JPS60131865A - Manufacture of silicon nitride ceramics - 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] [Technical field of invention] The present invention relates to a method for manufacturing silicon nitride ceramics.

[Technical background of the invention]

Sintered bodies containing silicon nitride as a main component (silicon nitride ceramics) have excellent heat resistance, being able to withstand high temperatures of about 1900°C, and also have a low coefficient of thermal expansion and excellent thermal shock resistance. Attempts are being made to apply these silicon nitride ceramics to structural parts that require high strength at high temperatures, such as diesel engines and gas turbines, as well as corrosion-resistant and wear-resistant parts.

By the way, as for the manufacturing method of silicon nitride ceramics, since silicon nitride is difficult to sinter by itself,
A method of adding auxiliary agents such as rare earth element oxides and magnesia as additives and performing densification sintering such as pressureless sintering, hot pressing, and HIP is employed.

[Problems with background technology]

When silicon nitride ceramics are used as a structural material, a high degree of homogenization is required, especially in terms of strength at room and high temperatures. However, it is extremely difficult to produce highly homogenized silicon nitride ceramics using the conventional methods described above.

[Purpose of the invention]

The present invention aims to provide a method for producing silicon nitride ceramics that have not only high heat resistance and high strength but also uniform strength.

[Summary of the invention]

Through the research described below, the present inventors have developed a method for producing highly homogenized silicon nitride ceramics.

It is known that when an α-silicon nitride (α-81sNa)-rare earth element oxide system is sintered, crystal grains grow into long columnar shapes during the conversion from α to β, resulting in improved strength. However, it is very difficult to control the aspect ratio in the growth of such crystal grains, and since the strength is determined particularly by the crystal grain size in the longitudinal direction, variations inevitably occur.

Based on this, the present inventors calcined a mixture of α-8i3N4 and rare earth element oxides to convert α→β and grow crystal grains in the form of long columns. I crushed it to make the aspect ratio the same. However, it has not been possible to obtain highly homogenized silicon nitride ceramics by simply sintering calcined powders with the same aspect ratio.

Therefore, the present inventors conducted a thorough study on the grain growth of the crushed calcined material and found that the ratio of the cape at the time of calcining has a significant effect, and based on this, the ratio of Φ1 was set to 1 to 0. 1
By re-sintering the pulverized powder, it was found that highly homogeneous silicon nitride ceramics with uniform strength could be obtained.

The manufacturing method of the present invention will be explained in detail below.

First, silicon nitride powder having an alpha content of 80 inches or more, preferably 85 inches or more is prepared. It is desirable to select a silicon nitride powder having an average particle diameter of 2 μm or less, preferably 0.61 to 1 μm.

Subsequently, additives are added to this silicon nitride powder to prepare raw material powder. As the additive, a rare earth element oxide alone or a mixture of a rare earth element oxide and at least one electrode selected from alumina, magnesia, aluminum nitride, iron oxide, titanium oxide, zirconium oxide, and molybdenum carbide is used. The amount of these additives added to the silicon nitride powder is preferably 15% by weight or less, and particularly when the above mixture is used, the amount of rare earth element oxide is preferably 8% by weight or less. Note that the particle size of the additive may be 1 μm or less.

Next, the raw material powder is calcined to have a Φq ratio of 1 to 0.1.
Convert to . The reason for limiting the α ratio due to calcination is that if the ratio exceeds 1, residual α-
The conversion of 8l and N4 to β makes long columnar grain growth less likely to occur and increases the variation in strength. However, if the ratio is less than 0.1, the strength of the obtained silicon nitride ceramics will decrease. The calcination conditions are 1600 to 1850°C, preferably 1700 to 18°C in a nitrogen stream.
It is desirable to set the temperature to 00°C. Temperature during calcination is 16
When the temperature is below 00℃, α-813N4 to β-813N
The conversion to 4 is slow and the grain growth is slow, but 18
When the temperature exceeds 50°C, 513N4 begins to decompose.

Next, the calcined product is pulverized. The particle size at this time is 1 to 5
It is desirable to set it to 0 μm. The reason for this is that if the particle size of the crushed powder is less than 1 μm, the aspect ratio will become smaller and it will be difficult to improve the strength.
If it exceeds this value, defects will become large and strength will tend to deteriorate.

Next, pressureless sintering and hot pressing are performed using the pulverized powder of the calcined product to produce silicon nitride ceramics. It is preferable to carry out this resintering at a temperature of 1700 to 1820°C; below 1700°C, sintering will not proceed sufficiently; on the other hand, if it exceeds 1820°C, 513N4
decomposition begins to occur. Note that when HIP or atmospheric pressure is used for resintering, processing at an even higher temperature is possible.

[Embodiments of the invention]

Next, the present invention will be explained in detail.

Example 1 First, Si3N with an average particle size of 1.0 μm and a 1α content of 92%
4 powder 92% by weight and an average particle size of 0.9 ttm Y2O.

"2o5 powder 3 with 5% powder by weight and average particle size 0.3 μm
A raw material powder was prepared by mixing % by weight. Subsequently, this raw material powder was calcined at a temperature of 1700° C. for 30 minutes in a nitrogen stream. This calcined product had a ratio of 1 to 1 of 0.8. Next, after pulverizing the calcined material to an average particle size of 5.8 μm, the pulverized powder was heated at 1780°C and 300 kFl.
Silicon nitride ceramics were produced by pot pressing for 90 minutes under the condition of /cm2.

The obtained silicon nitride ceramic has a density of 3.24 &
/,,c.

In addition, silicon nitride ceramics was cut into a size of 3X4X36wn, and the three-point bending strength (σ”
), h) was measured, 'B 7 =85k
g/wn2, Wipul coefficient GTI) = 21, and σ1
20, O=”2, 97wn2, m=27, and was found to have extremely high strength and high homogeneity.

Example 2 The same raw material powder as in Example 1 was calcined under different temperature conditions.
The ratio of 1 is 1, 0.6, 0.4', 0.2.

After producing calcined products of 0.1, these calcined products were prepared in Example 1.
Five types of silicon nitride ceramics were manufactured by performing the same treatment as above.

The three-point bending strength of the obtained ceramics was measured, and the results are shown in the table below.

Table Example 7 Raw material powder having the same composition as in Example 1 was calcined to obtain a calcined product with Φ1=0.7, and this calcined product was pulverized to an average particle size of 1.5 μm. Subsequently, after adding 2% by weight of A/N to this pulverized powder, it was molded, and further heated at 1800°C for 20 minutes in a nitrogen atmosphere.
Silicon nitride ceramics were produced by pressureless sintering.

The obtained ceramic has σRT = 78 kg/an
, m=19, which was extremely homogeneous.

〔Effect of the invention〕

As detailed above, according to the present invention, the diesel engine has not only high heat resistance and high strength, but also has uniform strength.
A method for manufacturing silicon nitride ceramics that is effective as a structural material for gas turbines and the like can be provided.

Claims (7)

[Claims] (1) In the production of silicon nitride ceramics consisting of a silicon nitride-additive sintered body, there is a step of mixing additives into silicon nitride with an α content of 80 or more, and calcining this mixture to increase the Φq ratio. a step of converting from 1 to 0.1;
A method for producing silicon nitride ceramics, comprising the steps of pulverizing the calcined material and then resintering it. (2) The method for producing silicon nitride ceramics according to claim 1, wherein the additive is a rare earth element oxide. (3) A patent characterized in that the additive is a mixture of a rare earth element oxide and at least 11[I] selected from alumina, magnesia, aluminum nitride, iron oxide, titanium oxide, zirconium oxide, and molypide/carbide. A method for producing silicon nitride ceramics according to claim 1. (4) The method for producing a silicon nitride ceramic or wax according to claim 1, wherein the calcination is performed in a nitrogen stream at a temperature of 1,600 to 1,800°C. (5) The method for producing silicon nitride ceramics according to claim 1, wherein the calcined material is pulverized to have a grain size of 1 to 20 μm. (6) The method for producing silicon nitride ceramics according to claim 1, wherein the resintering is pressureless sintering. (7) The method for producing silicon nitride ceramics according to claim 1, wherein the resintering is hot-breathing.