at 1000℃ for 100 hours.Furthermore, as a simulated test of the thermal history of automobile engine parts, the material was heated from room temperature to 800℃. A thermal cyclic test was conducted to measure the subsequent bending strength, and each specimen was mirror-polished and its hardness and fracture toughness (KIC) were examined. These results are shown in Table 2. As shown in Table 2, in Examples (1) and 4.5, in which the SiCφ glass mixed phase in the sintered body was in the range of 20 to 30% by weight and was sintered twice, the SiCφ glass mixed phase was dense and acicular. β-5i3
Since N4 is obtained and the 5iC-glass mixed phase is densely dispersed between its grains, it has high bending strength at room temperature and high temperature, and has excellent fracture toughness and bending strength after thermocyclic tests. It also showed a high value, and the hardness also showed a high value. On the other hand, the 5iC-glass mixed phase in the sintered body is 10
In the case of Comparative Examples 4 and 5, which have a small amount of 15% by weight, the total amount of the two glass phases is small, which tends to result in poor sintering, so the bending strength at room temperature and high temperature is low, and the flexural strength after the thermocyclic test is low. The bending strength was also low, and the fracture toughness was also low. In addition, in the case of Comparative Examples 6 and 7, where the SiC*glass mixed phase is large at 35% by weight and 40% by weight, although the total glass phase is large, the amount of SiC is also large, and sintering is inhibited. Therefore, it was observed that the strength and fracture toughness at room temperature, high temperature, and after ripening were low, and the hardness was also low. Furthermore, in the case of Comparative Example 8, in which only pressureless sintering was performed with the sintering pattern shown in Fig. 7tS1, and the second sintering was not performed, sintering mainly consisting of dense acicular β-5j3N was performed. It was observed that the strength and fracture toughness were low, especially after high temperature and thermocyclic cycles, because the steel was unable to obtain a solid body. Example 6.7. Comparative Examples 9, 10, 11.12 Using equal amounts of yttrium oxide and alumina as glass phase components and using silicon carbide powder with a particle size of 0.3 pm, the amount of silicon carbide relative to the total amount of the glass phase components and silicon carbide was The ratio of the amount was 30 (Comparative Example 9), 40 (Comparative Example 10), 45 (Example 6), 50 (Example 1), 60 (Example 7), 65 (
Comparative Example 11) and 70 (Comparative Example 12) Using raw material powders of silicon carbide-glass mixed phase with a weight percent of 70% by weight, 20 overlapping parts of each silicon carbide-glass mixed phase powder and 80 weight% of β-silicon nitride powder were used. 96 hours each in a ball mill.
Mix. After air drying, spray drying was performed, and then cold isostatic pressing (CI P) was performed at 30X at a molding pressure of 4 tons.
It was molded into a molded body of 40 x 30 mm. Next, pressureless sintering was performed using the sintering pattern shown in FIG. rJS1, followed by hot isostatic compression using the sintering pattern shown in FIG. Next, the density ratio [(sintered body density/theoretical density) xioo (%) of each obtained sintered body was measured, and a test piece of 4 x 3 x 36 mm was cut out from each sintered body, and a JIS
We conducted a bending test based on R1601 to measure the bending strength, and also held it in air at 1000°C for 100 hours to examine the increase in fermentation.Furthermore, as a simulation test of the thermal history of automobile engine parts, we conducted a heat test at room temperature H800°C. A cyclic test was conducted to measure the subsequent bending strength, and each specimen was mirror polished and then examined for hardness and fracture toughness (KIC). These results are shown in Table 3. As shown in Table 3, SiC in the SiC/glass mixed phase
Example 6, where the amount is in the range 45-60% by weight. (1),
In No. 7, dense and acicular β-3i3N4 is obtained, and the SiC/glass mixed phase is densely dispersed between the grains, so it has high bending strength at room temperature and high temperature. The fracture toughness and bending strength after the thermocyclic test also showed high values, and the hardness also showed high values. On the other hand, the amount of SiC in the SiC*glass mixed phase is 3
In the case of Comparative Examples 9 and 10, which are small at 0% by weight and 40% by weight, 5iC (as the amount of i is small and the amount of glass phase increases, it is easy to sinter, but the high temperature strength decreases, It was observed that the influence on the bending strength after thermocyclic was large and the value was low, and the hardness was also low.In addition, the amount of SiC in the SIC/glass mixed phase was 65 gf. ,
Comparative Example 11 and Comparative Example 1 with large amounts of % and 70% by weight
In the case of No. 2, as Si CFJ increases and the glass phase decreases, it becomes difficult to sinter, and it was observed that the strength did not increase and at the same time the fracture toughness and hardness became inferior. As shown in the above examples, in the silicon nitride sintered body according to the present invention, the SIC grain size is regulated, the quantitative relationship between SiC and the glass phase is regulated, and the total amount of SiC and the glass phase is regulated. However, after obtaining a fairly dense sintered body through liquid-phase sintering using pressureless sintering, we performed hot isostatic compression in which the N2 partial pressure was increased and sintered by uniformly pressurizing at a higher temperature. By closely solidifying and integrating silicon carbide, glass, and silicon nitride in the glass phase, silicon nitride has excellent heat and oxidation resistance, room temperature and high temperature strength, and fracture toughness, and is also highly hard. It is a sintered body. [Effect of the invention] The silicon nitride sintered body according to the present invention has a silicon carbide content of 45 to
60% by weight and 40% to 55% by weight of a glass phase selected from alumina and rare earth oxides. Pressure sintering - Since it has a structure that is sintered by hot isostatic pressing, it does not cause segregation of the glass phase or insufficient sintering, and the process does not become very complicated. , we can provide a silicon nitride sintered body that has outstanding heat resistance and oxidation resistance, as well as excellent toughness and high-temperature strength, and also has high hardness and wear resistance. , oxidation resistance,
It is suitable for use as a material for various parts or products that require excellent properties such as toughness, high-temperature strength, and wear resistance, and can also reduce the weight of these parts or products. This brings about an extremely excellent effect.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the sintering pattern adopted in the pressureless sintering in the examples and comparative examples of the present invention, and Fig. 2 is an explanatory diagram showing the sintering pattern similarly adopted in the hot isostatic pressing. be. z t('c) L(OC)

Claims (1)

[Claims] (1) 45-60% by weight of silicon carbide and 40-55% by weight of a glass phase selected from alumina and rare earth oxides
20 to 30% by weight of a silicon carbide/glass mixed phase consisting of 20% to 30% by weight, the remainder substantially consisting of β-silicon nitride, and is sintered by pressureless sintering and hot isostatic compression. Silicon-glass-silicon nitride based silicon nitride sintered body.