JPH0633174B2 - Method for manufacturing silicon nitride sintered body - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for producing a silicon nitride sintered body, and more particularly, to a silicon nitride sintered body which is homogeneous and has high strength and excellent sinterability. It relates to a manufacturing method.

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

As is well known in the art, a silicon nitride sintered body is liquid phase sintered and densified by the addition of a sintering aid, and the sintering aid is MgO.
Alkaline earth metal oxides such as, oxides of rare earth metals such as Y ₂ O _3, and there are, such as Al ₂ O _3, these sintering aid and the silicon nitride powder were mixed and pulverized, sintered silicon nitride It is used as a starting material for the body.

However, although the oxide-based additive reacts with silicon nitride or a SiO ₂ film existing on the crystal surface of the silicon nitride powder to form a grain boundary phase, even if these raw materials are sufficiently pulverized and mixed,
The additives do not have a microscopically uniform distribution, and the size of this grain boundary phase becomes non-uniform, resulting in the abnormal growth of silicon nitride sintered grains being promoted, resulting in thick grains. The phase was the source of destruction. In addition, the addition of an oxide increases the ionic bondability and reduces the original excellent properties of silicon nitride. Therefore, in order to improve various properties of the sintered book, particularly mechanical properties, it is necessary to use a non-oxide-based sintering aid to further reduce the amount of the additive and to uniformly disperse it.

(Problems to be Solved by the Invention) In order to uniformly disperse the sintering aid as described above, an attempt is generally made to increase the dispersion efficiency by reducing the particle size of the raw material powder to make it ultrafine. However, when molded using such a finely divided raw material powder, the density of the molded body, more specifically the bulk density of the green compact, tends to decrease, and the sinterability And the shrinkage amount increase, the dimensional accuracy deteriorates, and deformation occurs.

Also, as a sintering aid, a non-oxide type, such as nitride ReN (R
e: Group IIIa metal of the periodic table) has a very high reactivity with water, and the reaction from the nitride to the oxide proceeds during handling. It was the current situation that it did not reach.

(Purpose of the invention) As a result of the inventors of the present invention having conducted research on the above problems, by using an alloy fine powder containing a Group IIIa metal of the periodic table in metallic silicon as a raw material powder, excellent stability, Moreover, they have found that a homogeneous sintered body can be obtained.

Therefore, an object of the present invention is to provide a method for manufacturing a silicon nitride sintered body having excellent stability.

Another object of the present invention is to provide a method for producing a homogeneous and high-strength silicon nitride sintered body.

Still another object of the present invention is to provide a method for producing a silicon nitride-based sintered body having excellent sinterability.

(Summary of the Invention) That is, according to the present invention, after forming an alloy fine powder containing a group IIIa metal of the periodic table in metallic silicon, nitriding at 1300 to 1400 ° C. in a nitrogen atmosphere, and further raising the temperature. Further, there is provided a method for producing a silicon nitride-based sintered body, which is characterized by being sintered at a sintering temperature of 1700 ° C. or higher.

(Means for Solving Problems) Hereinafter, the present invention will be described in detail.

According to the present invention, it is extremely important to use, as a raw material composition, an alloy fine powder in which a group IIIa metal of the periodic table (hereinafter simply referred to as a group IIIa metal) is contained in metallic silicon. According to the present invention, by alloying metallic silicon and a Group IIIa metal, the stability to oxygen or water vapor in the atmosphere is improved, and the Group IIIa metal in the metallic silicon is compared with each other. Dispersibility is improved. with this. There is no need to make the raw material ultrafine when molding the raw material composition, and it is possible to reduce the decrease in the bulk density of the green compact as a green compact, and also to homogenize the green compact and further to homogenize the sintered compact. Can also be achieved.

According to the present invention, the above-mentioned raw material fine powder is a well-known molding method,
For example, after being molded by a die press molding method, a casting molding method, an injection molding method, an extrusion molding method, etc., the molding process is transferred to a sintering step.

In the sintering process, the first step is 1300 ~ in a nitrogen atmosphere.
The raw material powder is nitrided at a temperature of 1400 ° C. By this nitriding treatment, the raw material powder is Reaction proceeds. However, when the metal alloy and the nitrogen gas directly react with each other, heat generation is intense, and therefore a technique for suppressing the reaction is required. For example, it is desirable to proceed the nitriding reaction in the presence of hydrogen gas or ammonia gas while controlling the heating rate. The product of the nitriding reaction of equation (1) Si ₃
Since N ₄ -MN has the effect of a sintering aid during sintering, it is possible to promote sinterability when the temperature is further raised.

Next, after the above nitriding reaction is completed, the temperature is further raised and sintering is performed at 1700 ° C. or higher. In this sintering process, Si ₃ N
Sintering proceeds in the _4- MN state. At this time, the MN (M: Group IIIa metal) generated by the nitriding reaction of the formula (1) does not remain at the grain boundary due to the reaction with Si ₃ N _4, and is stabilized because of oxidation and high temperature of the sintered body. Inferior strength is suppressed.

According to the present invention, it is desirable to set the content of the group IIIa metal in the alloy composed of silicon metal and the group IIIa metal in the range of 0.1 to 30% by weight, preferably 0.5 to 10% by weight. That is, if the group IIIa metal is less than 0.1% by weight, it is difficult to expect an effect on the sinterability for achieving the object of the present invention.
Further, it has been found that if the amount exceeds 30% by weight, the alloy itself becomes unstable and the characteristics of the sintered body deteriorate.

Sc, Y, La, Ce, Pr, Nd, Pm, Sm, E which are rare earth elements as Group IIIa metals of the periodic table used in the present invention
One or more selected from u, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu can be mentioned, and among these, Sc, Y, and Pc are particularly preferable.

The alloying of silicon metal and Group IIIa metal of the periodic table can be adopted a usual method, for example, after mixing metal silicon powder and Group IIIa metal, melted at 1400 to 1600 ° C. in a non-oxidizing atmosphere, Obtained by cooling. The lump after cooling is coarsely crushed and then finely crushed, and the average particle size is 0.5 to 10 μm.
It is desirable to set the size to a value that improves the bulk density during molding, reduces the amount of shrinkage, and facilitates the nitriding treatment.

According to the present invention, in addition to the Si-IIIa group metal alloy, Al ₂ O
It is also possible to further add sintering aids such as ₃ , Y ₂ O ₃ and MgO.

The invention is illustrated by the following example.

(Example) Metallic silicon powder and rare earth metal powder were weighed at the compounding ratios shown in Table 1, mixed, and then melted in a temperature range of 1400 to 1600 ° C to obtain an alloy. This alloy was pulverized by a well-known method such as a ball mill to an average particle size of about 2 μm to obtain an alloy fine powder having a composition shown in Table 1.

If desired, other additives were mixed with the obtained fine powder in the proportions shown in Table 1 to obtain a raw material powder.

The raw material powder was sintered in the sintering process shown in Table 1 to obtain a sintered body.

The specific gravity of the obtained sintered body was measured by the Archimedes method.
Four-point bending according to JIS R 6101 (test piece: 4 x 3 x 42 mm)
The bending strength was measured by.

As a result of the measurement, there was little residual Si, and a sintered body having excellent specific gravity and strength was obtained.

(Comparative Example) either silicon nitride fine powder in the _{Y 2 O 3, Al 2 O} 3, YN formulated on the basis of Table 1, the sintering conditions in Table 1, the sintered body No.
4, 5 and 6 were produced and the characteristics were measured in the same manner as in the example.

The results are shown in Table 1.

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

(Effect of the invention) According to the production method of the present invention, by using an alloy powder of silicon metal and a metal of Group IIIa of the periodic table as a raw material powder, chemical stability of the raw material powder can be obtained and sintering can be performed. Since the contributing group IIIa metal itself is uniformly dispersed in the raw material stage, a homogeneous silicon nitride sintered body having high strength and chemical stability can be obtained. Further, the sinterability can be further promoted by the nitride generated by the nitriding reaction of the raw powder in the sintering process.

Claims (2)

[Claims] 1. After molding an alloy fine powder containing a group IIIa metal of the Periodic Table in metallic silicon, it is heated in a nitrogen atmosphere at 1300 to
After the nitriding treatment at 1400 ° C., the temperature is further raised, and the sintering is performed at a sintering temperature of 1700 ° C. or higher. 2. A metal of Group IIIa of the periodic table in the fine alloy powder.
Claim 1 contained in an amount of 0.1 to 30% by weight
Item 6. A method for manufacturing a silicon nitride sintered body according to the item.