JPS5851910B2 - Titsukakeisokeishyouketsutainoseizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in a sintered silicon nitride yarn and a method for manufacturing the same.

Silicon nitride yarn sintered bodies containing 813N4 as a main component have excellent high-temperature strength, thermal shock resistance, corrosion resistance, etc., and are therefore attracting a lot of interest as heat-resistant structural materials, such as members for high-temperature gas turbines.

These silicon nitride yarn sintered bodies are manufactured by a reactive sintering method that utilizes the nitriding reaction of silicon (Si) or a hot press method in which silicon nitride yarn raw material powder is sintered under pressure.

In particular, the hot press method can be said to be suitable for producing high-strength sintered bodies since it is generally easy to obtain a dense sintered body.

In addition, when obtaining a silicon nitride yarn sintered body by this hot pressing method, for example, magnesium oxide (MgO), aluminum oxide (Al□03), yttrium oxide (Y2
Attempts have also been made to improve sinterability by adding and blending materials such as os) to raw material silicon nitride powder to produce high-strength sintered bodies.

In the above, if rare earth element oxides such as yttrium oxide (Y2O2) are used in combination with aluminum oxide (Al□03), it becomes easier to obtain a silicon nitride yarn sintered body with even higher strength.
For example, when used in turbine blades of high-temperature gas turbines, even higher performance and reliability are required.

As a result of examining the relationship between raw material components, high-temperature strength, and reliability of silicon nitride yarn sintered bodies, the present inventors found that the type, purity, and oxygen content of the silicon nitride powder rice raw materials have a large influence. I found it.

In other words, the α-type crystal system is preferable for the raw material silicon nitride powder, and the particle size is also an important factor, but the amount of oxygen contained in the raw material silicon nitride powder is determined by the final sintered body. It was confirmed that this is a major factor in strength and reliability.

Based on such knowledge, the present invention aims to provide a silicon nitride yarn sintered body that has excellent high-temperature strength and high reliability and is suitable for the construction of high-temperature gas turbine blades, and a method for manufacturing the same.

The present invention will be described in detail below. The present invention includes (a) α
type silicon nitride occupies more than 800 parts by weight and the oxygen content is 2
．． 99. Silicon nitride powder method in which the weight range is 0 to 5.5 and the content of metals other than silicon is 1 weight group or less as metals.
8 to 70 overlapping parts, (b) 0.1 to 10 parts by weight of oxide powder of Ia group elements of the periodic table, and (C) 11 to 20 parts by weight of aluminum oxide powder O, and the above silicon nitride thread sintered body. Mixture of composition 30
0-650 under pressure of 9/cIIt, 1700-183
This is a method for producing a silicon nitride thread sintered body by pressure sintering at 0°C.

As described above, the present invention is characterized in that particular consideration is given to the type and oxygen content of the silicon nitride yarn raw material powder.

To elaborate further on this point, silicon nitride (Si3
N4) powder is generally calcium oxide (CaO) or iron oxide (
t'e2os).

However, if these impurities such as metal oxides other than silicon (Si) are contained as metal in an amount exceeding a single layer, the performance of the obtained sintered body at high temperatures will likely deteriorate, so the amount of impurities should be within the above range. It is necessary to always choose one that is within (preferably 0.4 weight higher yield).

Further, the silicon nitride raw material powder must contain at least 800 parts by weight of α-type crystals.

The reason for this is that if the ratio of α-type silicon nitride to the raw material silicon nitride powder rice is less than 80% by weight, the sinterability will be poor and it will be difficult to finally obtain a high-strength sintered body.

On the other hand, the α-type silicon nitride, which is the main component of silicon nitride powder, has a different oxygen content even though it is the same α-type, and the sinterability is considerably affected by this oxygen content.

The above amount of oxygen is controlled by the amount of other metal oxides contained as impurities, but is always selected within the range of 2.0 to 5.5% by weight.

The reason for this is that if the amount of oxygen contained in the silicon nitride raw material powder is outside the above range, the strength of the obtained sintered body will decrease. In the case of an overlapping part, it is suitable for obtaining a sintered body with even higher performance.

In the present invention, an oxide (second component) of an element in group 1a of the periodic table, which serves as a starting material together with the silicon nitride powder containing α-type silicon nitride as a main component and contributes to improving sinterability and strength, such as Yttrium oxide (Y2O2), lanthanum oxide (La2os), cerium oxide (CeO2) dysprosium oxide (DY203), gadolinium oxide (・Gd
203), samarium oxide (Sm203), etc. may be used alone or in a mixed system of two or more types, and the composition ratio of aluminum oxide (Al2O2)...third component...etc. is 0.1 to 0.1, respectively. 10 weight rice cakes, and 1 to 20 weight rice cakes are selected within the rice cake section.

That is, if the composition ratio of yttrium oxide (Y2O2) etc. as the second component is less than 0.1 parts by weight, it has no effect on sintering properties, and if it exceeds 100 parts by weight, heat resistance at high temperatures, corrosion resistance, etc. decrease. .

Also, aluminum oxide (A1203) as a third component
If the composition ratio is less than 0.1% by weight, yttrium oxide (Y
This is because, like yttrium oxide (Y2 os ), if it exceeds 200 parts by weight, it does not effectively affect the densification of yttrium oxide (Y2 os ), and the high-temperature properties deteriorate.

Therefore, each of these raw material powders preferably has an average particle size of 3μ or less, preferably 0.1 to 2μ, and as a sintering method, pressureless sintering or hot press method can be used, and especially high When the objective is strength, hot pressing is preferred.

The pressure in this hot press is 300 to 650 kg/
cIl, and the sintering temperature is 1700-1830℃
need to be selected.

The reason for this is that selecting the pressure and sintering temperature as described above does not ultimately result in a silicon nitride yarn sintered body having the required performance.

Next, examples of the present invention will be described.

Example 1 α-type silicon nitride accounts for 888 parts by weight, oxygen content is 3.5
Overlapping part (as measured by neutron activation analysis, the same applies hereinafter), 92 parts by weight of silicon nitride powder with an average particle size of 1.0μ, containing 0.6 parts by weight of calcium and iron as impurities, and 92 parts by weight of silicon nitride powder with an average particle size of 1.0μ.
5 parts by weight of stearic acid (binder) was added to a mixed powder consisting of 4.5 parts by weight of 5μ yttrium oxide powder and 2.5 parts by weight of aluminum oxide powder with an average particle size of 0.8μ. A cylindrical body with a diameter of 20 tttm was cold-open molded (pressure: 200 kg/cyrt).

Next, this molded body was preheated to 400°C, the binder was removed, and then placed in a hot press carbon mold, the temperature was gradually raised until the final temperature was 1770°C and 500kg/c.
I! A sintered body was obtained by hot pressing for 2.5 hours.

The width of the sintered body thus obtained is 3ill! fi, thickness 3y
x*1 After cutting out a rod-shaped body with a length of 301 m and polishing the surface, the bending strength (kg/c/L) was measured at a temperature range of room temperature to 1200°C under the conditions of span 20 and load application acceleration of 0.5 ii/min. The results were as shown in Table 1.

For comparison, Table 1 also shows the case of a silicon nitride yarn sintered body obtained under the same conditions except that the silicon nitride powder rice raw material had an oxygen content of 0.855 parts by weight.

As is clear from Table 1, the sintered body according to the present invention has significantly better bending strength than the comparative example.

Example 2 Rice grains with an average grain size of 0.5 parts by weight contain calcium and iron as impurities, and have an oxygen content of 1.4 to 6.5 parts by weight.
A mixed powder consisting of 90 parts by weight of α-type silicon nitride powder of 8 to 1.5μ, 5 parts by weight of yttrium oxide powder with an average particle size of 1.2μ, and 5 parts by weight of aluminum oxide powder with an average particle size of 0.3μ is used as a raw material. Hot pressing was performed under the same conditions as in Example 1 to obtain six types of silicon nitride yarn sintered bodies, including a comparative example.

The measurement results of the density (g/cc) and bending strength at 1200°C (kg/cIIL) of the sintered body thus obtained are shown in Table 2 together with the sintering conditions.

A green compact made from a mixed powder having the same composition as the sample C mentioned above was heated at 1780°C and under a pressure of 500k using a powder vehicle hot press method (using boron nitride powder as the medium).
A sintered body was obtained under the conditions of g/cr/l and 2 hours.

The sintered body thus obtained has a bending strength of 113 kg/f at room temperature.
fl It showed excellent properties with a bending strength of 104 kg/d at 1200°C.

As a comparative example, silicon nitride, which is the same as Sample A of Example 2 and contains 1.2 parts by weight of metal impurities (iron is the main impurity, 0.7 parts by weight, others include Ca, etc.), was used. It is shown in Table-3.

(However, other conditions are the same) Example 3 Silicon nitride with an average particle size of 1μ, containing 888 parts by weight of α-type silicon nitride, 3.5 parts by weight of oxygen, and 0.6 parts by weight of calcium as impurities. Base powder 91 parts by weight, average particle size 1
．． 5 parts by weight of 2μ yttrium oxide powder, average particle size 0.
Silicon nitride fibers were sintered by the hot press method using the same method and conditions as in Example 1, using a mixed powder of 2.5 parts by weight of aluminum oxide powder of 8 μm and 1.5 parts by weight of magnesium oxide with an average particle size of 0.9 μm as raw materials. Obtained a body.

When the bending strength of the sintered body thus obtained was measured, it was 115 kg/crI at room temperature and 92 kg/- at 1200°C.
It showed an excellent value.

As is clear from the above Examples and Comparative Examples, the silicon nitride yarn sintered body according to the present invention has extremely excellent mechanical properties such as bending strength.

Therefore, it can be said that it can be used with high reliability, for example, as a high-temperature gas turbine blade.

Claims (1)

[Scope of Claims] 1(a) α-type silicon nitride accounts for 80% by weight or more, and the oxygen content is 2.0 to 5.5% by weight and the content of metals other than silicon is 1% by weight as metals. Silicon nitride thread powder having a weight of less than 99.8 to 70 weight, (b) Periodic Table H
A silicon nitride yarn sintered body comprising: (c) 0.1-10% by weight of an oxide powder of an a-series element; and (c) 0.1-20% by weight of an aluminum oxide powder. 2(a) Nitriding in which α-type silicon nitride accounts for 80% by weight or more, oxygen content ranges from 2.0 to 5.5% by weight, and the content of metals other than silicon is 1% by weight or less as metals. A mixture containing silicon thread powder 99.8 to 70% by weight, (b) oxide powder of 1a group elements of the periodic table 0.1 to 10% by weight, and (C) aluminum oxide powder 0.1 to 10% by weight. 9/1700~ under pressure of 300~650
A method for producing a silicon nitride yarn sintered body, characterized by pressure sintering at 1830°C.