JPH03218972A - Silicon nitride-based sintered body - Google Patents

Abstract

PURPOSE:To attain high denseness without using a hot press and to improve strength and oxidation resistance at high temp. by specifying the amts. of the oxide of a rare earth element, a vanadium component and silicon nitride. CONSTITUTION:This silicon nitride-based sintered body is formed with a compsn. consisting of 1-20wt.% oxide of a rare earth element for accelerating sintering, 1-8wt.% (expressed in terms of V2O5) vanadium component and the balance silicon nitride. A dense body is easily obtd. by the vanadium component and vanadium silicide is formed at the grain boundaries in the resulting sintered body to improve the strength.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a silicon nitride sintered body that has high high temperature strength and excellent oxidation resistance.

<Prior art> Silicon nitride sintered bodies have excellent properties such as mechanical strength, heat resistance, and corrosion resistance, so they are used in high-temperature structural materials such as automobile engine parts and gas turbine engines. is being attempted.

Since this silicon nitride has a high covalent bonding property, it is difficult to sinter it alone, so MgO, A 12 t (h. Zroz
Sintering has been carried out by adding sintering aids such as oxides of rare earth elements.

<Problems to be Solved by the Invention> In the above conventional technology, Mgo. A Il 20s
When metal oxides such as , ZrO, etc. are used as sintering aids, a low melting point glassy phase precipitates in the grain boundary phase, which inhibits the improvement of strength at high temperatures and inhibits the improvement of oxidation resistance. Was.

In addition, when rare earth element oxides are used alone as sintering aids, they have a poorer sintering promoting effect than other sintering aids, so
Real pressing is necessary to obtain a dense sintered body. Therefore, we conducted various studies on sintering aids, and found that they have excellent sinterability to the extent that densification can be achieved without using hot pressing, and that they have better high-temperature strength and acid resistance than when using conventional sintering aids. The development of a silicon nitride sintered body with excellent oxidation properties is desired, and the present invention aims to provide such a sintered body.

<Means for Solving the Problems> The present invention has been made as a result of various studies to achieve this object, and its outline is that one or more oxides of rare earth elements are
~20% by weight, a total of 1 to 8% by weight of the vanadium (V) component in terms of v20, and the balance is silicon nitride (St, N,)
It is a silicon nitride sintered body consisting of.

<Function> Here, rare earth element oxides are used to promote sintering.
It is added in an amount of up to 20% by weight, but if it is less than 1% by weight, it will not have the effect of promoting sintering, and if it exceeds 20% by weight, the mechanical strength of the sintered body will decrease. Also, when the amount of rare earth element oxide added is increased, the temperature rises from 700 to 1000℃
melilite-type compounds (RzS) that are harmful to the low-temperature oxidation of
Since a large amount of iaOJ4 (R: rare earth element) is produced and the oxidation resistance is lowered, the amount added is preferably 15% by weight or less.

Next, the V component is an oxide that is effective as a sintering aid, and a dense body can be easily obtained using sintering methods other than hot pressing, such as gas pressure sintering, which makes it difficult to create products with complex shapes. . In addition, by adding these components, oxygen is released into the sintered body and a melilite type compound (R, Si.0
, N4) and VSi2 and V5S at the grain boundaries.
Silicides such as i3 are formed. These silicides have a melting point of 1
The temperature is extremely high at 600°C or higher, and a sintered body in which this is generated at the grain boundaries has almost no decrease in strength even at high temperatures. Furthermore, by uniformly dispersing this silicide in the grain boundaries, SiJ. It also has the effect of suppressing particle growth and improving mechanical properties. When V20 is less than 1% by weight, it has no effect as an auxiliary agent or suppresses the formation of melilite-type compounds, and on the other hand, when it exceeds 8% by weight, V silicide becomes excessive.
Since it is not uniformly dispersed and aggregates, the room temperature strength and high temperature strength decrease, which is not preferable.

Example 1 α-Si3N. with an average particle size of 0.7μ. The powder had y, o. , ■20, with an average particle size of 1μ, and each powder with an average particle size of 1μ1〇A j2 zCh were blended in the proportions shown in Table 1, mixed and pulverized in a ball mill, and then 200 kg / d - 1800 ° C - with a honoto press. Sintering was performed for 1 hour to obtain a sintered body measuring 35 x 35 x 5 m. The properties of the sintered body were measured by the following method, and the results are shown in Table 1.

(1) Flexural strength JIS-2 at room temperature and 1300℃
Three-point bending strength according to R 1601 and JIS-R 1604, (2) Oxidation weight gain: After oxidation for 100 hours each in the air at iooo°C and 1350°C, the weight increase was measured (3X
4X35fi specimen) From the results in Table 1, it is clear that the hot-pressed sintered body (Ncil, 2) obtained according to the present invention has an extremely small decrease in strength from room temperature to 1300°C, and has a strength of 90% at 1300°C.
It exhibits high strength of over 1,000 kg/w''.Also, in terms of oxidation properties, the oxidation weight gain is 0.
It is extremely small, less than 1 .mu./cd, and has excellent oxidation resistance.

On the other hand, in llh3 shown as a comparative example, the strength at 1300°C was significantly lower than the room temperature strength due to the formation of a low melting point glass phase at the grain boundaries due to the addition of Al,03.
In 1h4, melilite phase is formed by adding only Y20, 1
The oxidation weight gain at 000°C increased significantly and the oxidation resistance decreased.

Table 1: Properties of photo-press phosphorus bodies Example 2 Using the same raw material powder as in Example 1 and rare earth element oxide with a purity of 99.9%, the powders were mixed in the proportions shown in Table 2 and dried. 10 x 10 x 5 at a pressure of ton/1 (
BS using a hydrostatic press, and gas pressure sintering was performed under the conditions shown below to obtain a sintered body. The relative densities of the sintered bodies are shown in Table 2.

Firing conditions: Nt 5 atm - 1900°C 2 hr A dense sintered body with a density of 98χ or more could be obtained. However, as shown in Comparative Examples (Nos. 10 to 13), if Shys is less than 1% by weight or rare earth element oxide is less than 1% by weight, it has no effect as a sintering aid, and the resulting sintered The compact had a low relative density of 80 to 85χ, and open pores remained.

Table 2 Sinterability by gas pressure sintering Example 3 (Characteristics of gas pressure sintered body) Using the same raw material powder as in Example 2, the powder was mixed in the proportions shown in Table 3 and dried at 2 tons/cm2. 50x5 at the pressure of
A sintered body was obtained by molding to 0xlOW using a hydrostatic press and performing gas pressure sintering under the following conditions. The properties of the sintered body were measured by the following method, and the results are shown in Table 3.

Sintering: Gas pressure sintering (two-stage sintering) Primary firing: 1N, medium 2 atm-1800℃-2hr Secondary firing: N2 medium 100at+n-1800℃-2hr (1)
Flexural strength: JIS-R 16 at room temperature and 1350°C
01 and JIS-R 1604, 3-point bending strength (
2) Oxidation weight gain: Weight gain was measured after oxidation at 1000°C and 1350°C in the air for 100 hours each (3 x 4
As shown in Table 3, the gas-pressure sintered bodies (floors 14 to 22) obtained according to the present invention showed extremely small decrease in strength from room temperature to 1300°C, and had a strength of 79 kg at 1300°C.
Shows high strength of /w2 or more. Also, in terms of oxidation properties,
The weight gain due to oxidation is very small, less than 0.2 μ/d at both 1000°C and 1350°C, and it has excellent oxidation resistance.

On the other hand, I1m23-5 shown as a comparative example has a small ν20 and a rare earth element oxide of less than 0.1 weight χ, so there is no effect of adding it as an auxiliary agent, so it does not become densified, and has poor strength and oxidation resistance. Both are inferior to the product of the present invention.

On the other hand, in case 26, the amount of V20 added is 10 weight χ, which exceeds the 8 weight χ within the scope of the present invention, so V silicide is excessive.
The strength at room temperature and at 1300°C is significantly lower than that of the product of the present invention. Furthermore, since Arashi 27 has a large amount of rare earth element oxide added, a melilite type compound is formed, and the oxidation resistance at 1000° C. is significantly deteriorated, and the room temperature and high temperature strength are also inferior to the examples.

Example 4 Same raw material powder as Example 1 and Cr20 with an average particle size of 1 μ-
3, blended in the proportions shown in Table 4, and dried the powder at a pressure of 2 ton/cd in a size of 10 x 10 x 50 m.
The sintered body was molded using a hydrostatic press, and gas pressure sintered under the conditions shown below to obtain a sintered body. The cross section of the sintered body is mirror polished and S
Tissue observation was performed based on the composition of EM. Photographs of this structure are shown in Fig. 1-A (Example) and Fig. 1-B (Comparative Example).

Firing conditions: 2 N2 medium 10 ats-1850℃-4 hr
Table 4 In the microstructure photographs shown in Figure 1-A (Example) and Figure 1-B (Comparative Example), the white bright spots are silicides of V and Cr, and the black-gray columnar particles are Si. N. , the white part surrounding it is the grain boundary phase of the Y compound.

According to this, in the example, V silicide of 1μ or less steel is uniformly dispersed, and Si3N. Grain growth of particles is suppressed. On the other hand, in the comparative example, Cr silicide and Si3N
．． The particles have grown significantly compared to the examples, and the room temperature bending strength of the sintered bodies of the comparative examples is also inferior to that of the examples. (See Table 4) By adding v20 in this way, Si3N.
It also has the effect of suppressing particle growth and improving mechanical properties.

<Effects of the Invention> According to the present invention, by adding appropriate amounts of rare earth element oxides and component can provide cohesion.

[Brief explanation of drawings]

Figure 1-A shows the example, and Figure 1-B shows the comparative example.
This is an S-EM photograph showing.

Claims (1)

[Claims] A silicon nitride sintered body comprising 1 to 20% by weight of one or more oxides of rare earth elements, 1 to 8% by weight of a vanadium (V) component in terms of V_2O_5, and the remainder silicon nitride (Si_3N_4).