JPS60231466A - High density silicon carbide sintered body - 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 [Industrial Application Field] The present invention relates to a silicon carbide sintered body having high density as well as oxidation resistance, thermal shock resistance, corrosion resistance and high temperature strength.

[Prior art and its problems]

In recent years, silicon carbide sintered bodies have been exploited for their excellent oxidation resistance, thermal shock resistance, corrosion resistance, and high-temperature strength to be used in various structural materials, check valves and sealing materials for corrosive liquids, and heat exchangers for high-temperature furnaces. As the use of sintered materials has expanded to include equipment materials and even strong wear-resistant materials, there has been a demand for sintered bodies with virtually no pores and greater strength.

Methods for producing silicon carbide include (a) gas phase reaction method, (
(b) Reactive sintering method and (c) Hot sintering method. Method (a) can obtain homogeneous and dense silicon carbide, but it can usually only produce a thin film. In practice, it is a coating method for various materials. The method (b) is usually a method of mixing silicon carbide, silicon dioxide, or silicon carbide powder and firing it, and although it is possible to obtain objects with a large shape, it is difficult to obtain dense objects, and at present, 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 sintered body that is thick (and dense) in shape.

However, since silicon carbide is a compound with large covalent bonds, it is hard, tough, and stable even at high temperatures, so it has extremely poor sinterability when used alone, making it difficult to obtain a sintered body that can be put to practical use. Since it is difficult to do so, there are reports of mixing various sintering aids (R, 8 II Fegro et al.
al, Journal of CeramicSo
ciety, 1956, vol. 39, 386-389
P'), JP-A-49-7311, JP-A-4
9-99308, JP 50-78609, JP 51-65111, JP 52-671
Publication No. 6, JP-A-53-67711, and JP-A-Sho 5
No. 3-84013, etc., 81. Fe,B.

It has been reported that if B4C 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 do not affect the strength and have a large influence.

The surface scratches in (B) can be avoided by paying attention to processing, and the porosity in (B) can be avoided by using various sintering aids as described above to obtain a sintered body with very low porosity. However, it still contains a lot of pores on a microscopic level. Furthermore, 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, which is the reason why it is not possible to increase the strength above a certain limit. There is. Regarding these facts, please read about the silicon carbide sintered body using B as a sintering aid! '7 etc. (S, Prochazka et al.
,, awe.

aram, Soc, Bull, 52885-89
1 (1973)) reported that crystal grains grow and their strength does not become very large.

Therefore, in order to eliminate the above-mentioned drawbacks, the inventor of the present invention applied for a patent application in 1983.
In the application No. 190361, a silicon carbide sintered body with high density and fine crystal grains was disclosed, in which erbium oxide and aluminum oxide were present in the silicon carbide sintered body as individual compositions. However, this sintered body also has a bore of around 2 μm, and the crystal grains are also 8.5 mm.
Silicon carbide sintered bodies are found to be as large as μ mackerel, and a silicon carbide sintered body with higher density and finer crystal grains is required.

- [Problems to be Solved by the Invention] The purpose of the present invention is to create a highly dense carbide material with finer bores and structures than conventional silicon carbide sintered materials, with a grain size of less than 5 μm and a grain size of less than 5 μm. The present invention aims to provide a highly dense silicon carbide sintered material.

[Means for solving problems]

The silicon carbide sintered body of the present invention contains erbium oxide and aluminum oxide in the form of a composite oxide.

For example, as one of the composite oxides, it can exist in the form of garnet shown in the following formula.

Era(AI, Er)t(AIOa)+ --------
--(1) (Er, AI)s^It(AlO2)s -
-------------(2> As the garnet powder represented by the above formulas (1) and (2), for example, a mixed powder of aluminum oxide powder and erbium oxide powder is heated at a high temperature (usually 1300 to 1600 It is possible to use polycrystalline powder obtained by solid-phase reaction at a temperature of about 30°F (°C).

In such a solid-phase reaction, a product having the composition Er5AIz(AlO2)s is not necessarily produced;
Garnets with the composition shown are often obtained.

In addition, garnet having a composition of Er3A12(^104)3 can also be used. In addition to Garnet, Er
A composition represented by x Al +1-Xl 03 (here x<1) can also be used.

The amount of erbium oxide in the composite oxide is at least 2
If it is less than 15% by weight, the theoretical density will be low and the transverse rupture strength and other mechanical properties will not be good, but if the amount is as high as 15% by weight, the growth of crystal grains will be observed, and the transverse rupture strength and impact value will decrease accordingly. However, most of the other properties also tend to deteriorate. Therefore, the amount should be within 12% by weight.

On the other hand, when the amount of aluminum oxide reaches 3% by weight, a decrease in properties such as transverse rupture strength is observed, and if no addition is made, the effect of adding garnet to erbium oxide and aluminum oxide is not at all, so it is preferable to % by weight or less.

Although the mechanism of the densification of the structure of this composite oxide has not yet been precisely elucidated, the sintering of silicon carbide is promoted by solid solution in silicon carbide due to low activation energy during sintering. This is thought to be due to the

Furthermore, the present invention uses at least one element selected from the following component group as a sintering accelerator for high densification or a compound such as its oxide, nitride, boride, or carbide in an amount of 0.5 to 6 Add .0% by weight. Examples of elements having this function include titanium, vanadium, chromium, manganese, magnesium, yttrium, zirconium, niobium, molybdenum, barium, lanthanum, cerium, gadolinium, hafnium, tantalum, tungsten, thorium, and cesium.

Furthermore, the amount of the second additive element that promotes sintering is almost ineffective at 0.3 wt.%, and a minimum of 0.5 wt.% is required; if the amount is too large and exceeds 6 wt.%, crystal grain growth will occur. Visibility characteristics deteriorate. Although the mechanism by which these elements affect the sintered body is not yet clear, it has been confirmed through experiments that the synergistic effect with the composite oxide results in very few microscopic pores.

In addition, a part of silicon carbide is Be, Bed, B, B
It can also be replaced with 4C. In this case, by adding an appropriate amount of a composite oxide of erbium oxide and aluminum oxide, a sintered body having a dense and fine-grained structure can be obtained. In this case, the amount of substitution is up to about 0.5% by weight.
There is not much difference compared to the unsubstituted product, but when it reaches 3.0% by weight, the transverse rupture strength and hardness decrease, so the amount of substitution is 2% by weight or less, preferably 0.5 to 2% by weight. There is a need to.

Furthermore, it has been confirmed through experiments that even if silicon carbide contains 0.5 to 2% by weight of free carbon, the results are not affected.

In producing the sintered body of the present invention, it is necessary that the composite oxide, sintering accelerator, etc. be uniformly dispersed in silicon carbide.

Further, in manufacturing the sintered body of the present invention, hot sintering methods such as the hot press method and the old P method can be suitably used.

In order to obtain a dense and strong sintered body, a hot press temperature of 1900°C or higher is required; however, if the temperature reaches 2100°C, grain growth will become intense, resulting in excessive grain formation before sufficient densification. Growth occurs and pores remain. Regarding the pressure, a pressure of 100 kg/cm or more is sufficient, and the upper limit is not particularly limited.The sintering atmosphere should be in a vacuum or an inert gas; It is preferable to do this in an active gas.

Also, almost the same sintered body can be obtained using the ordinary sintering method, and the temperature at this time is 205°C in an unpressurized inert gas.
It can be obtained in a temperature range of 2000°C to 2250°C in a pressurized gas of 0°C to 2300°C and 10 atm or less.

〔Example〕

Example 1 First, aluminum oxide powder with a purity of 99.9% and an average particle size of 0.4 μm and an aluminum oxide powder with a purity of 99.9% and an average particle size of 0.8
[mu]m erbium oxide powder was mixed with the composition shown in Table 1, and the mixed powder was heated at 1300 to 1600[deg.] C. for 3 to IO hours to synthesize garnet.

The obtained garnet was finely ground to an average size of 0.5 μm, and
Silicon carbide powder with a purity of 98.5% and an average particle size of 0.5 μm and magnesia oxide powder with a purity of 99.9% and an average particle size of 1 μm were added and blended to obtain the composition shown in the table.

The same compound was mixed and pulverized for 15 hours using a ball mill mixer, and then thoroughly dried to be used as a raw material for sintering.
A graphite mold measuring 50×50+n square and 60 m in height was filled with the various sintering materials described above and inserted into a high-frequency coil. 19
A pressure of 200 kg/cm" was applied at 50°C, held for 60 minutes, and then the pressure was released and allowed to cool.
A desired sintered body of 50 x 5.5 m was obtained.

Cut and grind each sintered body with a diamond grindstone to obtain 10 pieces each.
A number of 3 x 4 x 35 dragon test pieces were prepared and subjected to various tests. The obtained measured values are shown in Table 1.

In addition, by observing the structure of each test piece, the pore size was 2 μm.
Large objects are marked with an X, and fine objects of 1 μm or less are marked with an ○.
Indicated by a mark.

Table 1-1 (Table 1-2 ω roasting example) Example 2 The sample obtained in Example 1 was cut into a 10X10X5U+ plate with a diamond grindstone, and the surface was ground with a @200 diamond grindstone. 1 (The lfi surface was blasted with an air pressure of 5 kg/e using a sandblasting machine with a nozzle with an inner diameter of 8 fi.
Abrasive grains (Methycolite C, No. 40) were sprayed at a spraying distance of 50+n+ using a 100mm-sized sample, and the weight loss was measured. The results are shown in Table 2.

Table 2 Example 3 The sample obtained in Example 1 was cut into a 1010 x 10 x 5 plate with a diamond grinding wheel, and the entire surface was ground with a '200 diamond grinding wheel, and the specimen was placed in the atmosphere at 1300°C for 20
The sample was left to stand for a period of time, and the amount of weight increase per unit area at that time was measured. The results are shown in Table 3.

Table 3 Example 4 The entire surface of the sample obtained in Example 1 was ground to a size of 3 x 4 x 35 mm with a diamond grindstone, and the specimen was placed in the atmosphere.
Charpy impact value at 50°C was measured. The results are shown in Table 4.

Table 4 Example 5 A high temperature fatigue test was conducted using the sample obtained in Example 1 as a specimen. The method used was partial repetition, using a bending tester, in the atmosphere at 1000°C, with a distance between supports of 20m, and 1
Repeated stress was applied at a rate of 325 times/min. The method of applying the repeated stress is as shown in the drawing, where the upper limit stress is σ11aX+, the lower limit stress is σljn, the average stress is σm, the stress amplitude is σa, and when i−σa/σM, σmax −15kir/cd+ The test was carried out under the condition that i=0.73. The results are shown in Table 5.

Table 5 Example 6 First, 10% by weight of aluminum oxide powder with a purity of 99.9% and an average particle size of 0.4 μm, and 90% by weight of erbium oxide powder with a purity of 99.9% and an average particle size of 0.8 μm. % and heated this mixed powder at 1400° C. for 5 hours to synthesize garnet. The obtained garnet was then finely ground to an average size of 0.5 μm. 10% by weight of the powder and a second additional element that promotes sintering were added in the proportions shown in Table 6, and the remainder was 98.5% by weight, with an average particle size of 0.
．． Various types of silicon carbide powder were mixed to obtain 5 μm silicon carbide powder, and heated and pulverized for 15 hours using a ball mill mixer. A sintered body was prepared in the same manner as in Example 1, and the results of the investigation were also shown in Example 6. Shown in the table.

Table 6 Example 7 A portion of the silicon carbide powder used next is Be and Bed.

Example 1 showing the case of substitution with B, B, and C 1 First, aluminum oxide powder with a purity of 99.9% and an average particle size of 0.4 μm, and an aluminum oxide powder with a purity of 99.9% and an average particle size of 0.1 μm.
and erbium oxide powder in the composition shown in Table 7, and this mixed powder was heated at 1300 to 1600°C for 13 to 10 hours to synthesize garnet. Next, the obtained garnet was finely ground to an average particle size of 0.5 μm, and the purity was 98.5% and the average particle size was 0.5 μm so that the composition shown in Table 7 was obtained.
silicon carbide powder and purity 99.9%.

Magnesia oxide powder with an average particle size of 1 μm was added and blended, mixed and pulverized for 15 hours using a ball mill mixer, and then hot press baked at a temperature of 1950°C in the same manner as described in Example 1. Table 7 shows the measured values obtained by investigating various characteristics.

Table 7 In the present invention, as shown in the above examples, the density of the sintered body is increased by adding a composite oxide of aluminum oxide and erbium oxide and various elements that promote sintering, and the crystalline structure is increased. The pore size is considered fine as 5 μm or less, and the pore size is 1 μm.
A very fine and tough sintered body can be obtained.

On the other hand, when a mixed powder of aluminum oxide and erbium oxide as shown in the comparative example in Table 1-2 is used, the pore size is as large as about 2 μm.

(Effects of the Invention) The sintered body of the present invention is extremely dense, has a very fine bore size of 1.0 μm or less, and has a fine structure with a crystal grain size of 5 μm or less. It also has excellent mechanical properties.

Therefore, it can be widely used as various structural members and wear members that require oxidation resistance, thermal shock resistance, corrosion resistance, high-temperature strength, etc.

Moreover, since the sintered body of the present invention can be manufactured by the Ho/Dobres method or the old P method, it is easy to manufacture a large sintered body. Sintering using the normal sintering method also has the effect of producing a sintered body almost equivalent to hot pressure sintering.

[Brief explanation of drawings]

The attached drawing is an explanatory diagram of the high temperature fatigue test in Example 6.

Claims (1)

[Claims] 1. Consisting of erbium oxide = 2 to 12% by weight, aluminum oxide: 2% by weight or less, and the balance: silicon carbide,
A high-density silicon carbide sintered body characterized in that the erbium oxide and aluminum oxide are all present as a composite oxide. 2. Part of the silicon carbide powder is Be+ BeO, B,
High-density silicon carbide sintered body-03 according to claim 1, which is substituted by 84C, erbium Mide: 2 to 12% by weight, aluminum oxide = 2% by weight or less, At least one element or compound thereof selected from the following A component group: 0.5 to 6.0% by weight, and the remainder: silicon carbide, and the erbium oxide and aluminum oxide are all present as a composite oxide A high-density silicon carbide sintered body characterized by: A component: titanium, vanadium, chromium. Manganese, magnesium 7 yttrium, zirconium, niobium, molybdenum, barium, lanthanum, cerium, gadolinium, hafnium, tankard, tungsten, thorium and cesium. 4. Part of silicon carbide powder is Be + Be O+
The high-density silicon carbide sintered body according to claim 3, characterized in that B*B t C is substituted.