JPS623074A - Manufacture of silicon nitride base 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 (Field of the Invention) The present invention relates to a method for manufacturing a silicon nitride sintered body, and more particularly, to a silicon nitride sintered body that is homogeneous, has high strength, and has excellent sinterability. Relating to a manufacturing method.

(Prior Art) Silicon nitride sintered bodies are expected to be used as high-strength heat-resistant members, high-corrosion-resistant members, high-temperature high-strength members, etc. because the atomic bonding mode of silicon nitride sintered bodies is mainly covalent bonds.

Conventionally, silicon nitride sintered bodies are densified by liquid phase sintering by adding a sintering aid, but the sintering aid contains Mg.
Oxides of alkaline earth metals such as oxides of alkaline earth metals such as Y2O3, oxides of rare earth metals such as Y2O3, and oxides such as A4z○3 are ground and mixed with these sintering aids and silicon nitride powder to form a silicon nitride sintered body. Served as starting material.

However, the oxide-based additives react with silicon nitride and the 5iOz film present on the crystal surface of the silicon nitride powder to form a grain boundary phase, but even if these raw materials are sufficiently ground and mixed, the additives is not distributed microscopically uniformly, and the size of this grain boundary phase becomes non-uniform.As a result, abnormal growth of silicon nitride sintered grains is promoted, resulting in thick grain boundaries. The phase was the source of destruction. In addition, the addition of oxides increases ionic bonding, and the original excellent properties of silicon nitride are diminished. Therefore, in order to improve the properties of the sintered body, especially the mechanical properties, it is necessary to use a non-oxide sintering aid, reduce the amount of the additive, and disperse it uniformly. .

(Problems to be Solved by the Invention) In order to uniformly disperse such a sintering aid, attempts are generally made to increase the dispersion efficiency by reducing the particle size of the raw material powder and making it ultra-fine. However, when compacted using such pulverized raw material powder, the density of the compact, more specifically the bulk density of the green compact, tends to decrease, and as a result, the sintering Problems such as a decrease in properties, an increase in the amount of shrinkage, a deterioration in dimensional accuracy, and deformation will occur.

To solve this problem, a two-stage sintering method has been proposed in which silicon metal is used as a raw material, a group IIIa compound is added, the silicon metal is sintered in a nitrogen atmosphere, nitrided, and then sintered. Improvements have been made in terms of dimensional accuracy and deformation.

However, according to the above method, metal silicon is nitrided,
The process of modifying α-313N4 to easily sinterable α-313N4 requires several hours to several tens of hours at a sintering temperature of 1400° C. or lower, and therefore is inefficient and impractical in actual production.

Also, non-oxide yarns such as nitride ReN can be used as sintering aids.
(Rθ: Group IIIa metal of the periodic table) has a very high reactivity with moisture, and when handled, it reacts with moisture in the atmosphere and changes from a nitride to an oxide, which ultimately solves the above problems. The current situation is that it cannot be resolved.

(Purpose of the Invention) As a result of repeated research into the above-mentioned problems, the inventors of the present invention have developed a composite nitride that has been nitrided with °C metal silicone IIIa of the periodic table as a sintering aid for silicon nitride a powder. It has been found that a homogeneous sintered body with excellent chemical stability and improved sintering efficiency can be obtained.

Therefore, an object of the present invention is to provide a method for manufacturing a silicon nitride sintered body that can achieve high temperature and high strength characteristics.

Another object of the present invention is to provide a method for manufacturing a silicon nitride sintered body that is easy to sinter and has excellent homogeneity.

(Summary of the Invention) That is, according to the present invention, a composite nitride obtained by nitriding an alloy powder of metallic silicon and a group Za metal of the periodic table is mixed with silicon nitride fine powder as a sintering aid to prepare a raw material. A method for producing a cemented silicon sintered body is provided, which comprises obtaining a composition and sintering it in a nitrogen atmosphere.

(Means to solve the problem) The present invention will be explained in detail below.

According to the present invention, as a raw material composition, a composite nitride of silicon metal-group A metal alloy of the periodic table (hereinafter simply referred to as Si-Ha group metal alloy) is used in Si and sN4 fine powder as an additive. This is very important.

SL-1[[In the group A metal alloy, the Za group metal component itself, which is an additive component, is uniformly dispersed in silicon metal in the form of an alloy. In the present invention, a nitrided alloy is used. Specifically, metal powder obtained by pulverizing an alloy consisting of silicon metal and a single metal of a Ha group element is subjected to a synthesis reaction by a well-known direct nitriding method. It can be obtained by making people do something.

However, direct reaction between metal powder and nitrogen gas generates a lot of heat, so technology to suppress the reaction is required. For example, a synthesis method is mainly used in which the reaction temperature is controlled at 1300 to 1400° C. while controlling the heating rate in the coexistence of hydrogen gas or ammonia gas.

As a result of this reaction, a composite nitride is produced according to the linear formula (1) for Sl-11 [a-group metal alloys]. This nitride is further subjected to a pulverization process to have a particle size of 0.5 to 5 μm and provided as a raw material powder.

In the obtained raw material powder, silicon atoms, group IIIa metal atoms of the periodic table, and nitrogen atoms are not completely crystalline.
It was confirmed by X-ray diffraction that it mainly contained distorted crystalline substances and was in a so-called active state.

Therefore, the present inventor proposed that the metal atoms of group 1 of the periodic table [a] are dispersed in silicon atoms at the atomic level and contain lattice defects, so using such raw material powder together with silicon nitride powder and sintering it in a nitrogen atmosphere. It is believed that when sintered, internal energy greatly contributes to promote sintering, activating diffusion and facilitating sintering, resulting in a high-strength, dense silicon nitride sintered body.

According to the present invention, the product MN according to formula (1) reacts with Sing present on the surface of S''1-sN4 during sintering, and the glass generated in the grain boundary phase of silicon nitride in the sintered body. Since the viscosity of the phase is improved, deterioration of the physical properties of the sintered body at high temperatures is suppressed.

Furthermore, the composite nitride obtained by nitriding alloy powder of Sl-1Wa group metals is extremely stable compared to each element or its nitride, and it is suitable for process control from blending to sintering. There is no need to consider moisture etc. In addition, since the Group 3 metal is uniformly dispersed during compounding, there is no need for super-soaking, so it is possible to prevent a decrease in the bulk density of the compact as a green compact.

According to the present invention, the composite nitride obtained by nitriding the Si-ffa group metal alloy powder can be blended in a desired amount with respect to the silicon nitride fine powder by changing the composition of the composite nitride. However, during sintering, the amount of MN in the composite nitride that acts as an auxiliary agent is required to be at least a specified amount, so it is desirable that the composite nitride be blended at 1% by weight or more in the total raw material powder. . That is, if the amount of composite nitride is unsintered by 1% by weight, the effect of the present invention on sinterability cannot be achieved.

Moreover, the weight composition ratio of Si, -ff1a group metal alloy is S
1: Group IIIa metal is 1:1O to NO:1. Especially 1:
5 to lO: 1 is preferable + <, If the IIIa group metal component is larger than the above range, ■ the oxidation of the a group metal powder will proceed easily and handling will be inconvenient;
If the amount of St exceeds the above range, the effect of the addition of the Za group will be lost and sintering will be difficult to proceed.

This periodic table 1 used in the present invention! [a, group metal atoms include rare earth elements Sc, Y, La, C
e, Pr, Nd, Pm, Sm, 'Fm, C
d, Tb, Iy, Ho, Er, Tm, Yb
, Lu is preferable. Such element 51, for example, silicon nitride raw material powder made by alloying Y with silicon metal and nitriding it is Si, -N -Y
It was confirmed by laser fibremanship and ESCA that it contained either the bond S:L-Y-N or S:L-Y-N.

In the molding process for manufacturing the sintered body of the present invention, any known molding method such as die press molding, cast molding injection molding, extrusion molding, etc. can be used. The sintering step after forming is preferably carried out at a temperature of 1700° C. or higher in a nitrogen atmosphere that does not substantially contain oxygen.

According to the present invention, nitrided Si, -III
In addition to group a metal alloys, At! gos, YzOs,
It is also possible to further add sintering aids such as MgO.

The invention is illustrated by the following example.

〔Example〕

14 after mixing metal silicon powder and rare earth metal powder
An alloy was obtained by melting in a temperature range of 00 to 1600°C. This alloy is pulverized by a well-known method such as Ball Mill/I/ to an average particle size of about 2 μm, and this powder is
A nitriding reaction was carried out in a nitrogen gas atmosphere at 450° C. to minimize the amount of residual silicon.

The obtained lump was coarsely crushed and then finely crushed to an average particle size of 1 μm.
It was set as below. The composition is shown in Table 1.

Next, the obtained nitride, α-S13N 4 and other additives were mixed in the ratio shown in Table 1, and 5isN4
After pulverization, the mixture was molded using a vibrating ball mill, and sintered under the sintering conditions shown in Table 1 to obtain a silicon nitride sintered body.

Further, other additives having an average particle size of 1.0 μm were used.

The specific gravity of the obtained sintered body was determined by the A/Kimedes method and 4-point bending according to JIS R1601 (test piece:
The bending strength was measured by 4 X 3 X 42 IIIar).

As a result of the measurement, as is clear from Table 1, the ratio J1. Both strengths showed high values.

Comparative Example In the example, nitrided Si as an additive,
- Instead of IEra group metal alloys, grain size 1. Q/J#
1 YtOs, 1 Ultos, YN, were prepared based on Table 1 to obtain sintered bodies Todoroki 6 to &8.
Characteristics were measured in the same manner. The results are shown in Table 1.

As is clear from Table 1, both the specific gravity and strength were inferior to those of the present invention.

(Effects of the Invention) According to the manufacturing method of the present invention, by using a nitrided SL-ff1a group metal alloy for the α-8i, 3N4 Saka powder, it is possible to prevent moisture etc. during powder preparation. It is not necessary to take this into consideration, and it is possible to obtain a homogeneous and high-strength sintered body without reducing the density during molding, and it is also possible to improve the ease of sintering.

Claims (1)

[Claims] A composite nitride obtained by nitriding an alloy powder of metallic silicon and a group IIIa metal of the periodic table is mixed with silicon nitride fine powder as a sintering aid to obtain a raw material composition, which is sintered in a nitrogen atmosphere. A method for manufacturing a silicon nitride sintered body, characterized by: