JPS61155262A - Silicon nitride sintered body and manufacture - 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 (Field of Industrial Application) The present invention relates to a silicon nitride sintered body having excellent oxidation resistance at high temperatures and excellent contract strength at high temperatures, and a method for producing the same.

(Prior art) Conventionally, materials to which rare earth element oxides are added have been commonly used as high-temperature, high-strength silicon nitride materials.The reason for this is that the rare earth element oxides and silicon nitride This is because a grain boundary structure having a melting point is formed between the silicon nitride particles through the reaction, so that the strength of the sintered body as a whole does not decrease even at high temperatures.

However, when such rare earth element-added silicon nitride sintered bodies are used in an oxidizing atmosphere at high temperatures for a long time, they become oxidized and, for example, l+e2si303N4→R'
A rare earth silicate is produced by a reaction such as e2Si207, and since the silicate has a high melting point, it becomes a powder and does not serve as a protective film to seal the surface layer of the sintered body.

Therefore, oxidation progresses to the inside of the sintered body, and such a silicon nitride sintered body becomes inferior in oxidation resistance at high temperatures.

In order to solve this problem, in the past, rare earth 10 alumina or rare earth 10 silica threads were added, but in this case, for example, although an improvement in oxidation resistance at 1200°C, i, was observed, At higher temperatures (approximately 14,00°C), a sufficient effect on oxidation resistance cannot be achieved, and furthermore, these additives form a grain boundary structure phase between silicon nitride particles whose melting point is not very high. As a result, problems such as a decrease in the high temperature strength of the sintered body arise.

(Means for Solving the Problem) In view of the above, the inventors of the present invention, after intensive research, have determined that the grain boundary AIL texture is crystalline and partially glassy.
1'103 (a.

1co1-3) and β-3 by XR diffraction! J+(210
) where the peak ratio of the Re2Si303N4(211) peak to the Re2Si303N4(211) peak is less than about 10%.
303N < (melilite compound) and β-3i, N
, and the remainder, the silicon nitride sintered body has dramatically improved high-temperature oxidation resistance without deteriorating its high-temperature strength, The present invention has been accomplished.

That is, the sintered body of the present invention has silicon nitride in periodic table I
II A silicon nitride sintered body obtained by adding and mixing an oxide of at least one element among group a elements and tungsten or a tungsten compound other than tungsten carbide and firing the mixture, the sintered body structure being , crystalline and some glass trade a Re2O3・b WO,, (a+b= 1~3)
and fle2si303N to β-3i3N4 (210) peak by X-ray diffraction, Re2S whose peak ratio of (2]1) peak is less than 10%! Grain boundary structure mainly composed of zOJ+ (melilite compound) and β-9i3N4 and 1
, the remainder consists of β-3iaN<particles, and the high temperature oxidation resistance is 0.03 to 1.0τ at 1300°C for 100 hours.
The present invention is a silicon nitride sintered body with excellent high-temperature oxidation resistance, characterized by a relative specific gravity of n H/mm 2 and theoretical density of 90% or more.

Next, the basic technical matters related to the present invention will be explained.
It lies in the following points.

(1) When tungsten or tungsten compounds (excluding carbides) are added in a certain composition range together with oxides of elements of group IIIa of the periodic table, a low melting point composition of silicate of group IIIa of the periodic table of elements and tungsten is first added in the firing process. Densification progresses easily for generation. (2) By further increasing the temperature, the tungsten compound becomes a high melting point composition compound, such as a Re2O3・l) WO3 (a, b
= 1-3). (3
) Therefore, even if it becomes a sintered body, the high temperature strength will not deteriorate.

That is, when this sintered body is exposed to an oxidizing atmosphere, 1 l
For example, 1200
In the temperature range up to °C, tungsten oxide and silicate form a dense protective film, improving oxidation resistance. Next, in response to oxidation in a high temperature range (approximately 1400°C), l1103 is dispersed from the silicate protective film,
Since the oxygen ion diffusion resistance of the remaining silicate-retaining RIM is increased, even at high temperatures, the Al2
This means that it does not deteriorate the oxidation resistance of the sintered body unlike Q and SiQ□.

By the way, the mechanism by which the oxidation resistance of the sintered body is increased by adding tungsten or a tungsten compound as an additive to silicon nitride has not been completely elucidated, but the mechanism is as follows.
(a) The silicon oxide produced by the oxidation of silicon nitride reacts with the added rare earth oxide to facilitate the formation of a homogeneous glassy film, and (b) then the SiO□-Re2
0. 10. (Produced when tungsten or tungsten compounds are oxidized)
Because it has a relatively low melting point and boiling point, it gradually volatilizes and disperses from its glassy coating due to commercial processing, and the coating that remains on the surface of the silicon nitride sintered body is a rare earth glass with a high melting point. This is thought to be due to the effect of sealing the surface and suppressing oxygen intrusion into the interior.

Since the remaining high-melting-point rare earth glass has a small oxygen diffusion coefficient, once a film is formed, it acts as a strong barrier film against subsequent reactions with oxygen, thereby improving the oxidation resistance of the sintered body. It is thought that this will improve the

Furthermore, in the present invention, tungsten carbide is excluded from among the tungsten compounds; however, the addition of tungsten carbide deteriorates the sinterability, and also causes the problem of deteriorating the oxidation resistance and thermal shock resistance of the sintered body. It is from. That is,
When the green compact of WC+Si3N and +Re2O3 is sintered,
Si, N4 and Re20. It promotes the reaction of
2Si, 0-N- (melilite compound) is mainly produced (the peak ratio of Re5i = 0, N, (211) to the β-5i3N, (210) peak in the sintered body exceeds 10%), and as described above. As shown, Re2Si, OJ4→Re2S
A reaction like i20□ produces a rare earth silicate, which has a high melting point and becomes a powder, which seals the surface layer of the sintered body. Does not form a film. It is thought that this results in a rather poor oxidation resistance and high-temperature strength.

Note that the amount of grain boundary structure in the sintered body of the present invention is about 5 to 2.
15% by volume, and the silicon nitride particle diameter is within the range of about 1 to 20 μm.

Next, the present invention provides a manufacturing method for obtaining the silicon nitride sintered body.

That is, at least one of the Group IIIa elements of the periodic table.
The total amount of oxides of certain elements and tungsten compounds other than tungsten or tungsten carbide is not more than 20% by weight (however, the amount of oxides of at least one element in Group 11a of the Periodic Table of Elements is not more than 18% by weight) ) and the remainder is silicon nitride in a nitrogen atmosphere.
Provided is a method for producing a silicon nitride sintered body having excellent high-temperature oxidation resistance, which is characterized by firing at 500 to 2300°C.

Here, the oxide of group IIIa element of the periodic table is 18% by weight.
If the temperature exceeds 100%, the formation of silicates of elements in group 11ja of the periodic table increases, and the surface of the sintered body becomes powdery, making it difficult to form an oxidation-resistant protective film. This will result in an extreme deterioration of sexuality.

Furthermore, if the amount of tungsten added exceeds 20% by weight, a large amount of W oxide in the dense oxidation-resistant silicate film dissolves into solid solution, lowering the melting point and causing negative effects such as foaming, which may affect the oxidation resistance and Mechanical strength deteriorates. Also, the firing temperature is 15
Below 00°C, the densification of the sintered body is insufficient, and 23
(If the temperature exceeds 10°C, β-Si, N.

Abnormal grain growth occurs, and high-temperature strength deteriorates severely.

Therefore, numerical limitations are made as described above.

Next, a summary of Examples and Comparative Examples of the present invention will be described as [-Test Example].

(Test Example 1) The table shows data on sintered bodies obtained by blending silicon nitride with various rare earth element oxides and tungsten or tungsten compounds in various proportions.

In this test example, silicon nitride had an average particle size () of 6 μm.
Using aS i 3N * of No. 1, each compounded component was blended in the ratio shown in Table 1, urethane balls were added using an ethanol medium, and after dispersion mixing for 24 hours, the resulting mixed powder was mixed as a binder. Paraffin wax was added and granulated, and molded with a molding pressure It/era 2. The obtained molded body was fired under the firing conditions shown in B in Table 1.

In addition, sample numbers (4), (9), (10) in Table 1
Regarding c), (12) and (14), the green compact of each sample was treated with an oxide of an NLA group element of the periodic table and a compound (11
After being fired to ensure a sufficient reaction with other components (excluding IC), they were further fired by the firing method shown in Table B of Table 1.

The high-temperature strength was measured using a 0.3+n+n C surface treatment on a test piece ground to a size of 3 x 4 x 40 ram, and using a four-point bending method specified in JIS R-1601.

The weight gain due to oxidation was expressed as the weight gain obtained by holding the JIS bending test piece in the atmosphere at 1300° C. for 1100 hours divided by the surface area of the test piece. In addition, in the table, G 11S is gas pressure sintering method, Pl is normal pressure sintering method, 11P is hot press sintering method, II I P 1. means the hydrostatic hot press sintering method.

In Table 1 of the obtained molded bodies, sample numbers 3 to 16.18 and 19 are in the composition range of the present invention, and the oxidation weight gain (130 (1°C, 100 hrs) is 0°05 to 1
, (l mB/cm2 value, very good oxidation resistance, and high temperature strength of 80 Kg/+n+n2 at 1300℃
Above, at 1400°C, the weight was 60 kg, 8◎1 to 2 or more, which is good.

In sample numbers 1 and 2, Si3N is less than 80% by weight, the total amount of oxides of elements of group IA in the periodic table and W or W compounds exceeds 20% by weight, and the oxidation weight increase is 2.
, 5 m (more than 3/c1o2, high temperature strength is also 35 K[?
/+nm2.

For sample number 17, Si3N is 80% by weight or more,
Periodic Table II The total amount of group a element oxides and - compounds is 20
% by weight or less, - the compound is a carbide,
Therefore, the oxidation weight increase is 2,50 +++g/cm2 (
The high temperature strength was 565/aun2 at 130()°C, which was extremely low.

Furthermore, as shown in B of Table 1, sample number 10a and ]O
f has a similar composition range but a firing temperature outside the range of the present invention, and the firing temperature is 1450 °C below 1500 °C.
As shown in Table 1, sample number 10a has a low relative specific gravity of 75% of the theoretical density, indicating insufficient sintering (therefore, oxidation weight gain and high temperature strength were not measured).

In addition, abnormal grain growth occurs in sample number 10f, where the firing temperature is 2350°C, which exceeds 2300°C.
High temperature strength at 1300℃ and 1400℃ is 63K B
/ +n to 2 and 58KFi/III Ill
It is understood that it is inferior to 2.

Also, sample numbers (4), (9), (10c), (12)
and (14) in the first firing, periodic table I
It is thought that the oxidation resistance and high temperature strength are slightly improved because the reaction between the oxide of the IIa group element and the - or - compound is carried out sufficiently. In addition, in test example 2,
The silicon nitride particle diameters of the sintered bodies of sample numbers 8 to 11, in which the firing method was IIs, were 5 to 10 μIn;
2.16. Those of 17 and 18 were 5 to 20 μm. In addition, the particle size according to the method is: (-15, II P
, II I P method 1-10. IJ+n.

(Test Example 2) Sample numbers 3 to 10.10b-]Oe, 1 of Test Example 1
X-ray diffraction was performed on 1-17.18 and 19, and β-3i, N, (210) peaks and Re2Si3 in the sintered body were
Table 2 shows the results of comparing the peak ratios with the 03N and (211) (melilite compound) peaks. As can be seen from Table 2, sample number 17, which had the same composition but added EnC, was β-3i3N, Re2Si3
0. The peak ratio of N is as high as 10%, and the oxidation resistance and tooth temperature strength are significantly inferior when compared with those with a peak ratio of less than 10% in which a compound other than WC or - is added.

171 (Effects of the Invention) According to the present invention, the high temperature oxidation resistance is improved by increasing the oxidation weight (
1300℃, 100 hours) is 0.05-1. O+oB/
cm2, high temperature strength is 80 KB/+ at 1300℃
This provides a silicon nitride sintered body with excellent n+o2, no decrease in strength at high temperatures, and excellent high-temperature oxidation resistance.

Therefore, the obtained sintered body is suitable for use in gas turbines, engine parts, etc., and the usable range of silicon nitride sintered bodies can be considerably expanded, which is unprecedented. It is excellent.

Claims (5)

[Claims] (1) A silicon nitride sintered body obtained by adding and mixing an oxide of at least one element in Group IIIa of the periodic table and tungsten or a tungsten compound other than tungsten carbide to silicon nitride and firing the mixture. The structure of the sintered body is crystalline and partially glassy aRe_2O_3・bWO.
_3 (a, b = 1 to 3) and β-Si_3 by X-ray diffraction
Re_2Si_3O_ for N_4(210) peak
Re_2Si_3O_3N_4 (melilite compound) with a peak ratio of 3N_4(211) peak of less than 10%
The grain boundary structure consists mainly of and β-Si_3N_4 and the balance is β-Si_3N_4 particles, and the high temperature oxidation resistance is 0.03 to 1.0 mg at 1300°C for 100 hours.
/mm^2, a silicon nitride sintered body with excellent high-temperature oxidation resistance, characterized in that the relative specific gravity of the theoretical density is 90% or more. (2) The total amount of the oxide of at least one element in Group IIIa of the periodic table and tungsten or a tungsten compound other than tungsten carbide is 20% by weight or less (however,
The amount of oxide of at least one element in Group IIIa of the periodic table is 18% by weight or less) and the balance is silicon nitride.
A method for producing a silicon nitride sintered body with excellent high-temperature monooxidation properties, characterized by firing at a temperature of ~2300°C. (3) Place the green compact in a nitrogen atmosphere of 1 atm.
After firing at ~1500°C until the reaction between the oxide of the Group IIIa element in the periodic table and tungsten or a tungsten compound other than tungsten carbide is sufficiently performed,
The method for producing a silicon nitride sintered body according to claim 2, wherein the temperature is raised to 1800° C. and fired under normal pressure. (4) Place the green compact in a nitrogen atmosphere of 1 atm.
After firing at ~1500°C until the reaction between the oxide of the Group IIIa element in the periodic table and tungsten or a tungsten compound other than tungsten carbide is sufficient, the temperature is raised to 1500~1800°C under pressure and hot-pressed. A method for producing a silicon nitride sintered body according to claim 2. (5) Place the green compact in a nitrogen atmosphere of 1 atm.
After firing at ~1500°C until the reaction between the oxide of the Group IIIa element in the periodic table and tungsten or a tungsten compound other than tungsten carbide is sufficiently performed, the nitrogen gas pressure is set to above atmospheric pressure and the temperature is 1500~2300°C. 3. The method for producing a silicon nitride sintered body according to claim 2, wherein the temperature is raised to a temperature of 100 mL and fired under gas pressure.