JPH07206527A - Silicon nitride-based sintered compact and its production - Google Patents

Abstract

PURPOSE:To improve high-temperature strength of a silicon nitride-based sintered compact by blending silicon nitride with aluminum oxide and ytterbium oxide in a prescribed ratio and then sintering the blend. CONSTITUTION:This silicon nitride sintered compact is produced by forming mixed powder containing 70-97wt.% of silicon nitride powder, 2-30wt.% of ytterbium oxide powder and <=5wt.% of aluminum oxide powder and having >=5 weight ratio of ytterbium powder to aluminum oxide powder and then, sintering the formed material in a nitrogen gas atmosphere at 1700-2100 deg.C for <=9hr. In this reaction, impurities of these elements each is kept to <=100ppm. In this invention, since a boundary part of the silicon nitride sintered compact is packed with an Yb-Si-O-N based or an Al-Yb-Si-O-N based oxide nitride glass phase having high high-temperature characteristics, produced by reaction with a component added as an auxiliary, a silicon nitride-based sintered compact hardly lowering strength in high temperature load and excellent also in oxidation resistance can inexpensively be produced by a conventional ordinary pressure sintering method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride-based sintered body for use in mechanical parts which are required to have high temperature, high strength, oxidation resistance, wear resistance and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Since a silicon nitride sintered body is a difficult sintered body,
A method of sintering by adding aluminum oxide, yttrium oxide, etc. as a sintering aid is used, but these auxiliary components remain at the grain boundaries as a glass phase after sintering, and this glass phase softens at high temperature. It is known that by doing so, the high temperature characteristics are degraded. In order to improve the high temperature strength, the absolute amount of the auxiliary agent should be reduced and hot pressing or HIP
Forcible sintering is carried out by a special method such as, but almost no effective countermeasures are taken for oxidation resistance.

[0003]

DISCLOSURE OF THE INVENTION The present invention uses ytterbium oxide or a mixed system of ytterbium oxide and aluminum oxide as a sintering aid, and optimizes the amount and composition ratio of the ordinary atmospheric pressure baking. An object of the present invention is to provide a silicon nitride sintered body which is densely sintered even if it is bonded and has little deterioration in high temperature characteristics such as high temperature strength and oxidation resistance, and a method for producing the same.

[0004]

The present invention provides (1) a silicon nitride-based sintered body characterized by containing 70 to 97% by weight of silicon nitride and 2 to 30% by weight of ytterbium oxide. (2) Silicon nitride powder: 70 to 97% by weight and ytterbium oxide powder: 2 to 30% by weight, mixed powder is molded and sintered at 1700 to 2100 ° C. in a nitrogen gas atmosphere. A method for manufacturing a silicon-based sintered body. (3) Silicon nitride: 70 to 97% by weight, ytterbium oxide: 2 to 30% by weight, and aluminum oxide: 5% by weight or less, a silicon nitride-based sintered body. (4) Molding a mixed powder of silicon nitride powder: 70 to 97% by weight, ytterbium oxide powder: 2 to 30% by weight, and aluminum oxide powder: 5% by weight or less, and firing at 1700 to 2100 ° C. in a nitrogen gas atmosphere. A method for manufacturing a silicon nitride-based sintered body, comprising: (5) Silicon nitride: 70 to 97% by weight, ytterbium oxide: 2 to 30% by weight and aluminum oxide: 5% by weight or less, and the weight ratio of ytterbium oxide to aluminum oxide is 5 or more. A characteristic silicon nitride sintered body. (6) Silicon nitride powder: 70 to 97% by weight, ytterbium oxide powder: 2 to 30% by weight and aluminum oxide powder: 5% by weight or less, and the weight ratio of the ytterbium oxide powder to the aluminum oxide powder is 5%. The mixed powder consisting of the above is molded and then molded in a nitrogen gas atmosphere.
A method for producing a silicon nitride-based sintered body, which comprises sintering at 00 to 2100 ° C. Is.

[0005]

According to the present invention, a Yb-Si-O-N system or Al-Yb-S system having high temperature characteristics, which is generated as a result of the reaction of the component added with the grain boundary portion of the silicon nitride sintered body as an auxiliary agent, is obtained.
By filling with the i-O-N-based oxynitride glass phase, a silicon nitride-based sintered body having high reliability with little decrease in strength under high temperature load and excellent in oxidation resistance can be obtained. It can be provided at low cost by manufacturing it by the atmospheric pressure sintering method.
The reason for limiting the numerical values according to the present invention will be described below.

(1) Silicon Nitride: 70 to 97% by Weight Silicon nitride powder is a main agent for producing a silicon nitride sintered body. If it is less than 70% by weight, the amount of the auxiliary agent is relatively large. As a result, the deformation becomes remarkable during sintering, strength cannot be exhibited at room temperature and high temperature, and all the excellent mechanical properties that are general features of the silicon nitride sintered body are lost. On the other hand, if it exceeds 97% by weight, the amount of the auxiliary agent becomes relatively small, and even if the amount is such that the sinterability is not a problem, high temperature strength cannot be exhibited. More preferably, it is 76 to 92% by weight.

(2) Aluminum oxide: 5% by weight or less Aluminum oxide reacts and melts with ytterbium oxide and silicon oxide existing as an oxide layer in the silicon nitride powder at a temperature near the sintering temperature to assist in the production of a silicon nitride sintered body. It acts as an agent and contributes to densification, but also has the effect of reducing high temperature strength. Therefore, in order not to reduce the high temperature strength, it is preferable to reduce the amount of aluminum oxide, that is, it is preferable not to add it. However, if it is not added, the sintering becomes insufficient and the absolute value of the strength becomes low. If it exceeds 5% by weight, the sinterability is good and the composition is sufficiently densified, but the high temperature strength is significantly reduced. More preferably, it is 0.2 to 2.2% by weight.

(3) Ytterbium oxide: 2 to 30% by weight Ytterbium oxide reacts and melts with aluminum oxide and silicon oxide existing as an oxide layer in the silicon nitride powder near the sintering temperature to produce a silicon nitride sintered body. It acts as an auxiliary agent and has the effect of preventing the deterioration of high temperature strength. Further, even if aluminum oxide is not used, only ytterbium oxide and silicon oxide act as an auxiliary agent under highly controlled conditions. In this case, since the amount of the metal element is reduced by one, the eutectic temperature is further increased, and the effect of preventing the decrease in high temperature strength is high. Therefore, if it is less than 2% by weight, the sinterability is deteriorated, it is difficult to sufficiently densify, and the high temperature strength is remarkably reduced. If it exceeds 30% by weight, the amount of aluminum oxide is relatively small, the sinterability is lowered and the strength is lowered. More preferably, it is 3.2 to 23% by weight. In addition, it is preferable that all the above raw materials have an average particle diameter of 2 μm or less.

(4) Weight ratio of ytterbium oxide powder to aluminum oxide powder: 5 or more Ytterbium oxide and aluminum oxide react and melt near the sintering temperature, and act as an auxiliary agent during the production of a silicon nitride sintered body, and then burned. After binding, it exists mainly as a glass phase in the grain boundaries and controls the high temperature characteristics. When this ratio is less than 5, the high temperature strength decreases. If this ratio is too large,
Since the sinterability decreases, it is more preferably 10 to 20.

(5) Impurities may be any element 10
0 ppm or less is desirable.

(6) Nitrogen gas atmosphere The nitrogen gas pressurized atmosphere is used to prevent silicon nitride from sublimating at high temperature. If the pressure exceeds 10 kg / cm ² , the high pressure gas control method will apply the gas
It is disadvantageous in the actual production of the product because it is subject to strict regulations regarding the handling of containers, and it also increases the cost.
It is preferably less than kg / cm ² . More preferably 6-9.
It is 9 kg / cm ² .

(7) Firing at 1700 to 2100 ° C. The ceramic material is produced by baking and sintering powder. Although firing is required at the time of sintering, in the case of silicon nitride, although an auxiliary agent is added to facilitate sintering, it is basically difficult to sinter and a high firing temperature is required for sintering. Becomes At a temperature of less than 1700 ° C, the auxiliary agent does not react or melt, so that it hardly sinters and does not densify. Again 21
If the temperature exceeds 00 ° C., the silicon nitride sublimes and similarly does not densify. More preferably 1750-195
It is 0 ° C.

(8) Firing time The firing time is not particularly limited, but when firing a ceramic material, if a normal external heating furnace is used, a difference in temperature between the surface and the inside of the sample causes a considerable temperature difference. Therefore, it is necessary to maintain the temperature for some time after the temperature is raised to the target temperature. Even if it is held for 10 hours or more, the sintering does not proceed so much, and it is meaningless from the viewpoint of cost. It is more preferably 9 hours or less.

[0014]

EXAMPLE The raw material powder used in the test was a high-purity powder of silicon nitride raw material powder having an average particle diameter of 0.5 μm (crystallite diameter of 0.2 μm or less), and the sintering aid ytterbium oxide had an average particle diameter of 0.5 μm. 1.2 μm powder and aluminum oxide powder having an average particle size of 0.8 μm were used. The compounding ratio of each powder is as shown in Table 1. For all tests in this example, a polyethyleneimine-based dispersant was used.
Wet mixing using 1-butyl alcohol as a solvent,
According to the crushing method.

In producing a silicon nitride sintered body, first, for mixing, 2.1% by weight of a polyethyleneimine-based dispersant and 100% by weight of raw material powder, and 1-butyl alcohol solvent 3 are mixed.
3.3% by weight was added, and the mixture was uniformly mixed using zirconia balls, then dried and pressed with a diameter of 60 mmφ, about 6 mm.
And was hydrostatically pressed at a pressure of 4 t / cm ² to obtain a molded body. This molded body was heated to 500 ° C. in a vacuum, held for 1 hour to degrease, and then nitrogen gas 9.9 k
1800 at 1 ° C / min under pressure of sq.cm.
The temperature was raised to ˜1900 ° C. and sintered for 4 hours. Table 1 shows the high temperature strength of the sintered body according to the present invention produced under these conditions. According to this, compared with Table 2 showing the high temperature strength of the sintered body by the conventional method, the decrease in high temperature strength is significantly suppressed, the oxidation resistance is also improved, and the reliability at high temperature is increased. It became a thing.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

EFFECTS OF THE INVENTION According to the present invention, a decrease in high temperature strength can be significantly suppressed, and a silicon nitride sintered body having high high temperature strength can be provided at a low cost by a very general manufacturing method. Is big.

Claims (6)

[Claims] 1. A silicon nitride-based sintered body comprising silicon nitride: 70 to 97% by weight and ytterbium oxide: 2 to 30% by weight. 2. A mixed powder consisting of 70 to 97% by weight of silicon nitride powder and 2 to 30% by weight of ytterbium oxide powder is molded and molded in a nitrogen gas atmosphere at 1700 to 2100 ° C.
A method for manufacturing a silicon nitride sintered body, comprising: 3. Silicon nitride: 70 to 97% by weight, ytterbium oxide: 2 to 30% by weight, and aluminum oxide: 5
A silicon nitride sintered body characterized by containing less than or equal to wt%. 4. A mixed powder comprising silicon nitride powder: 70 to 97% by weight, ytterbium oxide powder: 2 to 30% by weight, and aluminum oxide powder: 5% by weight or less is molded and molded in a nitrogen gas atmosphere at 1700 to 2100 ° C. A method for manufacturing a silicon nitride sintered body, comprising: 5. Silicon nitride: 70 to 97% by weight, ytterbium oxide: 2 to 30% by weight, and aluminum oxide: 5
A silicon nitride sintered body containing less than or equal to 5% by weight and having a weight ratio of ytterbium oxide to aluminum oxide of 5 or more. 6. A silicon nitride powder: 70 to 97% by weight, a ytterbium oxide powder: 2 to 30% by weight, and an aluminum oxide powder: 5% by weight or less, and a weight ratio of the ytterbium oxide powder to the aluminum oxide powder. 5. A method for producing a silicon nitride sintered body, which comprises molding a mixed powder of 5 or more and sintering at 1700 to 2100 ° C. in a nitrogen gas atmosphere.