JPS63112468A - 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] [Objective of the Invention] (Industrial Application Field) The present invention can be used as a material for various structural parts used in a wide range of fields such as automobile machinery, chemical equipment, aerospace equipment, etc. In particular, the present invention relates to a method of manufacturing a silicon nitride sintered body suitable for obtaining a fine ceramic material having a high temperature strength of 90%.

(Conventional technology and its problems) Sintered bodies mainly composed of silicon nitride are chemically stable at room and high temperatures, have high mechanical strength, and are useful for sliding parts such as bearings, turbochargers, etc. However, since silicon nitride is difficult to sinter by itself, it is usually used as Mgo, AltOs-Y! Os
A method is used in which sintering is performed by adding a sintering aid such as.

These sinterings are thought to be due to liquid phase sintering mediated by a liquid phase generated during sintering, and after sintering, the liquid phase remains in the sintered body as a glass phase. On the other hand, the properties of the sintered body, such as creep resistance, high temperature strength, and oxidation resistance, are greatly influenced by the second phase, that is, the glass phase, remaining in the sintered body. Furthermore, the glass phase produced from the above-mentioned sintering aids has a low softening temperature, and therefore deteriorates the high-temperature mechanical properties of the silicon nitride sintered body, making it undesirable.

On the other hand, as a silicon nitride sintered body with excellent high-temperature mechanical properties,
Y to silicon nitride powder! A method is known in which 01 is added and hot-pressed in a nitrogen atmosphere. However, although the Hontopress method produces a dense sintered body with good sinterability, it suffers from the disadvantage that it can only produce products with simple shapes.

This invention was made by paying attention to the above-mentioned conventional problems, and has particularly excellent strength at high temperatures. It is an object of the present invention to provide a method for manufacturing a silicon nitride sintered body that can manufacture products with complex shapes.

[Structure of the invention]

(Means for solving the problem) The method for producing a silicon nitride sintered body according to the present invention includes silicon nitride: 61 to 95 weight i%, one type selected from group U [a group elements of the periodic table excluding Ce] Oxide: 5 to 35 weight S, S
iO,: 4m of silicon nitride! % or less, 7 other oxides: C
5X amount% of oxides of group 1 elements of the periodic table excluding e
A molded body obtained by mixing and molding raw material powders consisting of the following,
1850℃ or more 2200℃ under nitrogen atmosphere of 2 atmospheres or more
It is characterized in that a sintered body with a theoretical density of 93% or more is obtained by firing at the following temperature.

That is, in this invention, the softening temperature of the second phase remaining in the sintered body is raised by using only one type of oxide of an element in group IIIa of the periodic table excluding Ce as a sintering aid in the silicon nitride powder. This problem was solved by focusing on what was possible.

The reason for excluding cerium (Ce) is that Ce Ot reacts with Si and N4 during firing to generate 5iot, which lowers the high temperature strength of the sintered body.

Furthermore, if Sin is 4% by weight more than silicon nitride, the high-temperature strength of the sintered body will be extremely reduced. i
If it is more than 1%, the high temperature strength of the sintered body will be extremely reduced, so the upper limit of the blending ratio of Sin and other oxides is set to be below the above value.

Addition of one type of oxide of Group A element of the periodic table as a sintering aid for ceramics is effective at the conventional firing temperature (160°C).
In the range of 0 to 1800℃), a sufficient amount of low-viscosity liquid phase is not produced and the sintering properties are poor. Just in case.

According to this invention, one type of oxide selected from Group IIIa elements of the periodic table excluding Ce is used as a sintering aid, and temperature
By performing gas pressure sintering at a temperature below °C, a sufficient amount of low-viscosity liquid phase is generated and densification is promoted without applying external pressure, resulting in sintering with a density of 93% or more of the theoretical density. I was able to obtain a body. Moreover, since the second phase of this sintered body has a high melting point, even if it remains in the sintered body after sintering, the strength is unlikely to decrease at high temperatures.

The silicon nitride in the raw material powder used in this invention is preferably an alpha-type powder, but a beta-type or amorphous powder may also be used.

In addition, oxides of elements in group 1na of the periodic table excluding Ce include Sc, Y, La, Pr, Nd, Pm, Sm, E
u.

Gd, Tb, Dy, Ho, Er, Tm, Yb
, and oxides of Lu. Although the optimum range of these oxides varies depending on the type and composition, the density and strength of the layer can be improved by controlling the content to 5 to 35'iL. However, adding the auxiliary agent in an amount greater than that required for densification causes a decrease in strength at high temperatures.

The method for molding these mixed powders is not particularly limited, but for example, any conventional ceramic molding method such as mold press molding, rubber press molding, or injection molding can be selected according to the shape of the desired product.Next, Firing is performed in a nitrogen atmosphere of 2 atmospheres or more. In this case, the nitrogen atmosphere prevents oxidation of silicon nitride and
The purpose is to suppress decomposition, and this effect is small below 2 atmospheres. Note that the atmospheric gas is preferably 100% nitrogen gas, but a mixed gas with other inert gases may also be used. In addition, in order to suppress transpiration due to SiO gas during sintering, Si8N4 + S I O! Although it is not necessarily necessary to sinter the sample with a mixed powder such as, it is an effective method when sintering is performed at high temperatures. Furthermore, regarding the sintering temperature, although the optimum temperature varies depending on the type and amount of raw material powder, it is performed at 1850° C. or higher and 2200° C. or lower.

At temperatures below 1850°C, no liquid phase is generated and densification does not occur. At 2200° C. or higher, silicon nitride grains grow significantly and the strength decreases.

In one embodiment of the present invention, when firing the molded body, ■ 1850° C. at a pressure of 2 atm or more and 500 atm or less;
After performing the primary firing at a temperature of 2200℃ or less, ■
It is characterized in that the secondary firing is performed at a pressure of 500 atm or more and a temperature of 1850°C or more and 2200°C or less. This is densified to 90% or more of the theoretical density in step (2), and the pores of the molded product become closed pores. The increased nitrogen gas pressure in step (2) has the effect of eliminating the pores inside the molded body, and the addition of a small amount of auxiliary agent has the effect of producing a high-density sintered body. The reason for firing at a pressure of 500 atm or less in (2) is that under a gas pressure of 500 atm or more, final sintering will be hindered and complete densification will not occur.

(Implementation ψli l-12) 2.5 wt% of silicon nitride powder with Sin as an impurity
Rare earth oxide (
(purity of 99.9% or more) was mixed with the composition shown in Table 1, and then milled in a wet ball mill with ethanol added using a silicon nitride ball and a plastic pot for 24 hours.

During this period, the amount of wear on the balls was small and impurity contamination from the balls was rarely less than 0.1%. The obtained mixed powder was
Mold molding at a pressure of G9 f/crl followed by 200
Rubber press with 0#f/d pressure to 5+o+X6mg
A friend molded into a plate shape of X50. This was fired by holding it for a predetermined time at the nitrogen gas pressure and temperature shown in Table 1. Next, the surface of this sintered body is ground and
After processing into the shape of 0 mm, a bending test was conducted at 3 points and 1 flll with a span of 30 mm at temperatures of 25°C and 1350°C (Examples 1 to 9) a Theoretical density as shown in Table 1 A dense sintered body with a density of 93% or more was obtained, and had high strength and smoothness at room temperature and little decrease in strength at high temperature. However, the strength at 25°C is the average of 15 specimens, and the strength at 1350°C is the average of 3 specimens.

Powder having the composition shown in Table 2 was fired under the conditions shown in FIG. 1 (other conditions being the same as in the above example). The results are shown in Table 2. (Examples 10 to 12) (Comparative Examples 1 to 7) Powders having the compositions shown in Table 3 were fired under the conditions shown in Table 3.

The results are shown in Table 3.

〔Effect of the invention〕

According to the present invention, a t-silicon nitride sintered body having particularly excellent strength at high temperatures can be manufactured by gas pressure sintering, which enables the manufacture of products with complex shapes.

[Brief explanation of the drawing]

FIG. 1 is a temperature and pressure-time diagram showing the firing conditions of Example to-12 of the present invention.

Claims (1)

[Claims] Silicon nitride: 61-95% by weight, No. 1 of the periodic table excluding Ce
One type of oxide selected from group IIIa elements: 5 to 35% by weight, SiO_2: 4% by weight or less of silicon nitride, other oxides: 5% by weight of oxides of group IIIa elements of the periodic table excluding Ce A molded body obtained by mixing and molding the raw material powders consisting of the following is
A method for producing a silicon nitride sintered body, which obtains a sintered body by firing at a temperature of 200° C. or lower.