JPS63195170A - Manufacture of silicon nitride 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] [Object of the Invention] (Industrial Field of Application) The present invention relates to silicon nitride sintered material used as a material for parts that are required to have excellent heat resistance, corrosion resistance, etc. The present invention relates to a method of manufacturing a silicon nitride sintered body suitable for manufacturing a body.

(Prior art) Sintered bodies whose main component is silicon nitride are chemically stable at room and high temperatures, have excellent heat resistance, and have high mechanical strength, making them suitable for sliding applications such as bearings. It is a suitable material for parts and engine parts such as turbocharger rotors.

Conventional methods for manufacturing silicon nitride sintered bodies include, for example,
Known methods include (2) nitriding a molded body of silicon (Si) powder, and (2) adding an oxide auxiliary agent to silicon nitride (Si3Na) powder and sintering it.

Among these, the silicon nitride sintered body manufactured by the former method Φ has the feature that its strength does not decrease even at high temperatures, and the silicon nitride sintered body manufactured by the method Although they have the feature of excellent strength at room temperature, neither strength nor fracture toughness value (K!c) could be said to be sufficient.

On the other hand, as a method for producing a silicon nitride sintered body with a high fracture toughness value, there is a method in which an oxide aid and whiskers are added to silicon nitride (Si3Na) powder, and then sintered by hot pressing or pressureless sintering. Ta.

However, although the silicon nitride sintered body produced by this method of manufacturing a silicon nitride sintered body has improved fracture toughness (KIC), the improvement in strength is not very large. . This is because the introduction of whiskers inhibits the densification of silicon nitride, resulting in insufficient densification or defects due to insufficient local densification.

(Objective of the Invention) The present invention has been made in view of the above-mentioned conventional problems, and it is possible to obtain a silicon nitride sintered body having excellent strength and fracture toughness. The object of the present invention is to provide a method for producing a solid body.

[Configuration of the Invention (Means for Solving the Problems) The method for producing a silicon nitride sintered body according to the present invention is characterized in that silicon (S
i) After preparing a raw material powder by adding and mixing, for example, ceramic whiskers to the powder, the raw material powder is molded to preferably a density of 55% or more, and the obtained molded body is heated to 100 to 100 mm in a nitrogen atmosphere. By nitriding at a temperature of 1500°C, the theoretical density ratio is more preferably 80%.
The present invention is characterized in that the silicon nitride sintered body described above is obtained.

The present invention provides that the silicon nitride sintered body manufactured according to the present invention has the characteristics of the conventional reaction-sintered silicon nitride sintered body, that is, the strength does not decrease even at high temperatures.
The aim is to improve the low strength and fracture toughness value (KIc), which are disadvantageous.

In this invention, the raw material powder prepared by adding whiskers to a bundle of silicon and raw powder is molded to a density of more preferably 55% or more; This is because if it is low, the density after nitriding will be low and the strength of the sintered body may be reduced.

The molded body is then fired in a nitrogen atmosphere, but the firing atmosphere at this time is not necessarily limited to a 100% nitrogen atmosphere, and may be a mixed gas with other gases. For example, a N2-10% H2 atmosphere may be used, or high pressure nitrogen gas may be used to increase the nitriding rate.

On the other hand, when the firing temperature for causing the nitriding reaction is lower than 1000°C, the reaction is slow, and at a temperature higher than 1500°C, St melts, making it impossible to maintain the shape. Therefore, the firing temperature is 1000-1500℃
It is better to

The whisker-added silicon nitride sintered body manufactured according to the present invention has a high density of 80% or more of the theoretical density ratio, has whiskers evenly dispersed, and has a higher density than a silicon nitride sintered body without whiskers. It exhibits high values for both strength and fracture toughness (Kxc), and also has the feature that the strength does not decrease even at high temperatures, which is a feature of reaction-sintered silicon nitride sintered bodies.

The method for producing a silicon nitride sintered body according to the present invention includes silicon (S)
t) In addition to adding and mixing, for example, ceramic whiskers to the powder, whiskers of group 1Ia of the periodic table.

After preparing a raw material powder etc. by adding and mixing an oxide of at least one element selected from the group consisting of Group 111a, Zr and Ai, the raw material powder etc. is molded, and the obtained molded body is placed in a nitrogen atmosphere. treated at a temperature of 1000 to 1500 °C under
It is also preferable to obtain a silicon nitride sintered body having a theoretical density ratio of 80% or more by processing at a temperature of 2200°C.

Even in this case, the silicon nitride sintered body manufactured according to the above manufacturing method has the advantage of the conventional reaction-sintered silicon nitride sintered body, that is, the strength does not decrease even at high temperatures, Some low strength and fracture toughness values (
The aim is to improve the KIC).

After the raw material powder prepared above is molded into a predetermined shape,
This molded body is fired in a nitrogen atmosphere, but the firing atmosphere at this time is not necessarily limited to a 100% nitrogen atmosphere, and may be a mixed gas with other gases, such as N2-10 %H2 atmosphere may be used, and
High pressure nitrogen gas may be used to increase the nitriding rate.

On the other hand, when the firing temperature for causing the nitriding reaction is lower than 100°C, the reaction is slow, and at a temperature higher than 1500°C, St melts and the shape cannot be maintained. The temperature is preferably 1500°C.

Next, it is preferable that the fired body is treated at a temperature of 1600°C to 2200°C in a nitrogen atmosphere of 1 atm or more, and in this case, firing at 1600°C to 2200°C:
It can also be carried out using hot press, HIP (hot isostatic pressing), or the like.

1600~22 under such a nitrogen atmosphere of 1 atm or more
By performing the firing at 00°C, a liquid phase of the oxide of the above-selected element is generated, and the pores remaining inside the sintered body are eliminated by pressurization, thereby further densifying the sintered body. It becomes possible to increase the strength by increasing the density. However, when the temperature is lower than 1600°C, a sufficient liquid phase of the oxide cannot be obtained, and when the temperature is higher than 2200°C, the grain growth of silicon nitride increases, resulting in a decrease in the strength of the 160°C.
It is preferable to perform the densification treatment at a temperature in the range of 0 to 2200°C.

According to the method of the present invention, conventional silicon nitride (S13NA)
Compared to the method using the starting material, the amount of shrinkage is smaller, so the denseness is not inhibited even if it contains a large amount of whiskers.
Fewer defects occur, which improves both strength and fracture toughness (Kxc).

Examples of the whiskers used in the present invention include SiC whiskers, 5L3N4 whiskers, and A-203 whiskers. Not limited,
The size of the whisker used in this case is particularly suitable for whiskers having a diameter of about 0.2 to 100 gm and an aspect ratio of 10 or more. That is, the diameter is 0.2
If the diameter is smaller than 100 gm, the strength-improving effect tends to be less. On the other hand, if the diameter is larger than 100 gm, the whisker introduction part is likely to become a defect, which may reduce the strength. Also, the aspect ratio is 1
When it is less than 0, the effect on improving strength tends to be small. On the other hand, the amount of whiskers added is more preferably about 10 to 30% by volume in terms of the amount of whiskers in the final sintered body. The reason for this is that if the amount is less than 10% by volume, the effect of addition will be reduced, and if it is more than 30% by volume, densification may become difficult.

(Example) Examples of the present invention will be described below along with comparative examples.

<Example 1> Silicon (St) powder with an average particle size of 10 gm and a purity of 99.9% and silicon carbide (S i C) whiskers with an average diameter of 0.6 pm and an average length of 20 gm were combined into a nitriding reaction product with a weight of 10 gm and a purity of 99.9%. Blend so that the ratio becomes the composition shown in Table 1, and 2
A raw material powder was prepared by mixing in a ball mill for 4 hours.

Next, the above raw material powder was made into a size of 6 x 6 x 50 mm by 200 mm.
It was molded at a pressure of Kgf/cm2.

The density of the compact obtained here after compaction was 48 of the theoretical density.
The molded body was then coated with a rubber coating, and then rubber pressed at a pressure of 100100 O0/cm'.

The density of the green compact obtained here after rubber pressing was 57 to 60% of the theoretical density.

Subsequently, when the green compact was subjected to nitriding treatment under the conditions of the treatment schedule shown in Figure 1, as shown in Table 1, the density of the sintered compact after nitriding was 80% or more of the theoretical density. A silicon nitride sintered body made of a SiC whisker silicon nitride composite material was obtained.

Next, when each of the sintered bodies obtained as described above was cut and observed, it was found that no unreacted portion was present inside the body. In addition, bending test pieces with dimensions of 3 x 4 x 40 mm were cut out from each sintered body and subjected to a 4-point bending test with a span of 30 mm, and the results shown in Table 1 were also obtained. Table 1 shows the average values measured for 10 test pieces. Furthermore, from each sintered body, 3X4X
An impact test piece with a size of 40 mm and a chevron notch formed in the center was prepared, and the fracture toughness value (K x c) was measured by three-point bending, and the results shown in Table 1 were also obtained.

As is clear from the results shown in Table 1, it was confirmed that a silicon nitride sintered body with high strength and high fracture toughness value (K x c) was obtained.

<Example 2> Silicon (Si) powder with a particle size of 10 pm and a purity of 99.9%, y2o31 N d2 o3j MgO, Au203
, Sm203, and Zr02, and silicon carbide (S i C) whiskers having an average diameter of 0.6 pm and an average length of 20 ILm, the weight ratio after the nitriding reaction is 2nd. The ingredients were blended to have the composition shown in the table and mixed in ethanol using a ball mill for 24 hours to prepare raw material powder.

Next, the above raw material powder was heated to 200K to the dimensions of 8X6X50mm.
After molding with a mold at a pressure of gf/am', the molded body was then coated with rubber, and then heated at a pressure of 2000 kgf/c.
Rubber pressing was carried out at a pressure of m2. Subsequently, the rubber-pressed green compact was subjected to nitriding and densification according to the treatment schedule ① shown in Figure 2. As shown in Table 2, the density of the sintered compact after nitriding was A silicon nitride sintered body made of a high-density SiC whisker silicon nitride composite material having a density of 96% or more of the theoretical density was obtained.

Next, when each of the sintered bodies obtained as described above was cut and observed, there was no unreacted portion inside. In addition, bending test pieces with dimensions of 3 x 4 x 40 mm were cut out from each sintered body, and a 4-point bending test with a span of 30 mm was performed, and the results shown in Table 2 were (!I). The average value measured for the book test piece is shown.Furthermore, 3X
An impact test piece with dimensions of 4 x 40 mm and a chevron notch formed in the center was prepared, and the fracture toughness value (K2c) was measured by three-point bending, and the results shown in Table 2 were also obtained.

As is clear from the results shown in Table 2, it was confirmed that a silicon nitride sintered body with even higher strength and higher fracture toughness (KIC) could be obtained.

Comparative Example 1 In this comparative example, a silicon nitride sintered body was produced using the same process as in Examples 1 and 2, except that SiC whiskers were not added to the silicon (Si) powder. . As in Examples 1 and 2, the density 2 bending strength and fracture toughness value (Ktc
), the results shown in Table 3 were obtained.

As is clear from the results shown in Table 3, the comparative silicon nitride sintered body (No. 8) corresponding to Example 1 and the comparative silicon nitride sintered body (No. 9) corresponding to Example 2
, 10), the bending strength and fracture toughness values (K
xc) was found to be a considerably low value.

Comparative Example 2> An oxide consisting of Y2O3 and Nd2O3 and silicon carbide (S i C) whiskers were added to α-silicon nitride (Si:yN4) powder with an average particle size of 1.4 pm.
:Y203 :Nd203 :SiC whisker=68:
They were added in a ratio of 6:6:20 (wt%) and mixed using a ball mill, and the resulting mixed powder was 6×6
It was molded into a size of x50 mm with a pressure of 200 kgf/cm2.

Next, the obtained molded body was rubber-coated, and then rubber-pressed at a pressure of 2000 kf g/cm2c7). Next, the pressed powder compact was fired using a rubber press under the conditions of the treatment schedule (3) shown in FIG. 3 to produce a silicon nitride sintered body.

The density of the silicon nitride sintered body produced in this way is
It is 93.0% of the theoretical density, which is low, and the bending strength is 45.
3kgf/cm”, fracture toughness value (Kyc) is 6.2
MPaFi was also a low value.

[Effects of the Invention] As explained above, the method for producing a silicon nitride sintered body according to the first aspect of the present invention includes adding whiskers to silicon powder to prepare a raw material powder, and then adding the raw material powder to the silicon nitride sintered body. mold,
The obtained molded body was heated at 1000 to 1500°C under a nitrogen atmosphere.
A sintered body is obtained by processing at a temperature of
In addition, it is preferable that the silicon powder contains Group 1Ia, Group 1 of the Oka period table.
Group 1a.

After preparing a raw material powder by adding and mixing an oxide of at least one element selected from the group consisting of Zr and Al and whiskers, the raw material powder is formed.

The obtained molded body was heated to 1000 to 15
Since the sintered body is obtained by processing at a temperature of 1,000°C and then preferably at a temperature of 1,600 to 22,000°C under a nitrogen atmosphere of 1 atm or more, both strength and fracture toughness are significantly improved. It is possible to produce a silicon nitride-based sintered body that exhibits excellent values, and it is also possible to obtain a silicon nitride-based sintered body that has excellent properties that do not easily lose strength even at high temperatures. is brought about.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the treatment schedule adopted for the nitriding treatment of the green compact in Example 1 of the present invention, and FIG. 2 is a graph showing the nitriding treatment and densification treatment of the green compact in Example 2 of the present invention. A graph showing the processing schedule adopted for
FIG. 3 is a graph showing the treatment schedule ring adopted for the firing treatment of the green compact in Comparative Example 2.

Claims (1)

[Claims] (1) After preparing a raw material powder by adding and mixing whiskers to silicon powder, the raw material powder is molded, and the resulting molded body is treated at a temperature of 1000 to 1500°C in a nitrogen atmosphere to form a sintered body. A method for producing a silicon nitride sintered body, characterized in that: