JPS63103867A - Manufacture of silicon nitride base sintered body - 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 (Field of the Invention) The present invention relates to a method for manufacturing a silicon nitride sintered body.
More specifically, the present invention relates to a method for producing a homogeneous and high-strength silicon nitride sintered body.

(Prior Art and its Problems) 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 bonding.

As is well known, silicon nitride sintered bodies are densified through liquid phase sintering by adding a sintering aid, but what about the sintering aid? '
There are oxides of alkaline earth metals such as 1gO, oxides of rare earth metals such as Y2O3, and AIzOz, etc. These sintering aids and silicon nitride powder are ground and mixed and used as a starting material for silicon nitride sintered bodies. There is.

However, the oxide-based additives react with silicon nitride and the SiO□ film present on the crystal surface of silicon nitride powder to form a grain boundary phase, but even if these raw materials are thoroughly mixed and pulverized, , the additives do not have a microscopically uniform distribution, 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 a large thickness. The grain boundary phase was the source of the fracture. In addition, the addition of oxides increases ionic bonding, and the original excellent properties of silicon nitride are diminished. Therefore, the properties of the sintered body,
In particular, in order to improve mechanical properties, it is necessary to use a non-oxide sintering aid, reduce the amount of the additive, and uniformly disperse the additive.

In order to achieve uniform dispersion of such sintering aids, attempts are generally made to increase the dispersion efficiency by reducing the particle size of the raw material powder and making it into ultra-fine powder. When molded using raw material powder, the density of the molded product, more specifically, the bulk density of the green compact, tends to decrease.
Accordingly, problems such as a decrease in sinterability, an increase in the amount of shrinkage, a deterioration in dimensional accuracy, and deformation occur.

(Structure of the Invention) The present inventors used a sintering aid for a fine alloy powder consisting of metallic silicon and a group Ia metal of the periodic table, or a nitride obtained by nitriding a fine alloy powder thereof. It has been found that a silicon nitride sintered body exhibiting high temperature and high strength can be obtained when the mixture is mixed and molded and fired in a nitrogen atmosphere.

That is, a silicon nitride sintered material is produced by molding a fine alloy powder made of metallic silicon and a group MA metal of the periodic table, or a mixture of its nitride and a sintering aid, and sintering it in a nitrogen atmosphere. A method of making a body is provided.

The present invention will be explained in detail below.

Direct nitriding of silicon, silica reduction, vapor phase synthesis, and thermal decomposition are generally known methods for producing raw material powder for silicon nitride sintered bodies, and these are currently the most widely used industrially. This is the direct nitriding method of silicon. This method uses silicon metal powder and nitrogen gas to form 3Si+2Nz-5itN
It is characterized in that the reaction is simple and the manufacturing process is relatively simple.

According to the present invention, as one of the raw material powders for a silicon nitride sintered body, a group ma metal of the periodic table, which is to be used as a sintering aid for a silicon nitride sintered body, is added to silicon metal in a silicon direct nitriding method. It is important to use an alloy containing the simple substance of . The alloy is manufactured by mixing metallic silicon powder and powder of a group MA metal of the periodic table, for example, from 1400 to 1
This is done by heating to a temperature of 600°C to melt.

The obtained alloy is pulverized using a pulverizer such as a ball mill to form a fine powder having an average particle size of 0.5 to 10 μm.

Rare earth elements Sc, Y, La, Ce, Pr are metal atoms of Group 1IIa of the periodic table used in the present invention.
, Nd, Pm, Sm, Eu, Gd, Tb, Dy, I(o
+Er, Tm, Yb, Lu or a combination thereof is desirable.

In this alloy, silicon metal powder and ma
Group metals vary depending on the type of use of the alloy, but 99
．． It is desirable to use a weight ratio of 9:0.1 to 70:30, particularly 99.5:0.5 to 90:10. That is, if the amount of Group Ma metal of the periodic table is less than the above range, it is difficult to uniformly distribute the sintering aid in an effective amount, whereas if it is more than the above range, silicon nitride The excellent properties of the quality sintered body will be lost.

According to the present invention, the alloy thus obtained is once nitrided to form a composite nitride, and then sintered again or used after being nitrided during the sintering process. This nitriding reaction proceeds as shown in the formula %, where h represents the group ma metal of the periodic table. During this nitriding process, direct reaction between the metal powder and nitrogen gas generates a large amount of heat, so a technique 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 temperature in the coexistence of hydrogen gas or ammonia gas.

Next, after the reaction synthesis, a pulverization step is introduced as necessary to provide a composite nitride as a raw material powder for a sintered body.

When the temperature of the nitriding reaction is within the above range, a composite nitride mainly composed of α-3i3N4 is produced, but at a temperature higher than the above temperature, a composite nitride mainly composed of β-3i3N is obtained.

The composite nitride mainly contains α-5i3N4, and also contains metallic silicon and a group ma metal of the periodic table in the above-described quantitative ratio in terms of elements.

Therefore, based on the examples described later, the inventors believe that metal atoms of group M of the periodic table are dispersed in silicon atoms at the atomic level and contain lattice defects, so that when sintered using such raw material powder, It is believed that internal energy makes a large contribution to promoting sintering, activating diffusion and facilitating sintering, and as a result, a high-strength, dense silicon nitride sintered body is provided.

Furthermore, in the composite nitride according to the present invention, simple Si3N,
Since the scattering intensity ratio of MN is lower than the X-ray scattering intensity ratio of each compound observed in a mixture of For example, silicon nitride raw material powder made by alloying Y with silicon metal and nitriding it is presumed to contain either 5t-N-Y or 5i-Y-N bonds. be done.

According to the present invention, a sintering aid is added to and mixed with the aforementioned fine alloy powder or composite nitride thereof, and the mixture is shaped and fired in a nitrogen atmosphere.

As the sintering aid to be used, those known as sintering aids for silicon nitride can be used.

For example, 81□O,, MgO, 8IN, B4. In addition to C, Y
Examples include oxides, nitrides, Be compounds, and Zr compounds of group ma elements of the periodic table such as zOi and YN.

In this way, by adding a sintering aid to an alloy of metallic silicon and a group MA metal of the periodic table or a composite nitride thereof and firing the alloy, it is possible to lower the sintering temperature, and further increase the sintering temperature. It is possible to improve the strength at room temperature.

In one embodiment of this firing method, a mixture of a composite nitride and a sintering aid is molded, and this molded product is fired at a temperature higher than the nitriding temperature.

As the sintering aid, any of the aforementioned sintering aids may be used alone or in combination of two or more. These sintering aids are preferably used in amounts of 0.1 to 10% by weight, particularly 1 to 5% by weight. That is, when the amount of the sintering aid exceeds 10% by weight, the original objective of improving the heat resistance of the grain boundary phase can be achieved, and when it is less than 0.1% by weight, it is not effective as an aid (
Become.

Molding and firing may be performed in this order or simultaneously. The shaping can be carried out, for example, by methods known per se,
For example, the mold press molding method, cast molding method, injection molding method, extrusion molding method, etc. can be used, and the sintering of the molded body is
It can be carried out at a temperature of 700 to 2100° C. for 0.5 to 10 hours. When molding and sintering are performed simultaneously, the firing may be performed within the above temperature range and on the lower side of the above conditions using, for example, hot pressing or hot isostatic pressing. Further, sintering is preferably performed in a nitrogen atmosphere.

In another embodiment, the fine alloy powder is mixed with the sintering aid without being nitrided and then molded. Next, the obtained compact is once nitrided at 1300 to 1400°C to produce a composite nitride containing a sintering aid, and if desired, the temperature is further raised continuously in a nitrogen atmosphere to a temperature of 1100 to 1400°C. Firing is carried out at a temperature of 1450°C. Further, if necessary, by sintering this sintered body at a high temperature, a dense sintered body with excellent properties can be obtained. According to this method, the blending amount of the sintering aid may be set within the range of the first embodiment described above on the premise that the alloy fine powder becomes a composite nitride.

The invention will now be explained with the following examples.

Example 1 Metallic silicon powder and a Group Ma element of the periodic table were weighed and mixed at the blending ratio shown in Table 1 to obtain a powder of 1400-16
An alloy was obtained by melting in a temperature range of 00°C.

This alloy was milled using a well-known method such as a ball mill to obtain an average grain size of 2.
Grind this powder to about 1100 to 1450 μm.
A nitriding reaction was carried out in a nitrogen gas atmosphere at a temperature of 0.degree. C. until the residual silicon became 0.3% or less. The obtained lump was coarsely pulverized and then finely pulverized to obtain a composite nitride having an average particle size of 1 μm or less.

The obtained composite nitride was mixed with a sintering aid shown in Table 1 at a predetermined ratio and then molded, and then fired under the firing conditions shown in Table 1 in a nitrogen atmosphere.

When the bending strength and specific gravity of the sintered body thus obtained were measured, the results shown in Table 1 were obtained. The bending strength is JISR1
4 x 3 x 42m by 4-point bending test method according to 601
It was determined by measuring the bending strength of a test piece of m.

Comparative Example One of Yz(h, Alz(h, YN) was mixed into silicon nitride fine powder based on Table 2, and the firing conditions were as shown in Table 2.
A sintered body was produced and its properties were measured in the same manner as in Example 1.

As a result of the measurement, both were inferior in specific gravity and strength compared to the present invention.

Example 2 The fine alloy powder produced in Example 1 was mixed with the sintering aid shown in Table 3 without nitriding, and then molded.
After nitriding in a nitrogen atmosphere at a temperature of 400 to 1,600°C to produce a compact made of composite nitride containing a sintering aid, the temperature is further increased and firing is performed under the conditions shown in Table 3. Obtained a body.

The properties of the obtained sintered body were measured in the same manner as in Example 1, and the results shown in Table 3 were obtained.

As is clear from Table 3, a sintered body with excellent characteristics was obtained even when compared with the comparative example shown in Table 2.

(Effects of the Invention) According to the method for producing a silicon nitride sintered body of the present invention, a sintering aid is added to an alloy powder of metallic silicon and a group MA metal of the periodic table or a composite nitride thereof as a raw material powder. By adding and firing, it is possible to increase the ease of sintering and lower the firing temperature required for densification.

Furthermore, as a sintered body, the strength, especially the bending strength at room temperature, can be increased.

Claims (1)

[Claims] A silicon nitride sintered body, characterized in that a fine alloy powder consisting of metallic silicon and a group IIIa metal of the periodic table or a mixture of a composite nitride thereof and a sintering aid is molded and fired in a nitrogen atmosphere. manufacturing method.