JP2883234B2 - Silicon nitride sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength silicon nitride sintered body, and more particularly to an improvement for reducing variation in characteristics.

[0002]

2. Description of the Related Art Conventionally, silicon nitride-based sintered bodies have been applied to various engineering ceramics as materials having excellent high-temperature strength as high-temperature materials.

[0003] Since such silicon nitride itself is difficult to be sintered, oxides of Group 3a elements of the periodic table such as Y ₂ O ₃ and various metal oxides such as Al ₂ O ₃ have been conventionally used. Addition and firing are performed.

[0004] Recently, the operating temperature of a silicon nitride based sintered body has been expanding to a high temperature range of 1400 ° C or higher, and accordingly, improvement of the high temperature characteristics of the sintered body has been desired. Therefore,
From the viewpoint that the high-temperature characteristics greatly change due to the composition of the grain boundaries of the silicon nitride based sintered body and the melting point of the grain boundaries due to the composition,
A sintered body in which the addition of a low-melting substance such as Al ₂ O ₃ is suppressed and Y ₂ O ₃ or an oxide of a rare earth element or silicon oxide or the like is added thereto has been proposed. It has been proposed to increase the melting point of the grain boundary by changing the melting point.

[0005]

However, the above-mentioned sintered body has excellent characteristics in terms of bending strength and oxidation resistance as compared with conventional products, but the variation in characteristics has not been solved yet. There is a disadvantage that it is difficult to obtain a sintered body having stable characteristics in productivity.

[0006] Then, when the cause of this variation was investigated, it was found that an abnormal tissue was present in most of the fracture sources. Further analysis of the abnormal structure revealed that iron (Fe) was present, which caused a eutectic reaction with silicon (Si), and that the rare earth elements added around the iron (Fe) were excessively collected. .

[0007]

Means for Solving the Problems The present inventors have studied in detail a method for reducing the adverse effect of Fe as an impurity with respect to such problems, and found that W is contained at a predetermined ratio in such a system. The present inventors have found out that the addition and addition of the additive can significantly reduce the generation of the abnormal tissue, thereby improving the variation in characteristics, thereby leading to the present invention.

That is, the silicon nitride sintered body of the present invention contains silicon nitride as a main component, and contains Er, Y, Sc, Ce, Yb, and D.
0.5 mol% to 10 mol% of at least one rare earth element oxide of y, Tb and Ho, 5 ppm to 1000 ppm of Fe by weight, and 0.01 wt% to 2 wt% of W in terms of oxide Is contained at a ratio of

Hereinafter, the present invention will be described in detail. The sintered body of the present invention contains silicon nitride as a main component in composition, and further contains at least Y or a rare earth element as a sintering aid in an amount of 0.5 to 10 mol.
Although it contains 1%, there is a case where a raw material having low purity is used, or Fe is mixed in the system in the mixing step in the production process. This Fe has an amount of 5p
pm or less, it does not particularly affect the characteristics of the sintered body, but if the amount is mixed at a rate of 5 ppm or more, it becomes a source of destruction in the sintered body as described above. An abnormal structure is formed, thereby deteriorating the characteristics of the sintered body and causing variations in the characteristics.

In the present invention, it is important that W is present in a system containing 0.01 to 2% by weight, particularly 0.05 to 2% by weight, in terms of metal, in such a system containing Fe. It is. Due to the presence of W, the behavior of Fe in the sintered body can be fixed. Therefore, if the amount of W is less than 0.01% by weight, the generation of an abnormal structure cannot be suppressed, and the variation in characteristics increases. If the amount of W exceeds 2% by weight, W itself aggregates, It becomes a source of destruction and causes a reduction in the strength of the sintered body.

The effect of adding W is not sufficiently exhibited when the amount of Fe is too large, and the upper limit of the amount of Fe is 1000 ppm by weight.

In the method for producing the sintered body of the present invention, a silicon nitride powder is used as a starting material, and at least a powder of an oxide of at least Y or a rare earth element is used as a sintering aid. According to the present invention, it is important to add a compound of W to such a system at a ratio of 0.01 to 2% by weight in terms of W metal. As the W compound used,
W oxides, carbides, silicides, and the like.

These starting materials are mixed at the above-mentioned predetermined ratio and then molded by a known method. In addition to being contained in the starting materials, Fe may be mixed during the steps up to the molding step. . According to the present invention, the amount of Fe in the final compact is 5 to 200 in terms of metal in consideration of the amount of these contaminants.
It is necessary to control to 0 ppm. As the molding means, press molding, extrusion molding, injection molding, casting molding, cold isostatic molding and the like can be mentioned.

Next, the molded body is fired at 1600 to 2000 ° C. in a non-oxidizing atmosphere such as nitrogen by firing means such as normal pressure firing, nitrogen gas pressure firing, and hot press firing. In the case of the hot isostatic firing method as a special firing method, after densification to a theoretical density ratio of 95% or more by the above method,
In an atmosphere containing 2,000 to 2,000 atmospheres of nitrogen.
A method of baking at 00 to 2000 ° C., or applying BN to the surface of the molded body, and then applying glass powder to the surface, enclosing the glass powder in a capsule, or filling the inside with glass powder. After filling in a heat-resistant container, the glass was melted at a high temperature to form a glass seal.
A method of baking at 1600 to 2000 ° C. under ２０００2000 atm is adopted.

In the present invention, the amount of the Y or rare earth element in terms of oxide is limited to 0.5 to 10 mol%. If the amount is less than 0.5 mol%, a sufficient dense body cannot be obtained, This is because, if it exceeds 300, mechanical properties such as high-temperature strength deteriorate. Y or the rare earth element includes at least one of Y, Er, Sc, Ce, Yb, Dy, Tb, and Ho.

Further, according to the present invention, Al ₂ O ₃ , MgO, CaO, AlN, ZrO ₂ , Si
Be such as O ₂ was added at a rate of 10 wt% or less but those not any effect to the effect of the present invention, among these, Al ₂
When low-melting substances such as O ₃ , MgO and CaO are present, Fe
The characteristics of the present invention are not significantly deteriorated, so that the constitution of the present invention is effective particularly in a composition system in which these low melting point substances are 1% by weight or less, particularly 0.5% by weight or less.

[0017]

According to the present invention, when Fe is present in a system, silicon nitride is decomposed in a sintering process, and a eutectic reaction with generated Si occurs. Rare earth elements are excessively collected around the Fe-Si eutectic reaction product to form an unusual abnormal structure.

For these behaviors, if W exists,
The above behavior of Fe is reduced. The reason for this is not clear, but W forms a compound such as silicide in the sintering process, and Fe is positively dissolved in this compound, so that the Fe element becomes inactive and silicon nitride is formed. It is considered that the decomposition of is suppressed, and as a result, the production of the Fe-Si eutectic reaction product is suppressed.

Thus, since the fracture starting point of the sintered body is caused by an abnormal structure due to the presence of Fe, the surface of the sintered body is always on the surface of the sintered body, so that the characteristics of the sintered body are improved, and the variation is reduced. A silicon nitride-based sintered body can be produced.

Further, the characteristics of the sintered body can be stabilized even when an inexpensive silicon nitride raw material having relatively low purity is used due to the above-described addition effect of W, so that the cost of the sintered body can be reduced. You can also plan.

[0021]

EXAMPLES Silicon nitride raw material (oxygen content 1.0%, BET specific surface area 10 m ² / g, α rate 98%, Fe content 30 pp)
m) and Y ₂ O ₃ , Yb ₂ O ₃ , Sc ₂ O as sintering aids
_{3, Er 2 O 3, Ho} 2 O 3, Dy 2 O 3, CeO 2,
Each of the powders of Tb ₂ O ₃ was weighed at the ratios shown in Table 1 and then placed in a polypot and mixed with silicon nitride balls for 72 hours using methanol as a solvent. After drying the obtained mixture, it is granulated, and 80 mm × 45 mm × 5 mm
And press molded. The Fe amount of the obtained molded body was measured by ICP emission spectroscopy. Then, each compact was fired at a temperature shown in Table 1 in an atmosphere of a nitrogen gas pressure of 10 atm. In the table, for sample No. 16, BN was applied to the surface of a molded body having the composition shown in Table 1, and the sample was placed in a glass bath.
Firing was performed at 600 ° C. under a pressure of 2000 atm.

Elemental analysis of the obtained sintered body confirmed that the composition after sintering was not substantially different from the composition of the molded body. In addition, a test piece of 20
Each piece was cut out, the bending strength at room temperature was measured by JISR1601, and the average value was examined. Furthermore, the fracture source was examined from the fracture surface of the bent piece, and the number of fracture sources whose abnormal grain growth was caused by iron was examined. The results are shown in Table 1.

[0023]

[Table 1]

As is clear from Table 1, in the sample No. 1 in which W was not added at all under the above-mentioned conditions and the content of impurities of several tens of ppm was mixed in the production under the above conditions, the source of the destruction was Many are due to the abnormal structure of Fe-Si, and some of them have very low strength of 460 MPa.

On the other hand, when a W compound is added, 0.1% is obtained.
With the addition of 01% by weight, as shown in Sample No. 2, the ratio of the sintered body broken by the abnormal structure decreases, and as the amount of W increases, the average strength recovers and the dispersion of characteristics improves. It can be understood that it is done. However,
In Sample No. 10 in which the amount of W exceeds 2% by weight, agglomeration due to W was observed, thereby deteriorating the strength.

In order to confirm the effect of adding W, an evaluation was made on a system in which Fe was added to the system to increase the amount of Fe.
In samples No. 9 to 9, the effect of adding W was reduced, and in Sample No. 9, a decrease in strength was also observed.

Further, when the addition amount of Y ₂ O _{3 in} the sintered body was changed, the densification was not sufficiently achieved in the sample No. 11 in which the addition amount was less than 0.5 mol%, and 10 mol% was not achieved. When the ratio exceeded, deterioration in strength was observed.

The effect of the present invention can be obtained even when the firing conditions are hot isostatic pressing. Even when WSi ₂ or WC other than WO ₃ is used as the W compound, other rare earth elements can be used. A similar effect was also observed.

[0029]

As described above in detail, according to the present invention, F
By adding W to the system containing e, the generation of an abnormal structure due to Fe is suppressed to reduce the destruction due to the abnormal structure, and a sintered body having high strength and no variation in characteristics can be manufactured.

Claims (1)

(57) [Claims] 1. A method according to claim 1, wherein the main component is silicon nitride, and Er, Y, Sc,
0.5 mol% to 10 mol% of at least one rare earth element oxide of Ce, Yb, Dy, Tb and Ho;
A silicon nitride-based sintered body containing Fe in a weight ratio of 5 ppm to 1000 ppm and W in an amount of 0.01% by weight to 2% by weight in terms of oxide.