JPS6126566A - Method of sintering sic composite 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 Field of Industrial Application The present invention relates to a method for producing a SiC composite; 1. In particular, the present invention relates to a manufacturing method that allows a dense and high-strength SiC composite to be obtained even with so-called normal sintering, in which sintering is performed without pressure after molding.

Conventional technology SiC has high hardness, excellent wear resistance, low coefficient of thermal expansion, high decomposition temperature, high oxidation resistance, chemical stability, and generally has considerable electrical conductivity. Known as a useful ceramic material. This S
In addition to the above-mentioned properties, iC's high-density sintered body has high strength up to high temperatures and excellent heat shock resistance, making it promising as a high-temperature structural material, and its application has been attempted in a variety of applications including gas turbines. ing. Since SiC is a compound with strong covalent bonding properties, it is difficult to sinter it alone, and in order to obtain a high-density sintered body, it is necessary to add some kind of sintering aid. In the case of the hot press method, B, 84C, Ac or AIN are known as sintering aids. In addition, in the case of pressureless sintering method, B, B4C, At, At
It is known to add carbon in addition to N.

Problems to be Solved by the Invention However, in the method using the pressureless sintering aid, the amount of the aid added is within a limited range, and the amount of the aid compound is also limited. The physical properties of are also limited.

Further, in the case of the hot press method, since sintering is progressed while applying negative axis pressure, only products with simple shapes can be obtained, and it is not suitable for manufacturing products with complex shapes. On the other hand, in the case of the pressureless sintering method, SiC
There is a drawback that hydrogen cannot be used easily for mixing with the additives, and the dispersion of additives is generally poor. In addition, in the degreasing process after molding, there are many active auxiliary agents such as 'C', making it difficult to use an air atmosphere.

Means for Solving the Problems The present invention was developed as a result of repeated experiments with the aim of sintering a SiC composite with properties equal to or better than conventional ones even by a normal sintering method without using the hot press method. The invention has led to the present invention, and the present invention uses a substance containing Am element as a sintering aid in an amount of 0.01-20% in terms of metal N weight, and Be5B and AI as additives.

After molding a mixture in which 0.1% or more of L containing at least one of group IVa elements, group a elements, or group a elements is blended, and the remainder is substantially SiC. The gist of this method is to obtain a SiC composite by sintering in a non-oxidizing atmosphere.

The raw materials, manufacturing method, etc. of the present invention will be specifically explained below.

First, as the SiC raw material, either the α-form or the β-form can be used. A purity of 98% or more is preferred, but purity of 90 to 98% can also be used effectively. In the case of extremely fine particles, it is more appropriate to express the particle size by the specific surface area rather than the average particle diameter.In order to advantageously achieve the object of the present invention, the specific surface area should be 5 m27g or more, preferably 10+L12/g.
It is better to use more than one.

Next, the A9 element-containing substance as a sintering aid and the various element-containing substances as additives may be metals or compounds with other elements, but they can be crushed, mixed, molded, Those that are stable during processes such as degreasing are preferred, and oxides, carbides, nitrides, silicides, borides, or complex compounds thereof are preferred. The compound does not need to be in that form at the time of blending, and may be converted during an intermediate step such as degreasing or heating during sintering. The sintering aids and various alcoholates and hydroxides of additive elements are suitable examples.For example, they form oxides in air, form nitrides in nitrogen atmosphere, and form carbon oxides. If they are in a shared state, conversion such as the formation of carbides will occur. Since the shape of the added 7c element must be well-dispersed in the molded body, it is preferable to use one having a specific surface area of 5+n2/Fi or less if it is liquid or solid.

The amount of A9 contained in the sintering aid is 0.01 to 2 in terms of metal weight.
It is 0%. If it is less than 0.01%, mi conversion is not sufficient,
Moreover, if it exceeds 20%, the sintered body tends to become porous, and SiC
This is undesirable because it deteriorates the property of high temperature strength, which is a characteristic of the powder.

The lower limit of the amount of additives added is 0.1% by metal weight of the added element.
%. Below this range, even if sintered, densification often does not proceed sufficiently, and there is no effect of improving the properties of the composite. The upper limit of the amount added depends on the density of the sintered body as well as the additive and Si.
Although there are no practical limitations, this is determined by experimentally determining the preferred properties of the complex of C.
For the purpose of prioritizing the physical properties of SiC, approximately 50
It is common sense to set it as %.

Next, as the molding method in the present invention, all methods commonly used for molding ceramics can be used. That is, press molding, slurry casting, injection molding, extrusion molding, etc. are suitable. Firing in a non-oxidizing atmosphere at 1900~2
It is necessary to carry out at 300°C. As the non-oxidizing atmosphere, nitrogen, argon, helium, hydrogen, etc. can be used, and among them, argon and helium are convenient and preferred. The temperature is more preferably 1950-2200°C. If the blackness is lower than 1900°C, densification will not proceed sufficiently and a high-density sintered body will not be obtained. Usually 0.1 to 24 hours are required, more preferably 0.5 to 24 hours.
1 () hours. This is because if the time is too short, the material will not be densified, and even if it is densified, sufficient strength will not be produced, and if the time is too short, it will decompose too much and become porous, which is often undesirable. The atmospheric pressure may be no pressure or reduced pressure, or a hot isostatic press method may be used. Of course, a hot press method is also possible.

Function The sintering process of the present invention will now be explained as follows. It is believed that Al element plays an essential role as an auxiliary agent in the sintering of SiC itself. The A9 element-containing material generates AI vapor at the sintering temperature or directly reacts with SiC or its surface oxide to form a liquid phase, and favorable grain growth of SiC particles occurs in the presence of the liquid phase. It is thought that evaporation of the liquid phase with an angle of τ occurs and that detachment from the molded body also progresses. The formation of this liquid phase may be influenced by Si and SiO vapor generated from SiC and the carbon atmosphere from graphite normally used in sintering containers, but the detailed mechanism is not clear. It is possible to produce a SiC composite as long as the additive does not inhibit or promote the formation of this preferred liquid phase, and also does not inhibit or promote the wettability of this liquid phase to the SiC surface, and furthermore, the SiC sinterability. The additive of the present invention is an example. However, if no sintering aid is included and only the additive is added, sintering hardly occurs, so that the role of the additive in the present invention can be better understood. Note that in the case of a compound that does not contribute or makes a small contribution to the formation of a liquid phase at the internal sintering temperature of the Al-containing material, it can be considered as an additive.

In the case of elemental additives other than those of the present invention, the effect of the additives of the present invention is obvious because the molded product either does not become densified, or even if it becomes densified, it foams and becomes porous.

Effects of the Invention As described above, the present invention allows the type, form, and amount of elements to be selected from a much wider range than conventional sintering additive elements in pressureless sintering, and thereby improves the physical properties of the SiC composite, such as electrical conductivity, It has the advantage that the coefficient of thermal expansion, thermal conductivity, etc. can be selected from a wide range. Furthermore, since carbon is not used as an additive element for sintering, water can be used for mixing with SiC, which allows the additive to be sufficiently dispersed.
Furthermore, in the degreasing process, additives that do not contain carbon and can be degreased in air can be selected. Furthermore, in sintering, a so-called hot isostatic press method in which the pressure of non-oxidizing gas is increased can also be applied.

The composite sintered body made of SiC and additives obtained in the present invention can be provided with various properties in addition to the properties of SiC. For example, S
The electrical resistance of the iC sintered body is usually about 10° to 104 Ω・cm, but by adding 7% + group a, ■a group, and ■a group elements, the electrical resistance is reduced to 10−′Ω・0m or less. This gives the SiC sintered body, which is difficult to machine, the advantage of facilitating electrical discharge machining. Also, BeO,
By adding BN, %N, 1203, etc., it is possible to produce a sintered body with an electrical resistance of 105 or more, which can be applied to electronic circuits and the like. It is clear that the wider the range of values for other physical properties, the wider the range of application.

Although the advantages of the present invention are clear as described above, the following advantages can also be mentioned. In other words, since the additive elements that can be applied in the present invention are wide-ranging, the additive elements of the present invention include impurities that are unavoidably mixed in during the production of raw material SiC or the pulverization process, and elements that are intentionally added. If selected, sintering can be performed without going through the process of blending additives, and this is also within the scope of the present invention. In addition, elements other than the elements added in the present invention will not have a particularly bad effect on sintering if they are in small amounts, and the fact that oxides, nitrides, silicides, etc. can be used as additives means that the raw material Si
This shows that sufficient sintering is possible even if C is slightly oxidized or nitrided or contains free silicon.

Examples As described above, the present invention is industrially extremely advantageous.
This will be further understood by the examples given below. In Examples 1 to 18 shown in Table 1, SiC powder and sintering aids and additives with a purity of 98% or more were mixed and dried as a powder of 3 m27 g or more in the case of liquid or solid.
Hydroformed with 15001c, 8/cI02, 10X5
A molded body of X60+II+n was obtained by storing this molded body in a carbon crucible with a lid, placing the carbon crucible in an argon gas atmosphere, and sintering it under the firing conditions shown in Table tIc1. The density of each sintered body,
The bending strength and electrical resistance are shown in Table 1.

Claims (4)

[Claims] (1) 0.01 to 20% of Al element-containing material as a sintering aid in terms of metal Al weight, and Be, B, and A as additives.
After forming a mixture containing at least one of group IVa elements, group Va elements, or group VIa elements in an amount of 0.1% or more in terms of weight, the remainder being essentially SiC, the mixture is non-oxidized. 1. A method for sintering a SiC composite, the method comprising sintering in a neutral atmosphere. (2) The sintering method according to claim 1, wherein the sintering is performed without pressure or with pressurization of non-oxidizing gas. (3) The sintering aid or additive is converted into an oxide, carbide, nitride, silicide, boride, or a composite thereof during blending or during the process leading to sintering. A sintering method according to claim 1 or 2. (4) The sintering method according to claim 1 or 2, wherein the sintering temperature is 1900 to 2300°C.