JPS6020346B2 - Manufacturing method of high-strength silicon nitride sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high strength and dense silicon nitride aggregates.

Silicon nitride (Si3N4) crystals have excellent thermal shock resistance due to their unique low coefficient of thermal expansion, as well as excellent mechanical strength, hardness, and chemical stability, so they are attracting attention as a variety of high-strength heat-resistant materials. There is.

However, silicon nitride itself has poor durability and has the property of volatilizing and decomposing at around 1900 qo under atmospheric pressure, so various researches have been conducted on competitive bonding methods. Among these methods, the hot pressing method produces a dense sintered body with high strength, but it is difficult to produce products with complex shapes, and the ordinary hot pressing method and the reactive pressing method evaporate into the sintered body in an atmosphere of 1 atm. As a result, there were many pinholes and it was not possible to obtain a material with high strength. However, since the Shintsu sintering method is the simplest firing method, it would have great industrial significance if a silicon nitride composite with sufficient strength could be obtained by this method. In order to meet these demands, the present inventors conducted intensive research and found that by adding Mg0 and Zr02 to Si3N4 in a specific proportion and sintering it in a specific atmosphere, a dense and high-strength bran compact can be produced. They found that it can be obtained and completed the present invention.

In other words, the gist of the present invention is that within the range surrounded by the quadrilateral area connecting points A, B, C, and D of the attached ternary composition diagram (including on the straight line connecting A, B, C, and D) in terms of weight percentage, The proportion of S
i3N4, Mg○ and Zr02, but points A, B, C
and D is Si3N4 MgO Zr0
2A 98.5% 0.5 more 1 Grandchild B
89% 10% 1%0 80 omitted 10* 10% D 80% 0.5 shot A mixed powder consisting of 19-5% is molded, and the molded body is placed in nitrogen or a mixed gas of nitrogen and inert gas. The present invention provides a method for producing a high-strength silicon nitride sintered body, which is characterized by competitive bonding in a pressurized atmosphere of 1.5 to 130 kg/(absolute pressure, hereinafter the same).

The present invention will be explained in detail below. The reason why the pressure of the atmosphere during sintering in the method of the present invention is limited to 1.5 to 130k9/ is that below 1.5k9/, the decomposition and volatilization of silicon nitride is suppressed. The effect is small, and if it is 130x9/2 or more, the air bubbles in the sintered body will be under high pressure, and the driving force of sintering that tries to block the air bubbles will be offset by the capillary phenomenon during bonding, and the equipment will also be large, resulting in poor productivity and high costs. This is because it is expensive.

Furthermore, the reason for sintering in nitrogen or a mixed gas of nitrogen and an inert gas is that silicon nitride is extremely easily oxidized. Bidding is usually from 1,600 to 210,000, preferably from 1,700 to
If the temperature is lower than 1600 qo, the formation may be insufficient, and if the temperature is higher than 2100 qo, the volatilization of Si3N4 will be significant.
The following will be explained in detail with reference to Examples.

Example 1 Weight % of Q-Si3N49 and broad weight % of 3-Sj3N41
Si3N4 powder with an average particle size of 1 French and an average particle size of 2
The final Zr02 powder and the average particle size of 0. Autumn Mg○ powder (all commercially available products) was blended in various proportions shown in Table 1, and ground in a ball mill to give an average particle size of 1 French or less.

Camphor was added as a binder to this powder in an amount of 5% by weight based on the total powder, and 5×10×
Press-formed to 3-inch dimensions and then heated to 600℃ in a nitrogen stream.
After heating to ℃ to dissipate the binder, the molded body is heated in a graphite crucible in N2 or a mixed gas of N2 and Ar at 1.5~
Sintered under a pressure of 130k9/m. Obtained sample a~
Table 1 shows the results of measuring various properties of i. Table 1 *1 Only sample b' was phosphorized in a 1:1 mixed gas of N2 and Ar. Others were phosphorized in an N2 atmosphere.

As is clear from Table 1, samples a to b' of the present invention have extremely fewer pinholes inside the compact than samples b'' to i outside the range, and can significantly increase the transverse rupture strength value. did it.
In the above example, the reason why excellent properties such as heat resistance can be obtained by adding Mg○ and Z2 in a specific ratio as subcomponents to the main component Si3N4 is that Z2
reacts with Si3N4 to generate some ZrN, Si02, etc., and at the same time forms a late fringe promotion phase with added Mg0, improving the grain properties and making it granular, and sintering under normal pressure. This is thought to be due to the more developed fibrous crystal phase forming an interlaced structure compared to the original one.

Additionally, since the atmosphere during sintering is pressurized, the decomposition and volatilization of silicon nitride is suppressed, making it possible to perform arm sintering at a higher temperature than when sintering under 1 atm. It is considered that the volume diffusivity was improved and a sintered body with extremely few pinholes could be obtained. Therefore, the reason why the Si3N4 component is set to 80 to 98.5% by weight in the method of the present invention is that when the Si3N4 component is less than 80% by weight, the transverse rupture strength value decreases, and when it exceeds 98.5% by weight, the This is because it becomes necessary to raise the temperature, and in this case, the amount of volatilization during sintering increases, making it impossible to obtain a dense and high-strength sintered body.

The reason why the Mg0 component was set at 0.5 to 1% by weight was because if it was less than 0.5% by weight, no effect as a silk-sintering accelerator was observed, so 1
This is because if the weight percentage exceeds , the amount of volatilization during freezing increases, and the glass phase as a binder component and the phase that softens at high temperatures increase, reducing the high-temperature strength properties of the compact. The reason why Zr02 was set to 1 to 19.5% by weight was 1
If it is less than 2% by weight, the internal structure of the sintered body will be difficult to become fibrous, and no improvement in strength will be obtained.If it is more than 2% by weight, the internal structure will be fibrous, but the sinterability will deteriorate and the strength will decrease. It's for a reason. Also, Mg0 and Zr0 in Si3N4
When 2 of Mg0:Z is added such that 2 is larger than 1/4 and molded by hot pressing, 2 of Z is not stabilized and therefore breaks due to fatigue when repeated stress is applied. 1.5 ~ 130k9/As for that pressure lie stripe, a part of Z2 becomes zirconium nitride without transformation, and the rest of Z2 is stabilized by Mg0, and the unstabilized Z2 becomes zirconium nitride. Since all of it disappears, it becomes a burnt striped body that is resistant to fatigue. It is known empirically that this unstabilized ZrQ disappears. In addition, since the Zr02 in the sintered body according to the present invention is formed by binding in a pressurized atmosphere of 1.5 to 130k9/s, the zirconium nitride lump that is partly untransformed after sintering becomes stabilized. . Generally, Mg0 has the effect of improving the coagulation properties of Si3N4, and Z2 has the effect of inducing a fibrous structure in the sintered body, but the present invention combines the two to exhibit their synergistic effect. .

This is clear from the results of Example 2 below. Example 2 Sintering was carried out in the same manner as in Example 1 except that 2 powders of Z and Mg0 powder were blended in various proportions to 9% by weight of Si3N4 powder.

The transverse rupture strength of the obtained sample was measured and the results are shown in FIG.
As is clear from Figure 2, the subcomponents are Mg○,
The transverse rupture strength is larger when both Z are mixed than when both are used alone.

The mixing ratio of both is preferably 4/1 to 1/4 by weight, particularly preferably 3/2 to 2/3.
In Examples 1 and 2 above, Mg0,Z2 was used, but as is known, an Mg compound such as an Mg salt or a Zr salt, or a Zr compound, which becomes Mg0,Z2 at a temperature below the calcination temperature, may be used. Of course, the present invention also includes such cases.

As detailed above, in the present invention, Si3N4 is blended with Mg0 and Z2 in a specific ratio and sintered in a pressurized atmosphere, so it is possible to easily produce a sintered body with high strength comparable to the hot press method. It is usually obtained by a sintering method and has great industrial value. Of course, unlike the hot press method, it is possible to freely obtain sintered bodies with complicated shapes.

[Brief explanation of drawings]

FIG. 1 is a ternary composition diagram showing the basic components of the present invention, and FIG. 2 is a graph showing the relationship between the amounts of Mg0 and Z added and the transverse rupture strength. Figure 1 Figure 2

Claims (1)

[Claims] 1. Points A, B, and C in the ternary composition diagram in Figure 1 of the appendix in weight percentage.
and the proportion of S within the range surrounded by the quadrilateral area connecting D
i_3N_4, MgO and ZrO_2, but point A,
B, C and D are Si_3N_4 MgO ZrO_
2 A mixed powder consisting of 98.5% 0.5% 1% B 89% 10% 1% C 80% 10% 10% D 80% 0.5% 19.5% was molded, and the molded body was heated with nitrogen. Or 1.5 to 130 kg/c in a mixed gas of nitrogen and inert gas
A method for producing a high-strength silicon nitride sintered body, which is characterized by sintering in a pressurized atmosphere of m^2. 2. The method for producing a high-strength silicon nitride sintered body according to claim 1, wherein the weight ratio of MgO and ZrO_2 is 1/4 or more.