JPS62119165A - Silicon nitride base 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 [Industrial Application Field] The present invention relates to a silicon nitride sintered body, and particularly to a high-density silicon nitride sintered body that has excellent mechanical strength at room temperature and little decrease in strength at high temperatures.

C. Conventional technology] Silicon nitride sintered bodies have mechanical strength, heat resistance, and corrosion resistance.

Due to its excellent thermal shock resistance, it has recently attracted attention as a material for high-temperature structural materials such as gas turbine parts. However, since silicon nitride has a high covalent bonding property, it has poor sinterability, and it is difficult to obtain a high-density and high-strength sintered body from silicon nitride alone. Therefore, when sintering silicon nitride, attempts have been made to add and distribute MgO, AQ203, rare earth element oxides, etc. as sintering aids. The role of these sintering aids is to react with a trace amount of 5ioz present on the surface of the silicon nitride raw material, generate a low melting point glass phase, and promote sintering. Therefore, the final sintered body obtained using these sintering aids has a β'-silicon nitride composition (Sie-zA Q z
Oztls-z O<Z<4, 2) and a grain boundary phase. However, this grain boundary phase is generally
Since it is a glass phase that softens from around 1000°C, it has been the main cause of deterioration of the high temperature strength of the sintered body.

In order to solve this problem,
To do this, AQzG8 or AQN and rare earth element oxides are added to silicon nitride to form a grain boundary phase of 5isN4/R2.
08 (R represents an element in group 1 Va of the periodic table) type crystal structure, and a method for producing a high-temperature, high-strength material is described. However, with this method, the three-point bending strength was not very high at room temperature, about 120 kg/nw", and the strength at 1200° C. was also about 110 kg/tm".

[Problem that the invention seeks to solve]

In the above conventional technology, in order to precipitate 5iNa.R2O3 in the grain boundary phase, it is necessary to make the amount of oxygen in the grain boundary phase relatively small. For this reason, a sintering aid containing oxygen element, namely Aug.
The amount of Os is limited and is about 2% by weight. Therefore, the amount of grain boundary phases produced during the sintering process is reduced, and this small amount of produced grain boundary phases is the reason why room temperature strength cannot be increased.

That is, in the sintering of silicon nitride, α-5iN+
There is a process in which α-3iaN4 particles are dissolved in the liquid phase generated around the raw material powder particles and precipitated again as β-3isNi crystals. At this time, the β-3iaNi crystal grows into anisotropic particles (columnar/acicular shape), and the entanglement of these particles makes it possible to increase the strength of the silicon nitride sintered body. Therefore, the larger the amount of liquid phase produced, the easier it is to form anisotropic particles, and the degree of entanglement becomes greater. Therefore, the larger the amount of liquid phase, the higher the strength can be achieved.

In the conventional technology in which 5isN+・RzOs is precipitated in the grain boundary phase, the amount of liquid phase generated in the sintering process is small, so the acicular β
'-3isNa particles are not sufficiently developed and the room temperature strength becomes small.

An object of the present invention is to provide a silicon nitride sintered body that has excellent strength at room temperature and less decreases in strength at high temperatures.

[Means for solving problems]

Regarding silicon nitride sintered bodies with little strength loss at high temperatures,
In order to solve the conventional drawback of low strength at room temperature, we added an auxiliary agent to the composition powder that produces a large amount of liquid phase and has high room temperature strength, and various studies were conducted. The inventors have discovered that this sintered body exhibits no strength deterioration even at high temperatures and is extremely excellent as a heat-resistant, high-temperature member, leading to the present invention.

That is, the present invention provides a silicon nitride sintered body containing β' 5iaNa as the main constituent phase, in which YzoA Q is present at the grain boundaries.
The present invention relates to a silicon nitride sintered body characterized in that zsj30sδN4 is precipitated.

In the present invention, in order to achieve a composition that generates a large amount of liquid phase and has high room temperature strength, aluminum nitride, aluminum oxide, and yttrium oxide are added to silicon nitride, and an oxide of a rare earth element, such as erbium oxide, is added. This is an essential condition. By adding an appropriate amount of auxiliary agent to such a silicon nitride composition with high room temperature strength, YLOA Q zsi^01MN4 crystals are precipitated in the grain boundary phase, resulting in not only high room temperature bending strength but also high temperature resistance. This results in a sintered body that has far superior mechanical strength to conventional products.

In order to obtain the silicon nitride sintered body of the present invention, for example, it contains 80 to 95% by weight of silicon nitride, 3 to 10% by weight of yttrium oxide, 4 to 10% by weight of aluminum oxide, and 0.1 to 3% by weight of aluminum nitride. What is necessary is just to mix|blend so that 3-20 mol% of rare earth oxides may be contained with respect to the silicon nitride composition powder formed by.

The reason why the powder composition is limited to the above composition range is as follows.

Silicon nitride: 80 to 95% by weight If the silicon nitride content is less than 80% by weight, the amount of grain boundary phase increases, resulting in poor high-temperature properties. On the other hand, if it exceeds 95% by weight, the amount of the sintering aid decreases and the sinterability deteriorates, so the silicon nitride content was set in the range of 80 to 95% by weight.

If the amount of at least one of yttrium oxide 11, aluminum oxide, aluminum nitride, and 21RLQN polytype, yttrium oxide, aluminum oxide, and aluminum nitride 11 is less than a predetermined range, sintering properties will be poor, resulting in high strength sintering. It's impossible to get a body! When B is exceeded, the sinterability improves, but the amount of grain boundary phase increases and the strength decreases significantly at high temperatures. Also, when using 21RA Q N polytype instead of aluminum nitride,
It is necessary that the content is in the range of 1.0 to 5.0% by weight.

If it exceeds this range, sinterability will be inhibited and the strength will decrease.

On the other hand, it is desirable that the amount of rare earth oxides, such as erbium oxide, holmium oxide, thulium oxide, and ytterbium oxide, be 3 to 20 mol % with respect to the silicon nitride composition powder obtained by mixing silicon nitride with a sintering aid as described above. If it is less than 3 mol%, the degree of crystallization of the grain boundary glass phase will be low and will not contribute to high temperature strength.On the other hand, if it is more than 20 mol%, the grain boundary phase will be crystallized, but the grain boundary glass phase will be crystallized. This is because a material with high room temperature strength cannot be obtained due to the large phase ratio.

[Effect]

In the present invention, '11oA A zsjaoxaN4 crystals are precipitated in the grain boundary phase by adding an appropriate amount of rare earth oxide to a composition that produces a large amount of liquid phase and has high room temperature strength,
This makes it possible to produce a sintered body that has not only room temperature strength but also mechanical strength far superior to conventional products even at high temperatures. The reasons for this are: (1) the composition produces a large amount of liquid phase during crystallization, so the β'-3iaNa crystals develop sufficiently into needle shapes, increasing the room temperature strength; (2) the grain boundary glass phase crystallizes, and the Y
This is because zoA Q xsis01sN precipitates at the grain boundaries, resulting in two effects: strength decrease is small even at high temperatures. Therefore, the room temperature strength is 140k.
It is possible to easily obtain a strength of about 100 g/mm, and
The high temperature strength at 1200"C is also about 120 kg/me".

In order to produce the silicon nitride sintered body of the present invention as described above, 80 to 95% by weight of silicon nitride and 3 to 10% by weight of yttrium oxide are added.
After mixing and pulverizing 3 to 20 mol% of a rare earth oxide to a silicon nitride composition powder containing 4 to 10% by weight of aluminum oxide and 1 to 3% by weight of aluminum nitride ls0, forming a molded body, followed by 16
Sintering is carried out in a non-oxidizing atmosphere at a temperature of 00-1900°C. In this production, a ball mill or the like may be used to mix and grind the silicon nitride composition powder and the rare earth oxide, and the pressure during pressure molding is preferably about 1 ton/cd. Normal pressure sintering or pressure sintering is performed in a temperature range of 1950°C. If the sintering temperature is lower than 1,600°C, a sufficiently densified sintered body cannot be obtained, and if it exceeds 1,950°C, silicon nitride itself decomposes rapidly, making it impossible to obtain a healthy sintered body.

In addition, in order to precipitate the YIOA Q 2si30x8N+ crystal phase in the grain boundary phase, the sintering time is required to be 30 minutes or more.
Approximately 2 hours is desirable. Furthermore, the cooling rate after sintering should be as slow as possible in order to maintain thermal phase equilibrium;
A rate of 0° C./min or less is good.

In the above manner, YIOA Q zsisO is added to the grain boundary phase.
A silicon nitride sintered body in which tδN4 crystals are precipitated not only has extremely high nitriding strength but also exhibits little decrease in strength even at high temperatures, making it an optimal material for high-temperature structural members. .

〔Example〕

The present invention will be explained in detail below.

Example 1 86.01% by weight of silicon nitride powder with an average particle size of 0.6 μm and 7.0% by weight of aluminum oxide powder with an average particle size of 1 μm,
After mixing 1.0% by weight of aluminum nitride with an average particle size of 3 μm and 6.0% by weight of yttrium oxide powder with an average particle size of 3 μm with varying amounts of erbium oxide from 1 to 25 mol%, 1000 kg /ad pressure,
Next, this molded body was hot press sintered at 1750° C. in a nitrogen atmosphere of 1 atmosphere for 2 hours by applying a pressure of 300 kg/d. The cooling rate after sintering is 20 °C/mj, n
And so.

After cutting out a 3x4x30+m test piece from this sintered body and polishing the surface, a 3-point bend test was conducted under the conditions of a span of 30 mm and a Flossherad speed of 0, 5 nu/m, i, and n. The strength was measured.

The results are shown in Table 1. According to this table, if the composition is appropriate, the room temperature strength is very high at approximately 150 kg/m2, and when 3 mol% or more of ErzOs is added, the 1200°C strength increases rapidly, reaching 120 kg/mm2. ”
It can be seen that the size increases to a certain extent. However, 20
It can be seen that if the addition amount exceeds mol %, both room temperature strength and high temperature strength decrease.

Figure 1 shows 1 mol% and 15 mol% [! Showing the X-ray diffraction patterns of rzOs additive materials (sample number 5 and sample number 3),
1 mol%, F! For rz9g additive material, β'-3iaN
In contrast, in the case of the 15 mol % Er2O3 additive material, there are many diffraction lines of YroA Q xsj30s8th crystals. This shows that the improvement in high temperature strength is due to the precipitation of YIOA Q 2s'r30xsN+ crystals.

This effect is caused by Ho2O3, TIIIZOII, Yb
A similar result was obtained by adding zOs.

Example 2 As in Example 1, silicon nitride, aluminum oxide, yttrium oxide, erbium oxide powder and 21RiN polytype powder having an average particle size of 3 μm were combined in the proportions shown in Table 2.

This is Example 1. After hot press sintering in the same manner as above, the bending strength at room temperature and 1200°C was measured. The results are shown in Table 2. It can be seen that when 3 to 20 mol % of ErzOs is added, high strength is obtained both at room temperature and at 1200°C.

On the other hand, it can be seen that samples Nos. 11 to 14, which are outside the predetermined composition range of the present invention, are inferior to the products of the present invention in strength at room temperature or 1200°C. These effects are )102011. T
Similar results were obtained with mzO3 and Yb20s additives.

In addition, although the case of hot press sintering was described in the examples, the product of the present invention can be easily obtained not only by this method but also by normal pressure sintering, atmosphere pressure sintering, FT IP sintering, etc. I can do it.

A new technology is under development that uses a slurry of coal and water (cwM) as a fuel for thermal power generation. FIG. 2 shows a burner nozzle tip section that atomizes this fuel slurry. This part requires the following characteristics:

■ Must be resistant to thermal shock during ignition or fuel cutoff. (The higher the strength at room temperature and high temperature, the better) ■ A pressure medium is used to inject the fuel, but it must have creep resistance against this pressure.

■ Must have abrasion resistance against coal.

■ Must be oxidation resistant.

No conventional metal material satisfies the above characteristics.
The use of ceramics for the nozzle tip is being considered. The silicon nitride-based sintered body of the present invention has high room temperature and high temperature strength,
Since it also satisfies other characteristics, it is suitable as a CWM burner chip.

〔Effect of the invention〕

As described above, according to the present invention, a silicon nitride sintered body having excellent room temperature and high temperature strength can be obtained, so that highly reliable high temperature structural materials such as gas turbine parts can be easily manufactured.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an X-ray diffraction pattern of a sintered material added with ErzOs, and FIG. 2 is a schematic diagram of a burner nozzle chip of a boiler for thermal power generation. 1...Fuel supply path, 2...Pressure supply path, 3...Ejection port.

Claims (1)

[Claims] 1. β'-silicon nitride (Si_6_-_zAl_zO_z
In a silicon nitride-based sintered body mainly composed of silicon nitride, which is composed of N_8_-_z, 0<Z<4.2) and grain boundaries, Y_1_0Al_2Si_3O_1 is present at the grain boundaries.
_3N_4(5Y_2O_3・Si_3N_4・Al_
2O_3) A silicon nitride-based sintered body characterized by the presence of crystals. 2. Silicon nitride 80~95% by weight, yttrium oxide 3~
10% by weight of aluminum oxide, 4-10% by weight of aluminum nitride, and 0.1-3% by weight of aluminum nitride, and sintered with 3-20% of rare earth oxide added. A silicon nitride-based sintered body according to claim 1. 3. In claim 2, the rare earth oxide is
A silicon nitride-based sintered body comprising at least one of forminium oxide, erbium oxide, thulium oxide, and ytterbium oxide. 4. A silicon nitride-based sintered body according to claim 2, characterized in that it contains 1.0 to 5.0% by weight of 21RAIN polytype instead of aluminum nitride.