JPS605074A - Silicon carbide sintered body and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention relates to a silicon carbide sintered body and a method for manufacturing the same.

Silicon carbide sintered body has excellent oxidation resistance, thermal shock resistance,
Due to its corrosion resistance and high-temperature strength, it has been widely used in various fireproof materials, heating elements, abrasive materials, etc. When used for these purposes, the presence of a considerable amount of pores in the sintered body does not pose much of a problem, and such sintered bodies are actually used.

However, in recent years, taking advantage of the above-mentioned features of silicon carbide sintered bodies, its uses have expanded to include various structural materials, check valves and sealing materials for corrosive liquids, heat exchange materials for high-temperature furnaces, and even strong wear-resistant members. As a result, there has been a demand for a sintered body with virtually no pores and greater strength.

Methods for producing silicon carbide bodies include (a) gas phase reaction method;
(b) Reactive sintered lumps and (1) hot sintering methods, but method (a) yields homogeneous and dense silicon carbide, but can usually only produce a thin film and is practically a coating of various materials. The method (b) is usually a method in which carbon and silicon or silicon dioxide powder are mixed and fired, and although it is possible to obtain objects with a large shape, it is difficult to obtain dense objects. It is only applied to the production of refractories and heating elements. Therefore, it can be said that the above method (c) is optimal for obtaining a thick (and dense) sintered body.

However, since silicon carbide is a compound with large covalent bonds, it is hard, tough, and stable even at high temperatures, so silicon carbide alone has extremely poor sintering properties, making it difficult to produce a sintered body that can be put to practical use. Since it is difficult to obtain such additives, research has been conducted into incorporating various sintering aids. For example, the report by Alliegro et al. (R, ^11-11-1e at, al, Jo
Urnal of Aw+erican Ceremi
cSocietg, 1956, vol. 39, 386-3
89P), JP-A No. 49-7311, JP-A No. 49-Sho.
-99308 publication, JP-A-50-78609 publication,
JP-A-51-65111, JP-A-53-8401
Publication No. 3, JP-A No. 53767711 and JP-A No. 5
2-6716, etc., AL, Fa, B, B,
It has been reported that if IC or the like is used as a sintering aid, a sintered body with fewer pores and greater strength can be obtained.

By the way, the strength of a sintered body is determined by various factors, but (a)
Porosity, (b) surface flaws, and (c) particle size have a large effect on the strength.

The surface scratches in (b) can be avoided by paying attention to processing.
Furthermore, the porosity (a) can be almost solved by using various sintering aids as described above to obtain a sintered body with very low porosity. However, the problem of particle size (c) is the most difficult, as grain growth occurs during sintering, making it difficult to obtain fine-grained sintered bodies (this is the reason why it is not possible to increase the strength above a certain limit). Regarding these facts, S. Prochazka et al.
, aram, Soc, Bull.

52885-891 (1973)) reported that crystal grains grow and their strength does not become very large.

The present invention aims to solve the above-mentioned problems and provide a silicon carbide sintered body with high density and fine grains and a method for manufacturing the same.
(b) Partially stabilized zirconium oxide 2 to 15% by weight, (b) 2 to 4% of partially stabilized zirconium oxide in which one or more of 1 to 4 mol% of ittria, 2 to 6 mol% of magnesia, and 2 to 7 mol% of calcia are dissolved.
A silicon carbide sintered body having a composition of 6% by weight and the balance being (c) silicon carbide, and (8) 5 to 15% by weight of erbium oxide powder, (b) 1 to 4 mol% of ittria, and 2 to 4% of magnesia.
6 mol %, 2 to 6 mol % of partially stabilized zirconium oxide powder in which one or more of 2 to 7 mol % of calcia is dissolved in solid solution, and the balance is (c) silicon carbide powder are mixed and then molded. This is a method for producing a silicon carbide sintered body, characterized in that sintering is performed by a hot sintering method.

The experiments and results that led to the present invention are shown below.

<Experiment I> SiC powder with a purity of 98.5% and an average particle size of 0.5 PIII, Z'02 powder with a purity of 99.9% and an average particle size of 5 pHl, and partially stabilized Zr as shown in Table 1 with a particle size of 5 m. 08
After mixing and pulverizing various types of powder in the proportions listed in Table 1 using a ball mill mixer,
This was thoroughly dried and used as a raw material for sintering, and 50X 50 (
Wl) corner, height 60. The various sintering raw materials mentioned above were filled into a graphite mold of 1,800 mm in diameter, and then pushed into a high-frequency coil.
200k at each specified temperature within the temperature range from ℃ to 2050℃
A pressure of g/d was applied and held for 60 minutes, then the pressure was released and the mixture was allowed to cool to obtain a desired sintered body of 50×50×5.5 (m). Each sintered body was cut and ground with a diamond grindstone to create ten 3X4X36 (■゛) test pieces, and the measured values obtained by various tests were also used in the first test.
Shown in the table.

1 in Table 1 (hot press temperature 1800℃) 4 in Table 1
(Hot press temperature: 2000° C.) In Table 1 above, for example, 6 (ZrQL+6 mol% M90) refers to 6 (94 mol% ZrO+6 mol% M90) (the same applies hereinafter).

Experiment ■〉 The results of the sintered body were obtained when the raw material for sintering made in the same manner as in Experiment ■ was sintered under the heat isostatic pressure sintering (hereinafter referred to as HIP) conditions as shown in Table 2. The characteristics are shown in Table 2.

From the results in Table 2 and above, it can be seen that by adding erbium oxide and partially stabilized zirconium oxide to silicon carbide, the resulting sintered body becomes dense and finely grained, but the mechanism +r is not necessarily clear. It has not been precisely elucidated. However, the general idea is as follows (i.e., erbium oxide enters the crystal lattice of silicon carbide in a high temperature range, sintering progresses in the process, and the erbium oxide suppresses crystal grain growth. Partially stabilized zirconium oxide exists in a uniformly dispersed state without forming a solid solution in silicon carbide, and during sintering and cooling, a small amount of tetragonal crystals contained in it undergo phase transformation to monoclinic crystal, and The accompanying volumetric expansion applies stress to the surrounding silicon carbide matrix, making it exhibit high density and strength.Therefore, if the zirconium oxide used is in a stabilized state, there will be no volumetric expansion, so the density and strength will decrease. No increase is observed, and if unstabilized zirconium oxide is used, there are too many tetragonal crystals that expand in volume, so excessive stress is applied to the sintered body and cracks occur.

Considering the sintering conditions for hot sintering methods (hot press method and HIP method) based on the above experimental results, we found that a temperature of 1850°C or higher is required to obtain a dense and strong sintered body. However, if the temperature is too high, on the other hand, grain growth becomes intense and excessive grain growth occurs before sufficient densification occurs, leaving pores, so the upper limit should be 2000°C. As for the pressure, it is sufficient if it is 100 kg/d or more, and there is no particular limitation on the upper limit. Next, in the case of the hot press method, it is desirable that the sintering atmosphere be performed in a vacuum or in an inert gas, and in the case of the HIP method, it is desirable to perform the sintering in an inert gas.

Sintering temperature 1850-2000 in Tables 1 to 2 above
℃ and sintering pressure of 100 kg/cIIr or more, the data are summarized as shown in Table 3.

Unless the amount of erbium chloride is used is at least 5% by weight, the theoretical density will be low (and the transverse rupture strength and other properties will not be good either, but if it is too large (18% by weight), it will cause grain formation problems. The amount of partially stabilized zirconium oxide should be 5 to 15% by weight since this may cause harmful effects.Also, unless at least 2% by weight of partially stabilized zirconium oxide is used, the above-mentioned effect of addition cannot be achieved, and both the transverse rupture strength and Charpy impact value will decrease. Low, on the other hand, too high (
If the amount is as much as 8% by weight, various problems associated with grain growth will occur, so the amount is set at 2 to 6% by weight. It should be noted that 1-4 mol%, 2-6 mol% and 2-7 mol% of idria, magnesia and calcia, which are additives for partially stabilizing zirconium oxide, are experimentally preferred.

Part of the silicon carbide used next is Be, BeO+8J,
C+AI, AIN, A1.0. We will show an experiment for the case where .

Experiment I〉 SiC with purity 98.5%, average particle size 0, 5) t, m
Powder and purity 99.9%, average particle size 5Pm Er-process 04
The powder and various additives as listed in Table 3 were sintered at 1950° C. in the same manner as described in Experiment I, and various properties were investigated and the measured values are shown in Table 4.

Table 4 From Table 4, it is clear that even when silicon carbide is partially replaced with the various additives mentioned above, by adding appropriate amounts of erbium oxide and partially stabilized zirconium oxide, dense and fine granular sintered particles can be produced. It has been confirmed that it is possible to form a solid body, but
In this case, if the amount of substitution is about 0.5% by weight, there is not much difference compared to the unsubstituted product, but if it is too large and reaches 3.0% by weight, a decrease in transverse rupture strength and hardness will be seen. The amount of substitution is 2% by weight or less, preferably 0.5-2% by weight.

As described above, according to the present invention, a silicon carbide sintered body that is extremely dense, has fine crystal grains, and is rich in toughness can be obtained, and the sintered body has excellent practical properties. ,
Moreover, since it is manufactured using the hot press method or HIP method, it is easy to manufacture large sintered bodies, so it has excellent oxidation resistance.
It can be widely used as various structural members and wear-resistant members that require thermal shock resistance, corrosion resistance, high-temperature strength, etc.

Patent applicant Noriharu Ariyoshi, agent of Nippon Tungsten Co., Ltd.

Claims (1)

[Claims] 1. (a) 5 to 15% by weight of erbium oxide, (b) 1 to 4 mol% of itria, and 12 to 6 mol% of magnezium. A silicon carbide sintered body having a composition of 2 to 6% by weight of partially stabilized zirconium oxide in which at least 2 to 7 mol% of calcia is solid-dissolved and the balance is (c) silicon carbide. 2. The silicon carbide sintered body according to claim 1, which has a density of 96% or more of the theoretical density. 3. The silicon carbide sintered body according to claim 1, wherein the average particle size of the sintered body is 10 ibm or less. 4. Axis) Erbium oxide 5-15% by weight, (b) Ittria 1-4 mol%, Magnesium 12-6 mol%. 2 to 6% by weight of partially stabilized zirconium oxide in which one or more of 2 to 7 mol% of calcia is solid-dissolved, and the balance is (C) 2% by weight or less (not including 0) of Be, Be
A silicon carbide sintered body having a composition of silicon carbide substituted with one or more of 0r B, B, C+^I, A11ll, and ^1nyl. 5. The silicon carbide sintered body according to claim 4, which has a density of 96% or more of the theoretical density. 6. The silicon carbide sintered body according to claim 4, wherein the grain size of the sintered body is equal to or less than average IIS. 7. (a) 5 to 15% by weight of erbium oxide powder,
(b) 2 to 6% by weight of partially stabilized zirconium oxide powder in which one or more of 1 to 4 mol% of ittria, 2 to 6 mol% of magnesia, and 2 to 7 mol% of calcia are dissolved, and the balance is (c ) A method for producing a silicon carbide sintered body, comprising the steps of (b) mixing the mixture with silicon carbide powder, molding the mixture, and then sintering it by a hot sintering method. 8. The method for producing a silicon carbide sintered body according to claim 7, wherein the hot sintering method is a hot press method. 9. Hot press sintering conditions: temperature 1850-2000
9C and a pressure of 100 kg/cd or more. 10. 8. The method for producing a silicon carbide sintered body according to claim 7, wherein the hot sintering method is a hot isostatic pressing method. 11. Hot isostatic pressure sintering conditions were set at a temperature of 1850 to 20
11. The method for producing a silicon carbide sintered body according to claim 10, characterized in that the temperature is 00°C and the pressure is 100 kg/cd or more. 12. (a) Erbium oxide powder of 5 to 15% by weight b) A part in which one or more of 1 to 4 mol% of ittria, 2 to 6 mol% of magnesia, and 2 to 7 mol% of calcia is dissolved as a solid solution. 2 to 6% by weight of stabilized zirconium oxide powder and the balance (c) 2% by weight or less (not including 0) of Be
, Bed, B, B, C1Alp^1. A method for producing a silicon carbide sintered body, which comprises mixing and molding silicon carbide powder substituted with one or more types of Q7 powder, and then sintering by a hot sintering method. 13. The method for producing a silicon carbide sintered body according to claim 12, wherein the hot sintering method is a hot press method. 14. Hot press sintering conditions: temperature 1850~20
14. The method for producing a silicon carbide sintered body according to claim 13, characterized in that the temperature is 00°C and the pressure is 100 kg/ci or more. 15. The method for producing a silicon carbide sintered body according to claim 12, characterized in that the hot sintering method is a hot isostatic pressing method. 16. Hot isostatic pressure sintering conditions were set at a temperature of 1850 to 20
16. The method for producing a silicon carbide sintered body according to claim 15, characterized in that the temperature is 00°C and the pressure is 100 kg/cd or more.