JPS6256367A - 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] Invention! Description [Field of Application of the Invention] The present invention relates to a silicon carbide sintered body, particularly a tough silicon carbide sintered body suitable for use as a heat-resistant structural member.

[Background of the invention]

Sintered silicon carbide is a material with excellent oxidation resistance, chemical stability, hardness, and strength. However, these properties also vary depending on the sintering aid.

For example, boron-based sintering aids generally have low room temperature strength due to problems such as free carbon remaining in the sintered body and large grain growth. On the other hand, in aluminum-based materials, ktzo3 reacts with the surface of silicon carbide powder and remains in the structure, resulting in a decrease in high-temperature strength.

Also. There is also a patent in which Y2O3, especially among group oxides, is added in an amount of ZOwt% and sintered at 1800t:'. (
JP 48-32110). Further Y2O3 for 25~4Q
A method of obtaining a silicon carbide sintered body by adding wt and sintering SiC at a relatively low temperature of 1850C to 1900C has also been proposed (JP 51-568151°) However, in both cases, the sintering temperature is Sufficient strength cannot be expected because the sintering temperature is lower than that of SiC, the former has too little Y2O3 and it is difficult to achieve uniform, dense sintering, and the latter has a large amount of Y2O3, so S
There were drawbacks such as the loss of the original properties of iC.

In addition, the ease with which SiC grains grow during sintering varies depending on the sintering method. In general, grains grow easily in the non-pressure sintering method, and the crystal grain size of the sintered body increases, making it difficult to obtain sufficient strength. Hard to obtain.

[Purpose of the invention]

An object of the present invention is to provide a silicon carbide sintered body that has high strength from room temperature to high temperature and particularly high fracture toughness.

[Summary of the invention]

The sintered body of the present invention is characterized by having fine crystal grains mainly composed of silicon carbide and containing swt% to 20wt% of Y2O3 or La5hs. This sintered body can be easily manufactured by the real press method. Furthermore, preferably by dispersing a metal carbide other than SiC in this sintered body.

It is characterized by a particularly strong sintered body.

As a result of extensive studies by the present inventors, we found that by using the hot press method, a material with a Y2O3 or Lat,s content of 5 wt% to 2 Qwt% has a sufficiently dense structure with an average grain size of 2 μm or less. It has been found that a silicon carbide sintered body can be obtained. This sintered body is not only strong but also
There is little decrease in strength even in Gaomu.

The latter reason is that Y203 and La2O3 themselves, which are present as sintering aids in the sintered body, have the effect of suppressing the grain growth of SiC and the effect as a sintering aid; This is thought to be due to its excellent mechanical properties even at high temperatures.

% was added to form YzOs in the tissue.
When the addition form of Y element is Y metal or Yf4x (X is an integer), and when it is added as L, a metal or LaHr (X is an integer) to form LazOa'&, the strength decreases even more at high temperatures. There are fewer of them. This is Y
, YHx, L a , and L a Hx when sintered, Y and L a will form Y2O in the structure of the sintered body.
It exists as a simple substance of 3 and Lavas, but Y2O.

When added in the form of oxides such as La20M and
7 licates such as Os.5iOz are generated, which is thought to cause deterioration of high-temperature properties.

On the other hand, considering the reason for the former's strong
Since the coefficient of thermal expansion of 5SiC and LazOs below 1oooC is larger than that of SiC, strain stress is generated during the cooling process after sintering during assembly of 5SiC, which increases the energy for the progression of fracture. .

It is thought that it has become tougher.

In this way, the presence of Y2O3 and La2O3 immediately
It is effective in strengthening the steel and preventing strength loss at high temperatures.

However, the si amount of Y2O3 and La2O3 is 5 Iv t
If S is not +'fite, sintering tends to be insufficient, and a sintered body with sufficiently high strength cannot be obtained. On the other hand, when Y2O3 or Latos in one structure exceeds 20wt, there is almost no decrease in strength, but the toughness value decreases significantly and Si
What are the characteristics of C? This means that the rotation of SiC particles is Y2
In order for O3 and La2O3 to become surrounding, Y2O
It is thought that the properties of 3 and LazOs made it hard and brittle. Note that the average grain size of the sintered body is 2μ
It is necessary that it is less than m.

If the particle size exceeds this range, not only the strength will decrease, but also the toughness will decrease, and the sintered body will not have sufficiently high reliability.

vcK, this carbonized @ cable sintered body is sintered by adding metal element or hydride powder that becomes carbide in the sintering process, and S
Metal carbide particle aggregates such as metal carbide particles other than iC bonded with Y2O3 may be dispersed in the structure, or carbide may be directly added to the structure. It is thought that the fracture toughness value was improved by causing branching of the crank. The abundance of these metal carbides is 6 to 3
A range of 0 wt is desirable, and if it is less than this, there will be no sufficient effect in improving the fracture toughness value. In addition, if the amount is too large, sinterability deteriorates and strength and oxidation resistance decrease.

Note that the metal carbide to be dispersed is T, which is stable in SiC.
A carbide such as ``pvt''*Z r t N b is preferable.

[Embodiments of the invention]

Examples will be described below.

Example 1 Mainly SiC powder with a particle size of 0.7 μm, and Y2O3 containing YH2 powder with a particle size of 1 to 10 μm as a sintering agent.
Converting to 2. ．． 5 to zswtl was weighed and blended. To this was added silicone 15Vo1% as a binder, and after mixing using a sieve machine, the mixture was sieved using a 167 mm sieve. Next, this was placed in a mold and molded into a disk shape of 60φxiot at a molding pressure of 500 Kf/i, and the molded body was placed in a graphite mold and hot press sintered. At this time, the pressure is 30
04/i and 2050C at a heating rate of 20 to 40C/min.
In order to prevent the crystal grains of the sintered body from coarsening when the temperature was raised to ~2200℃, a temperature filter was used that cooled the sintered body immediately at the same speed without holding it at the sintering temperature after reaching a predetermined temperature.

The average crystal grain size of the obtained sintered body was 0.8 to 2. Oltm
It was a minute thing. on the other hand.

As a comparative example, the crystal grain size of a sintered body added with 3 wt % of Y203 and sintered by a pressureless method was as large as 3 to 5 μm.

#J image formation et al.4wX3HX obtained by Hontopress method
A prismatic sample 2 of 45 tm was prepared, and the four-point bending strength at room temperature and at a specified temperature was determined. Fracture toughness value Kh (MN/m) 5r: was determined from the bending strength σ of the sample with the laminate using the formula (I).

Soil - K 1 @ ~1.2×σXS4
......(1) Next, %Y2O3 and bazo
Using s content of 1Qwt and 15wt%, σb4 was determined at each temperature, and changes in characteristics at high temperatures were studied. In addition.

As a comparative example in this case, the results of a SiC sintered body sintered using AtN as an auxiliary agent are shown.

Figure 1 shows σb for Y2O3 and La2Q3 contents.
Figure 2 shows the temperature change of σb4.

From Figure 1, if the YzOs content is less than 5wt, σb4
1 Ki * both become small values, and when the weight exceeds 20 wt, only 1 degree decreases rapidly. This tendency is Lag
's is the same. From these results, Y2O5 and L
When the ag's content ranges from 5 to 20 wt%, a sintered body with excellent properties is obtained, and K1. is 8 MN/m”
reach more than that.

From FIG. 2, it can be seen that the S i C sintered body containing Y2O3 or Lag's does not deteriorate in strength even at high temperatures, compared to AtN. In addition, Y2O3 obtained by pressureless sintering method
The soil KIm of 8 wt% #j average particle diameter (3-5 ttm) is 2.0-2. ．． It was 5MN/m'.

Example 2 The content of Y2O3 or L azU3 in the SIC sintered body was 15 wt% in S i C powder with the same particle size as in Example 1.
Y Hs was added by weighing so as to be constant, and the amount of V or '1'i was added and sintered7, and the carbide particle aggregate of 'ri' or V was dispersed during the assembly. A sintered body was obtained, and these σh4. kQe was calculated.

(Figure 3) Furthermore, when the volume fraction of riC is kept constant at 15.0vo11, the change in 1 g at high temperature is determined, and 'f: i C1 sintered with AtN2wt1.
5. Qvo 1% SiC sintered body is also shown for comparison.

Figure 3 shows that a sintered body with excellent properties can be obtained when the volume fraction of the metal carbide ranges from 6 to 30 vol.
It can be seen that the temperature characteristics are immediately 6.

Example 1 A sintered body was produced in substantially the same manner as in Example 2, mainly using SiC powder having the same particle size as in Example 2.

In this example, there are two types of additive metals (Tj, V) that form the metal carbide, and the amount of the added metals is constant at 15vo1% in total of the two metals.

A study was conducted by changing the ratio of s'17 r and V within this constant volume ratio range. FIG. 5 shows the ratio of +f i to V at room temperature of 1. This is what is shown. 1. The amount of (2) is especially large in the range of 50 to 9 Qvol of the total lid of +rH and V. is obtained. This is thought to be due to the coexistence of 'ri, :V, which forms a double carbide of fi and V during the sintering process, and the uniformity changes depending on this composition.

〔Effect of the invention〕

According to the present invention, it is possible to obtain a silicon carbide sintered body whose fracture toughness and strength are not only strong at room temperature but also high even at high temperatures, and this sintered body can be used as a highly reliable heat-resistant structural member.

[Brief explanation of the drawing]

1 to 5 are curved fan diagrams showing the effects of the embodiment of the present invention.

Claims (1)

[Claims] 1. Yttrium or lanthanum oxide from 5 wt% to 2
A silicon carbide sintered body containing 0 wt% and having a structure of the sintered body having an average grain size of 2 μm or less. 2. A silicon carbide sintered body according to claim 1, characterized in that an elemental metal or a metal hydride is used as a raw material for yttrium or lanthanum. 3. A silicon carbide sintered body, characterized in that a metal carbide other than silicon carbide is dispersed in the sintered body according to claim 1 or 2.