JPH02204375A - Fiber reinforced ceramics - Google Patents

Abstract

PURPOSE:To provide the above ceramics which is excellent in heat resistance, oxidation resistance, strength, toughness, etc., by compounding prescribed ratios of SiC contg. SiC whiskers and specific two kinds of sintering assistants with silicon oxynitride (forming component) and calcining the mixture. CONSTITUTION:(A) 5 to 50wt.% SiC contg. the SiC whiskers at >=5wt.% of the total essential component, (B) 0.1 to 25wt.% 1st sintering assistant consisting of >=1 kinds selected from the oxides of Al, Sc, Y and rare earth elements (e.g.; Y2O3), (C) 0.05 to 5wt.% 2nd sintering assistant consisting of >=1 kinds selected from the oxides of the metal elements belonging to groups VA and VIA of periodic table (e.g.; Cr2O3), and (D) the balance silicon oxynitride or silicon oxynitride forming component consisting of silicon nitride and silicon oxide or mixture composed of both are mixed. The resulted starting raw material is calcined and the fiber-reinforced ceramics adequate for cutting tools, sliding members, engine members, etc., is thereby produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to fiber-reinforced ceramics mainly composed of silicon oxynitride (Si2N2O) reinforced with SiC whiskers.

[Prior art] In recent years, high strength, high toughness, wear resistance, chipping resistance, and acid resistance are being used in cutting tools, sliding members, automobile engine parts such as ceramic valves, and heat engine parts such as gas turbine rotors. There is a need for ceramic materials with excellent chemical resistance and heat resistance.

As one of the ceramic materials with excellent oxidation resistance and heat resistance, JP-A-63-176369 and JP-A-63-129
No. 067, JP-A-62-223066, JP-A-59-
Silicon oxynitrides described in Japanese Patent Laid-Open No. 169981 and Japanese Patent Application Laid-open No. 123110/1988 are known.

[Problems to be Solved by the Invention] However, although the conventional silicon oxynitride sintered body has excellent heat resistance and oxidation resistance, it is difficult to use it for various structural members due to its mechanical strength, toughness, and hardness. characteristics are insufficient. For example, regarding strength, there is a method of sintering in nail powder made of a mixture of silicon nitride and silicon oxide as in JP-A-63-176369, and
Although there is a sintered body made of i3Na-5iO2SiC, its bending strength is about 40 to 60 kg/mm'', which is still not sufficient for use in the above-mentioned applications.

As a method to deal with these issues, it is already known that the toughness of alumina (AQ203), mullite <3AQ203・2SiCh), etc. can be improved by i-addition of SIC whiskers. Addition does not necessarily increase the toughness of ceramics. For example, as seen in the following document, even if SiC whiskers are added to 5L3N4, which has a similar composition to that of the present invention, the toughness may only be improved to a certain degree, or may even be reduced.

<Literature> Collection of lecture abstracts of the 25th Ceramics Industry Basics Conference.

2A15 (1987) Collection of abstracts from the 7th High Temperature Materials Basics Conference.

25-29 (1987) Arn, CCra, m, Sac, Bul 1°66 (
2), 330-333 In view of the above circumstances, the inventors of the present application have conducted various experiments and have developed a fiber whose toughness has been improved to some extent by modifying the amount of SiC whiskers added and the sintering aid. We provide reinforced ceramics (Patent application 127687/1987)
No.) 6 The present invention was made in view of the above circumstances, and by improving the sintering aid of the previous invention, it improves not only the strength, toughness and hardness of the layer, but also the heat resistance and oxidation resistance. The purpose of the present invention is to provide m-fiber-reinforced ceramics with excellent mechanical properties.

[Means for Solving the Problems] The present invention employs the following means to solve the above problems.

That is, the first gist of the invention of the present application is: a first sintered material comprising: SiC containing SiC whiskers; and one or more oxides selected from oxides of 80, Sc, Y, and rare earth elements. an auxiliary agent, a second sintering agent consisting of one or more oxides of metal elements belonging to groups VA and IA of the periodic table, and the remainder, silicon oxynitride or silicon nitride. A fiber-reinforced ceramic in which a starting material is formed with a silicon oxynitride-forming component consisting of silicon oxide or a mixture of the two and fired, the composition of each of the above components being 5 to 50% by weight of SiC,
Among them, SiC whiskers are prepared to account for at least 5% by weight or more of the total main components, and the first sintering aid is adjusted to 0.0% by weight.
It is characterized in that the amount of the second sintering aid is 0.05 to 5% by weight.

Here, commercially available SiC whiskers can be used, and their typical shape is an average diameter of 0.2 to 5 um and an average length of 2 to 200 um. In particular, AQ, Ca, Mg, Ni, Fe, Co,
It is preferable that the crystal be a whisker-like crystal with less cationic impurities such as Mn and Cr, and less constrictions, branching, and single-plane defects. Furthermore, the surface of this SiC whisker may be coated with BN, carbon, or the like.

In the present invention, if the SiC whiskers are less than 5% by weight of the total main components, sufficient strength and toughness are not exhibited. Also, Si
If the content of SiC containing C whiskers is less than 5% by weight, it is not possible to suppress the decomposition of silicon oxynitride during sintering, and
There is no improvement in strength or toughness due to SiC whiskers. on the other hand,
If SiC exceeds 50% by weight, sinterability deteriorates.1. The desired fiber-reinforced ceramics cannot be obtained. S
It is preferable that the iC is composed only of SiC whiskers, and the amount thereof added is 10 to 45% by weight of the total component, since the strength and toughness are particularly high, and the sinterability is also sufficient.

A first sintering aid and a second sintering aid are added to this ceramic.

First, the first sintering aid is made of one or more selected oxides of AQ, Sc, Y, and rare earth elements, and is particularly preferably 5C203, Y20a, La
20a, Ce 02. Nd203. D
y20i.

It may be selected from the compound group of HO203, Yb20:+. If the amount added is less than 0.1% by weight, sinterability will deteriorate and the desired fiber-reinforced ceramics cannot be obtained. It is necessary that the content is 1% by weight or more, and it is particularly preferable that the amount added is 0.5 to 10% by weight because it has high strength and excellent heat resistance and oxidation resistance.

Note that when A Q 203 is selected as the oxide, part or all of As2O3 is dissolved in silicon oxynitride of the obtained sintered body to form S l 2-XA Q X O+. X
There is no problem even if N2-X (O”-siacon, X≦0.2).

The second sintering aid is selected from oxides of metal elements belonging to Groups VA and VIA of the periodic table, and is particularly preferably selected from the group of compounds V2O5, Tapo5°Cr2ch. good. The amount added is 0.05
If it is less than % by weight, there is almost no contribution; on the other hand,
If it is more than 5% by weight, for example, it will react with carbon type,
Because it forms various compounds and causes a decrease in strength,
0.05 to 5% by weight is suitable, especially 0.1 to 2.0% by weight.
It is preferable that the amount is % by weight because the sinterability is good.

As described below, silicon oxynitride is a compound that easily decomposes, so these oxides, which are the second sintering aids,
- Added to promote layer densification and reduce residual 5L3N4, etc.

Note that if the total amount of the first sintering aid and the second sintering aid exceeds 30% by weight, the glass component in the fiber-reinforced ceramic will become too large and the strength will deteriorate.

Since a decrease in heat resistance and oxidation resistance is observed, the content needs to be 30% by weight or less.

The remainder consists of a silicon oxynitride component. As the silicon oxynitride component, a silicon oxynitride powder, a mixed powder of silicon nitride and silicon dioxide, or a mixed powder of both can be used. The mixing ratio of silicon nitride and silicon dioxide is not particularly limited, but in order to obtain fiber-reinforced ceramics with high characteristics, the molar ratio is 5i3Nn:5jo2=1: 1.2 to 1.2:
It is desirable to have a degree of 1 degree.

Note that the oxide and 5i02 used in the present invention do not need to be in powder form from the beginning, but can be prepared by mixing the metal alkoxide (metal alkoxide) and colloidal silica (silica silica) forms, and then hydrolyzing and calcining them. It is also possible to use it as the raw material base of the present invention.

In addition to the above main components, β-513Na, Re2s 1207 (Re: rare earth element), etc. may be included to an extent that does not affect the properties, but in order to obtain fiber-reinforced ceramics with higher properties, it is necessary to Body X-ray circuit IJT Te, S
12N20. Other than S i C (7) Compound c7)
It is desirable that the integrated intensity of the strongest peak is 1/2 or less of the integrated intensity of the strongest peak ((200) or (l l I)) of S 12NpO.

Next, to outline the manufacturing method of fiber-reinforced ceramics having the above composition, first, the various components mentioned above are selected and mixed, and then, for example, the well-known hot press (HP) method, gas pressure sintering (GPS) method, hot A firing process is performed using an isostatic hydrostatic pressure (E-IIP) method or the like. In any sintering method, it is necessary to use a non-oxidizing atmosphere, and N2
In the case of the atmosphere, sintering is performed at 1600 to 2000° C. in a non-oxidizing atmosphere with a N2 partial pressure of 1 atm or more. Preferably, it is carried out in a N2 atmosphere of 1 atm or more. The most desirable sintering process is sintering by the HP method in a N2 atmosphere of 1 atm or higher. In this way, N of 1 atm or more
The reason why this is carried out in a 2 atmosphere is that silicon oxynitride is extremely easily decomposed as described later, and it is preferable for the N2 partial pressure to be 1 atm or more in order to suppress decomposition.

Therefore, in order to effectively suppress the decomposition of silicon oxynitride by N2, the N2 partial pressure should be adjusted as the firing temperature increases and
The smaller the amount of the various oxides mentioned above, the higher the amount needs to be.

Furthermore, it is preferable to set the sintering temperature as described above because it is not possible to obtain fiber-reinforced ceramics with sufficient wI density at temperatures below 1600°C;
This is because if the temperature exceeds 0° C., it becomes extremely difficult to suppress the decomposition of silicon oxynitride.

[Functions and Effects] The various additives and sintering conditions used in the present invention are thought to function as follows.

When silicon nitride and silicon dioxide are used as silicon oxynitride components, the chemical reaction formula between the two is shown as shown in (3).

S 1aNa+s i 02→2SjaN20...
・The reaction of ■■ hardly progresses in the solid phase. here,
80. The first sintering aid consisting of one or more oxides selected from Sc, Y, and rare earth elements generates a liquid phase together with silicon dioxide and promotes the reaction (2). It also promotes sintering of 5i2N20 produced. At this time, if 812N20 is added in advance as a seed crystal, the reaction (2) becomes even faster.

In addition, the second sintering aid selected from oxides of metal elements belonging to the VA and VIA groups is thought to work as an oxygen supply agent to Si3N4, promoting the reaction (2). do. This is because the valence of these metal elements is extremely variable. That is, by adding this second sintering aid, residual 543N4 and the like can be reduced, and the sintered body can be made more dense.

The reaction (2) rapidly proceeds at 1600°C or higher in the presence of these additives. Then, when the temperature exceeds 1700℃,
Rapidly decomposes according to reaction formula (2).

3Sj2N20→S i3N4+3S i O+N2
...■ When a carbon sheath or mold is used in the firing process, the decomposition of ■ can be suppressed by adding 5iCe. This is SiO produced by decomposition.
Because it is reactive, it reacts with surrounding carbon and tends to generate SiC on the outer periphery of the sintered body, which is an obstacle to densification.
It is thought that adding SiC in advance suppresses the reaction between SiO and C, thereby suppressing the decomposition of (2). This effect of suppressing the decomposition of SiC can be achieved by using SiC containing SiC whiskers.
In addition to forming a dense body through iC, under the constituent phase of the present invention, the strengthening effect of the material by the SiC whisker itself is effectively exhibited, providing high strength and toughness to the organ-reinforced ceramics. can be done.

It is clear from equation (2) that N2 at a pressure of 1 atm or higher in the firing process suppresses the decomposition of (2).

Therefore, the structure of the present invention provides high strength.

This made it possible to provide a ceramic material that is highly tough and has excellent wear resistance, chipping resistance, oxidation resistance, and heat resistance.

[Example] Examples of the present invention will be described.

The raw materials shown below were blended in the proportions shown in Table 1, uniformly dispersed and mixed in ethanol for 16 hours using a ball mill, dried, and granulated to obtain a base powder.

raw materials> (1) Silicon oxynitride component ■ 5i3Nz: Average particle size 0. 6ttm.

Purity 98%, alpha rate 90% ■ SiO2: average particle size 15 nm.

Purity 99.9% ■ 5i2N20: Average particle size 1 μm.

Purity 95% (2) First sintering aid AC! , Sc, Y and rare earth element oxides: average particle size 2
Less than μm (3) Second sintering aid Oxide of metal element in groups VA and VIA of the periodic table: Average particle size 2
Less than μm (4) SiC ■ SiC powder: average particle size 1. 6 μm.

Purity 96% ■ SiC whisker: average diameter 0.6 μm length 10-8
0um This base powder was sintered by hot pressing at the temperature and pressure shown in Table 1 for 1 hour in an atmosphere and N2 partial pressure to form a 4mm x 3
rr) The sample was processed into a size of 40 mm x 40 mm.

Thereafter, bending strength (flexural strength based on JIS-R1601), fracture toughness (indentation microfracture method, load 10 kg), and Vickers hardness (load 10 kg) were measured for the sample at room temperature and at 1000°C. In addition, the crystal phase in the sample was identified using X-ray diffraction, and the results are listed in Table 2 together with the above test results.

Furthermore, the results of sample observation using an electron microscope and X-ray diffraction revealed that SiC whiskers were dispersed in the sample in the form of whiskers without chemically reacting with other components.

It was confirmed that it remained.

The following was found from Tables 1 and 2.

■ As in sample No. 13.14, the first sintering aid,
Unless the second sintering aid and SiC containing SiC whiskers are included, densification will not occur.

■ Even if a sintering aid is added, if SiC whiskers are not used, the 5i2N20 component decomposes and volatilizes as shown in sample No. 15, so sintering may not be possible, or sample No. 1
Even if it is sintered at a low temperature like No. 6, only a product with low mechanical strength can be obtained.

■ S containing SiC whiskers, such as sample No. 17
When iC is less than 5% by weight, decomposition and volatilization of 5i2N20 cannot be suppressed.

■ Like sample No. 18, S containing SiC whiskers
When more than 40% by weight of iC is added, densification cannot be achieved unless the second sintering aid is added. That is, the addition of the second sintering aid improves the sinterability and allows densification even when SiC whiskers are added in an amount of 40% by weight or more.

■ Like sample No. 19, silicon oxynitride component and SiC
SiC containing whiskers alone cannot be densified.

(2) When the amount of the sintering aid added is less than 1% by weight, as in sample No. 20, m-density cannot be achieved using only the first sintering aid.

(2) When the sintering aid is added in an amount of 30% by weight or more, as in sample No. 21, the hot strength decreases.

(2) If SiC whiskers are not added in an amount of 5% by weight or more of the total weight, as in sample No. 22, sufficient toughness is not exhibited.

■Also, even if the second sintering aid is added, if the amount of the second sintering aid is too large as in sample No. 23, the mechanical strength will decrease and the sample When the total amount of the first and second sintering aids exceeds 30% by weight, as in No. 24, the hot strength decreases. Furthermore, sample No. 25.26
If the amount of sintering aid is small, it will decompose and volatilize.

[Phase] When the sintering temperature is low, as in sample No. 27, it is not densified, and when the sintering temperature is too high, as in sample No. 28, it decomposes and volatilizes.

Claims (1)

[Scope of Claims] 1. SiC containing SiC whiskers; a first sintering aid made of one or more selected from oxides of Al, Sc, Y, and rare earth elements; and a periodic table. A second sintering aid consisting of one or more oxides of metal elements belonging to groups VA and VIA, and the remainder, silicon oxynitride or silicon oxynitride consisting of silicon nitride and silicon oxide. Fiber-reinforced ceramics in which a starting material is formed from a product component or a mixture of the two and fired, the composition of each component being 5 to 50% by weight of SiC;
Among them, SiC whiskers are prepared to account for at least 5% by weight or more of the total main components, and the first sintering aid is adjusted to 0.0% by weight.
A fiber-reinforced ceramic characterized in that the content of the second sintering aid is 1 to 25% by weight, and the second sintering aid is 0.05 to 5% by weight.