JPH0230672A - Silicon nitride ceramic sintered compact and production thereof - Google Patents

Abstract

PURPOSE:To inexpensively obtain the title sintered compact having high density, strength and toughness in good productivity by blending Si3N4 with specific amounts of CeO2 and HfO2, molding the blend and heat-treating the moldings in two stages in a non-oxidizing gas atmosphere containing nitrogen under prescribed conditions. CONSTITUTION:A silicon nitride powder is blended with 0.1-10wt.% cesium oxide and 0.1-10wt.% hafnium oxide used together as sintering auxiliary. Then the blend powder is molded and the obtained moldings are retained in a non- oxidizing gas atmosphere at 1,500-1,650 deg.C for >=1hr and at 1,700-1,780 deg.C for >=2hr and sintered to provide the silicon nitride ceramic sintered compact. Furthermore, silicon nitride ceramic sintered compact further densified can be produced by sintering in operation of two stages carrying out above- mentioned sintering and then further raising the sintering temperature to 1,780-2,000 deg.C in a non-oxidizing gas atmosphere containing nitrogen having >=10 atom pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a ceramic sintered body containing silicon nitride as a main component and a method for manufacturing the same, and in particular has a high ratio (relative density) to the theoretical density during sintering. The present invention relates to a sintered body that has high mechanical strength at high temperatures and high fracture toughness, and a method for producing the same.

Among conventional ceramic sintered bodies, silicon nitride ceramics have high mechanical strength in an oxidizing atmosphere from room temperature to 1200°C, high flexural strength, high toughness, and high thermal shock resistance. Furthermore, it has a wide range of uses as a low specific gravity ceramic with excellent wear resistance.

Until now, attempts have been made to obtain sintered bodies with high density and high mechanical strength by sintering silicon nitride ceramics in a non-oxidizing atmosphere at normal pressure, by heating and sintering them as they are after forming. Various attempts have been made.

For example, as disclosed in Japanese Patent Publication No. 58-49509, sintering aids such as Y2O3, M, 03, MgO, etc. are often added. However, with these sintering aids, the mechanical strength deteriorates significantly at high temperatures, and crystallization of the glass phase is considered a technical problem.

Problems to be Solved by the Invention The present invention has properties of high density, high toughness, and high bending strength using the pressureless sintering method, and also solves the above problems, and is mechanically stable even in high temperature oxidizing atmosphere. It is an object of the present invention to provide a silicon nitride ceramic sintered body with a small decrease in strength and a manufacturing method according to item 7.

Therefore, as a combination of sintering aids, cerium oxide 0.
1-10% by weight and hafnium oxide 0.1-10% by weight
was found to be effective in solving this problem.

Means for Solving the Problems The present invention provides a silicon nitride sintered body comprising 1 to 10% by weight of cerium O, 0.1 to 10% by weight of hafnium oxide, and the remainder silicon nitride, and a method for producing the same. It is.

Function Both cerium oxide and hafnium oxide used in the present invention have the function of promoting crystal phase transition from α phase to β phase in the melt during sintering of silicon nitride.

If the total content of these components exceeds 20% by weight, the mechanical strength of the obtained sintered body will decrease, and if the total content of these compounds is less than 5ffi%, the melt will be insufficient and difficult to obtain under normal pressure. Since densification does not occur, the total amount of cerium oxide or hafnium oxide is preferably 5 to 15% by weight, and if the amount of each of cerium oxide or hafnium oxide is more than 10% by weight, the melting resistance at high temperatures will be significantly deteriorated. That is, when cerium oxide is 0.1% by weight, hafnium oxide is 4.9% by weight.
or above, or conversely, when hafnium oxide is 0.1% by weight, it is preferable to make cerium oxide 4.8% by weight or more.As a result, it is possible to achieve densification comparable to that of a sintered body made by hot pressing, and a high temperature and high temperature. It will have strength.

The method for producing a ceramic sintered body of the present invention includes adding cerium oxide in an amount of 0.1N10ffi and fused l\fnium in an amount of 0.1N.
1~! The method is characterized in that a mixed powder consisting of silicon nitride in the weight percent of O and the remainder is molded, and the molded body is sintered in a non-oxidizing gas atmosphere containing nitrogen.

In the method of the present invention, these components are mixed, for example, in a planetary mixer using a pot e-ball of silicon nitride or silicon carbide, using a low boiling point solvent such as 7 setone and n-hexane. A known organic or inorganic polymeric molding agent is added to the mixed powder, or the mixture is press-molded into a molded article of a predetermined shape without any additives. The molding method is a known molding method. For example, in the case of a plate-shaped object,
Car molding pressure: 10G" 100,100O/c+s2. Secondary isostatic pressing pressure: 2000-7000kgf/cm2.

This molded body is heated and sintered at 1500 to 2000°C to obtain a sintered body. At this time, cerium oxide and hafnium a oxide are melted at 1500 to 1850° C., and in order to uniformly distribute this liquid phase, the melt is maintained for one hour or more to sufficiently wet the silicon nitride.

Further, silicon nitride is dissolved in the liquid phase at 1700 to 1780°C and reprecipitated, causing a phase transition and sintering. During this dissolution-re-precipitation process, it is necessary to hold for 2 hours or more because there is a solid solubility limit in the melt.

Preferably, the non-oxidizing gas atmosphere containing nitrogen is pure nitrogen or a mixed gas with nitrogen containing a small amount of hydrogen or ammonia.

Moreover, preferably! Pressurize the atmosphere to more than O atmosphere 178
There is a two-step sintering method in which the temperature is raised from 0 to 2000°C. This one
The meaning of performing higher temperature sintering at 05E pressure or higher is:
Silicon nitride, which decomposes under normal pressure, is suppressed from decomposition due to thermal equilibrium theory, and moreover, the bores in the sintered body diffuse and escape from the surface, making it possible to achieve greater densification. 2000℃
If the temperature is higher than 100, it is necessary to use the ultra-high pressure HIP method of 100 atmospheres or more. Note that both methods differ from the hot press method in that the shape during molding is maintained.

As described above, the sintered body obtained according to the present invention has a high relative density of 98.5% or more and a bending strength of 80 kg at room temperature.
High strength of f/ms” or more, thermal shock resistance (ΔT) of 5
Silicon nitride ceramic with high toughness of 50 or higher.

It's Kusu. These characteristic values can be easily obtained without hot pressing at normal pressure in a nitrogen atmosphere or under nitrogen pressure, making it possible to produce silicon nitride ceramics in large quantities. Hereinafter, the present invention will be explained in more detail using examples.

Example 1 Each component was blended at a predetermined blending ratio (wt%) as shown in the t51 table, and after adding an appropriate amount of acetone, each was mixed for 24 hours in a silicon nitride ball mill and evaporated to dryness to form a mixed powder. was obtained and molded.

The silicon nitride powder manufactured by Ube Industries, Ltd. had a gelatinization rate of 97% or more and an average particle size of 0.5 ILm. The cerium oxide used was OJpm, an average particle size manufactured by Shin-Etsu Chemical Co., and the hafnium oxide was manufactured by Kojundo Kagaku Co., Ltd. and had an average particle size of 3ILm.

The obtained mixed powder was molded into one car under a molding pressure of 10QOkgf/cm.
``It was molded into a plate-shaped body of 50 layers x 50 mm x 1 Q mm using hydrostatic pressure of 7000 kgf/as2.
After removing adsorbed water, residual solvent, etc. at 200℃,
The temperature was raised to 0°C at a rate of 10°C or less per minute and maintained at this temperature for 2 hours. As a result, the liquid phase is uniformly generated and distributed, making it easier to dissolve and reprecipitate the α-phase silicon nitride.

Furthermore, the temperature was raised to 1750°C at a rate of 10 to 50°C per minute, and maintained at this temperature for 2 hours or more. Then, the temperature decrease rate is 10℃ per minute.
The mixture was kept at a temperature below and slowly cooled to room temperature.

For each of the obtained sintered bodies, the density, bending strength at room temperature and high temperature, fracture toughness value, and thermal shock resistance (maximum temperature difference without strength deterioration due to sudden temperature change) were measured. The results are shown in Table 1.

(Left below) As is clear from Table 1, the sintered body obtained by the method of the present invention has a relative density as high as 98.5%, and a bending strength of 80 kgr/m or more at room temperature and 1300°C. and 80
It was found that it has a high thermal shock resistance of 2 kgf/m and excellent thermal shock resistance.

As described in detail, the present invention aims to inexpensively produce silicon nitride ceramics having high density, high strength, and high toughness in large quantities under normal pressure or nitrogen pressure without hot pressing. This has made it possible, and its industrial usefulness is extremely large.

Claims (3)

[Claims] 1. A silicon nitride ceramic sintered body comprising 0.1 to 10% by weight of cerium oxide, 0.1 to 10% by weight of hafnium oxide, and the balance consisting of silicon nitride. 2. A mixed powder consisting of 0.1 to 10% by weight of cerium oxide, 0.1 to 10% by weight of hafnium oxide, and the balance being silicon nitride is molded, and the molded body is heated at 1500 to 1650°C in a non-oxidizing gas atmosphere containing nitrogen. After holding for more than 1 hour,
A method for producing a silicon nitride ceramic sintered body, which comprises holding and sintering at 1700 to 1780°C for 2 hours or more. 3. A mixed powder consisting of 0.1 to 10% by weight of cerium oxide, 0.1 to 10% by weight of hafnium oxide, and the balance being silicon nitride is molded, and the molded body is heated at 1500 to 1650°C in a non-oxidizing gas atmosphere containing nitrogen. After holding for more than 1 hour,
After being maintained at 1700 to 1780°C for more than 2 hours, it was further heated to 178°C in a non-oxidizing gas atmosphere containing nitrogen at 10 atm or more.
1. A method for producing a silicon nitride ceramic sintered body, which comprises heating and sintering at 0 to 2000°C.