JPS6340767A - Silicon nitride sintered body and manufacture - Google Patents

Abstract

(57) [Abstract] 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 high-density and high-strength silicon nitride sintered body and a method for manufacturing the same.

[Conventional technology]

Silicon nitride sintered bodies have traditionally attracted attention as one of the ennobling ceramics used in high-temperature structural members, but silicon nitride alone is difficult to sinter, so
Sintering is performed using a low melting point compound as a sintering aid. As such sintering aids, oxides of aluminum, magnesium, yttrium, lanthanum, cerium, beryllium, zirconium, etc. are known, and a method in which one or more of these are added and sintered is common.

However, even if sintering is performed with the addition of the above-mentioned sintering aid, it is not sufficient to obtain a high-density, high-strength silicon nitride sintered body, and pressure sintering such as a hot press method is required. Because of this, continuous sintering is difficult and the product has disadvantages such as high cost.

Furthermore, the use of a combination of norconium oxide and aluminum oxide as a sintering aid in the production of silicon nitride sintered bodies has already been considered (Inomata et al., Ceramics Association Journal 82α2
1, 1976). However, in this report, the characteristic values of the obtained silicon nitride sintered body are not shown, but since ordinary monoclinic zirconium oxide is used as the zirconium oxide, the crystals of zirconium oxide in the sintered body are Judging from the shape, it was expected that the properties would deteriorate due to phase transformation of norconium oxide, and in fact, the inventors' experiments confirmed the above-mentioned property deterioration.

[Problem that the invention seeks to solve]

In view of the above circumstances, the present invention aims to provide a high-density and high-strength silicon nitride sintered body by selecting an optimal sintering aid, and to pressurize by using the optimal sintering aid. It is an object of the present invention to provide a method for producing a silicon nitride sintered body that can produce a sintered body with high density and high strength not only by sintering but also by pressureless sintering.

[Failure to solve the problem]

The silicon nitride sintered body of the present invention contains 3 to 20% cubic zirconium oxide and 1 to 1% aluminum oxide.
0% by weight, 1 to 15% by weight of yttrium oxide, and the remainder silicon nitride, and most of the silicon nitride is in the β phase.

The above-mentioned method for producing a silicon nitride sintered body uses stabilized cubic zirconium oxide powder in an amount such that the content in the produced sintered body is 3 to 20% by volume, and 1 to -10% by weight of aluminum oxide. powder, 1 to 15% by weight of yttrium oxide powder, and the balance of silicon nitride powder are added and mixed;
After the mixed powder is pressure-molded, it is sintered at 1700 to 1900C in a non-oxidizing gas atmosphere, and sintering may be performed not only by pressure sintering but also by normal pressure sintering.

Zirconium oxide is normally in the monoclinic form, but in this method, zirconium oxide is stabilized in the cubic form. For this purpose, monoclinic zirconium oxide is heated to about 1000 tr with at least one element of calcium oxide or magnesium oxide, or an oxide of a group LA metal, especially yttrium oxide, to produce zirconium oxide stabilized in cubic crystal form. is obtained.

[Effect]

In the present invention, it is important to use stabilized cubic zirconium oxide as a sintering aid in combination with aluminum oxide and yttrium oxide. especially,
By using stabilized cubic zirconium oxide, there is no phase transformation at the sintering temperature, and a silicon nitride sintered body with excellent properties can be obtained.

The reason why the amount of norconium oxide added is limited to 3 to 20 parts by volume is that if it is less than 3 parts by volume, the silicon nitride sintered body will not have the effect of improving density or strength, and if it exceeds 20 parts by volume, silicon nitride sintered This is because the strength of the solid body is significantly reduced.

Furthermore, Rizan limits the amount of aluminum oxide and yttrium oxide added to 1 to 10% by weight and 1 to 15% by weight, respectively. This is because, in particular, it causes a significant decrease in high-temperature strength.

〔Example〕

Example 1 The average grain size was set to 1 to have the composition of the sintered body shown in Table 1 below
α-8i3N4 powder of less than μm size, Y2O3-stabilized cubic ZrO2 powder, A[203 powder and Y2O3 powder were mixed, and the mixed powder was statically pressed at a pressure of 1 ton/cm2. 6 mm x 6 mm from this molded body
The molded body cut into a size of 40 mm was sintered at a temperature of 1800° C. for 2 hours in a nitrogen gas atmosphere of 2 atm.

Table 1 1 Remainder 1 vr) 9% l wt%
1wt%2 Remainder 5 3 33
Remaining portion 5103 4 Remaining portion 5315 5 Remaining portion 1033 6 Remaining portion 1055 7 Remaining portion 2555 8 Remaining portion 0 3 39
Remainder 0 5 510 Remainder
5 0 511 Remainder 5
5 012 Remainder 3
5 513 Remainder 10 15
514 Remainder 10 5 2
0 Density (chi), hardness (HRA) of each sintered body obtained
) and transverse rupture strength (ky/mm2) and the results are shown in Table 2 below.

Table 2 (Note) Samples AI, &7 to 14 are comparative examples.

Example 2 Sintered bodies were manufactured under the same conditions so as to have the same composition as the sintered bodies of sample numbers A 2 , 5 , and 6 of Example 1, but using monocrystalline powder, and each of the obtained sintered bodies Density (%), hardness (HRA), transverse rupture strength at room temperature (ky/mx
2) and fracture toughness (MN/m3/2) are shown in Table 3 below.

Table 3 Sample shop Density Hardness Transverse rupture strength Fracture toughness 2 98
92 85 5.25 97 91
80 5.56 98 90 85
5.82*94 88 55 4
．． 55*95 90 65 4.76"
96 90 70 4.9 (Note)
Samples A 2 , 5 and 6 are comparative examples.

〔Effect of the invention〕

According to the present invention, a silicon nitride sintered body having high density, high hardness, high strength, and excellent toughness can be provided at low cost.

Therefore, this silicon nitride sintered body is expected to be applied to wear-resistant parts such as automobile parts and cutting tools.

Claims (3)

[Claims] (1) A silicon nitride sintered body comprising 3 to 20% by volume of cubic zirconium oxide, 1 to 10% by weight of aluminum oxide, 1 to 15% by weight of yttrium oxide, and the balance silicon nitride. (2) stabilized cubic zirconium oxide powder in an amount such that the content in the generated sintered body is 3 to 20% by volume, 1 to 10% by weight of aluminum oxide powder, and 1 to 1% by weight of aluminum oxide powder;
Nitriding, which is characterized by adding and mixing 5% by weight of yttrium oxide powder and the remainder of silicon nitride powder, press-molding the mixed powder, and then sintering it at 1700 to 1900°C in a non-oxidizing gas atmosphere. Method for manufacturing silicon sintered body. (3) Cubic zirconium oxide includes calcium oxide,
The method for producing a silicon nitride sintered body according to claim (2), which is stabilized by heating with at least one of magnesium oxide and yttrium oxide.