JPS61122164A - Silicon carbide-alumina composite 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 A. Field of Industrial Application The present invention relates to a silicon carbide-alumina composite sintered body and a method for manufacturing the same. Silicon carbide with excellent thermal shock resistance
The present invention relates to an alumina composite sintered body and a method for manufacturing the same.

BACKGROUND OF THE INVENTION In recent years, silicon carbide, together with silicon nitride and a silicon-aluminum oxynitride called Sialon, has attracted attention for its potential as a material for high-temperature structures, and various applications are being considered. However, silicon carbide cannot be said to have sufficient mechanical strength and thermal shock resistance at high temperatures to provide reliability.

An example of improving mechanical strength by dispersing alumina particles as a second phase in a brittle material is described by Lange in J.
our own of American Cevami
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An example is found where the matrix is glass, as reported in 971, but this example is not intended for high temperature structural materials.

In addition, the use of alumina as a sintering aid for densification of silicon carbide sintered bodies was proposed by Lange in Jou.
rnal of Materials 8science
, 10.314-320.1975. In this study by Lange, silicon carbide powder with a particle size of 3 μm or less and alumina powder with a particle size of 0.05 μm were used, hot press conditions were set at 1950°C for 1 hour, and a pressure of 275 KP/c-i, and the alumina formulation was 2 volumes. A density higher than the theoretical density of 99 inches was obtained. The role of this alumina is interpreted to be that a liquid phase is formed at the sintering temperature, and silicon carbide is densified by dissolution and reprecipitation through this liquid phase. However, in this case, since alumina mainly exists as a grain boundary phase in a continuous network at the grain boundaries of silicon carbide, there is a problem that the mechanical strength decreases due to the softening of the alumina grain boundary phase at high temperatures of 1200°C or higher. .

As a silicon carbide sintered body whose high-temperature strength is improved by blending alumina with raw material powder, JP-A-57-42577 discloses a mixture consisting of 0.5 to 35% by weight of aluminum oxide and the remainder substantially silicon carbide. The bending strength at room temperature and 1400℃ obtained by sintering without applying pressure after molding is 2511P.
A high-density and high-strength silicon carbide ceramic sintered body having a density of /- or more has been proposed. This sintered body exhibits a fairly high bending strength at high temperatures, but the alumina is decomposed and evaporated to separate from the molded body, and this type of silicon carbide sintered body has low resistance to sudden changes in temperature. In other words, no improvement in thermal shock resistance can be expected.

C. Purpose of the Invention The present invention solves the problems of conventional silicon carbide sintered bodies as described above, and provides a silicon carbide sintered body that has excellent mechanical strength and thermal shock resistance at high temperatures, and its production. The purpose is to provide a method.

2. Structure of the invention, that is, the first aspect of the present invention is that alumina particles with an average particle size of 2 to 25 μm are substantially separated from each other in a matrix consisting essentially of silicon carbide particles with an average particle size of 1 μm or less. The present invention relates to a silicon carbide-alumina composite sintered body having a structure dispersed in 3 to 30 volumes and having excellent mechanical strength and thermal shock resistance at high temperatures.

The second invention of the present invention is to blend and mix alumina powder with an average particle size of 2 to 25 μm to silicon carbide powder with an average particle size of 1 μm or less so that the total volume is 3 to 30 μm, and this mixture The silicon carbide-alumina composite sintering according to the first invention, characterized in that the powder is solid-phase sintered by hot pressing at a molding temperature within the range of 1900 to 2000°C and a molding pressure of 100 m1P/cIit or more. It pertains to a method for producing a solid.

First, the configuration of the first invention will be explained.

The first invention aims to improve mechanical strength and thermal shock resistance, particularly at temperatures of 1200° C. or higher, by dispersing alumina particles in a silicon carbide matrix.

Regarding mechanical strength at high temperatures, the condition of grain boundaries between silicon carbide particles constituting the matrix is important.

In the present invention, m) silicon carbide particles having an average particle size of 2 to 5 μm, which is sufficiently larger than the silicon carbide particles having an average particle size of 1 μm or less (particularly preferably 0.1 to 0.5 μm) constituting IJ Fuchs;
of alumina particles are dispersed in the matrix and sintered at a temperature within the range of 1900 to 2000°C below the melting point of alumina (2050°C). Its microscopic structure is completely different from that of a sintered body produced by liquid phase sintering and hot pressing, which is used as an agent.

The sintered body according to the present invention has a microscopic structure in which alumina grain phases are independently dispersed one by one in a silicon carbide matrix with almost no alumina grain boundary phase at the grain boundaries, and the above-mentioned alumina Due to silicon carbide, in which the main grain boundary phase exists in the form of a network, the dispersed alumina particles soften at high temperatures of 1000°C or higher, reducing the degree of interaction between the alumina particles and the crack tips that lead to fracture. It is thought that this interaction becomes larger than that at room temperature, and as a result, the fracture toughness increases at high temperatures and the mechanical strength at high temperatures is improved.

Regarding thermal shock resistance, the mechanical condition of the interface between the alumina particles and the silicon carbide matrix is important.

Thermal shock resistance was determined by CeramicE by Lewis et al.
ngineering 5science Procee
ding 1, 634-643, 1982, there are two expression methods, one of which is the resistance to the occurrence of cracks under thermal stress (thermal shock fracture resistance), and the other is the resistance to the occurrence of cracks under thermal stress. It is expressed as the ratio of mechanical strength before and after thermal shock (thermal shock damage resistance) when cracking is unavoidable.

The former is The latter is σi　　σi2 It can be written as

Here, jTc is a critical temperature difference that causes a decrease in mechanical strength by quenching in water from a high temperature difference ΔT with water, and is a value indicating resistance to crack generation, σ
t is mechanical strength before thermal shock, σr is ΔT>jT
The retained mechanical strength after being subjected to a thermal shock, E
is Young's modulus, V is Poisson's ratio, α is linear expansion coefficient, rrc
is the effective fracture energy, k is the thermal conductivity, h is the heat transfer coefficient of the surface during quenching, b is the characteristic length related to the sample size, and N is the density of the number of cracks generated by thermal stress.

When the above equation (2) is rewritten using the basic equation of fracture mechanics described in "Mechanical Properties of Ceramics" K edited by Ceramics Association, it becomes as follows.

Here, a is the length of the crack that leads to fracture, and y is a constant related to the geometry of the crack.

From the above formulas (1) and (2)/, the thermal shock rupture resistance is:
High initial mechanical strength σi, Young's modulus E and linear expansion coefficient α
It is believed that by lowering the thermal shock damage resistance, the thermal shock damage resistance is increased by increasing the density of the number of cracks generated by thermal stress, respectively.

As a result of intensive research, the inventors & Jin discovered that by independently dispersing alumina particles with an average particle size of 2 to 25 μm in a silicon carbide matrix as a second phase, carbonization with the alumina particles in the sintered body was achieved. It has been found that both thermal shock fracture resistance and thermal shock damage resistance can be improved by providing cracks or residual stress that facilitates the generation of cracks at the interface with the silicon matrix.

That is, regarding thermal shock fracture resistance, the presence of independent fine racks at the interface between the alumina particles and the silicon carbide matrix mainly reduces the Young's modulus E without reducing the initial mechanical strength in equation (1) above. Thermal shock breakdown resistance ΔTc is improved.

Regarding thermal shock damage resistance, if there is a crack at the interface between the dispersed alumina particles and the silicon carbide matrix, energy will be absorbed by crack branching at the interface during the propagation of the crack generated by thermal shock. In addition, when there is residual stress (home), cracks preferentially occur at the above interface under thermal shock, due to the generation of numerous fine cracks corresponding to the alumina particles.
That is, by increasing N in formula (2) 7, the thermal shock damage resistance is improved.

The above cracks or residual stress occur at the interface between the alumina particles and the silicon carbide matrix due to the difference between the coefficient of thermal expansion of alumina and that of silicon carbide. The former is larger than the latter. In addition, when a reaction product is formed between the alumina particles and the silicon carbide matrix, the above interface is the interface between the alumina particles and the reaction product, the reaction product itself, and the interface between the reaction product and the silicon carbide matrix. It includes both.

Next, each phase constituting the sintered body will be described. Silicon carbide that constitutes the matrix has crystal forms of α type and β type, and many similar types of α type have been discovered. The sintered body based on the present invention has a temperature of 1900 to 2000, as described below.
Since it is sintered at a relatively low temperature of °C, no β-α transformation occurs, and any crystal form may be used. The average particle diameter is preferably 1 μm or less, particularly preferably 0.1 to 0.5 μm. The average particle size of the silicon carbide particles needs to be smaller than the average particle size of the alumina particles dispersed in the matrix and have an appropriate balance with this, and as described later, the lower limit of the average particle size of the alumina particles must be Since it is 2 μm, the upper limit of the average particle size of silicon carbide particles is 1 μm. When this becomes larger than 1 μm, the overall level of mechanical strength at room temperature and high temperature becomes low.

The alumina particles to be dispersed in the matrix may be of α type crystal form, but may also be of other crystal form. Moreover, the shape may be equiaxed, but it may also be plate-shaped. However, in the case of plate-shaped alumina particles,
It is preferable that the aspect ratio is on average less than m.If the aspect ratio exceeds the average, the alumina particles become entangled with each other and cannot be dispersed independently, resulting in a decrease in mechanical strength at room temperature and high temperature. Become.

The average particle size of the alumina particles needs to be sufficiently larger than that of the silicon carbide particles constituting the matrix,
The thickness is 2 to 25 μm. If this is less than 2 μm, 19
At a sintering temperature of 00 to 2000°C, it is easy to react with the pure substances contained in the non-silicon carbide particles to form a liquid phase compound, and it is difficult to obtain a structure in which alumina particles are dispersed independently of each other9. On the other hand, if the thickness exceeds 6 μm and becomes coarse, stress concentration becomes large.9 In either case, the mechanical strength at room temperature and high temperature decreases.

The proportion of alumina particles in the matrix is 3 to 3
Let the volume be 0. If it is less than 3 volumes, the sintered body will not be sufficiently dense and its mechanical strength will decrease, and if it exceeds the blade volume, there will be parts where the alumina particles come into contact with each other. The alumina particles form a continuous network, reducing mechanical strength at high temperatures.

When the alumina particles are plate-shaped, it is desirable to keep the upper limit of the amount of dispersion as low as possible.

Although the sintered body according to the present invention is composed of two types of components, silicon carbide and alumina, there is no problem even if small amounts of other components contained as impurities in the raw materials are present.

Next, the configuration of the second invention will be explained.

It goes without saying that the average particle diameters of the silicon carbide powder and alumina powder particles used as the raw material powder are the same as those in the first invention.

The purity of silicon carbide powder is preferably 95% or more, more preferably 98% or more, and the purity of alumina powder is preferably 98% or more.

Note that instead of alumina powder, it is also possible to use powder of aluminum salt, such as aluminum hydroxide or aluminum sulfate, which converts into alumina.

The raw material powders are preferably mixed using an inert mixed liquid in an inert ball mill using inert balls.

Molding and sintering are performed using a graphite mold in a non-oxidizing atmosphere.
Temperature 1900-2000℃, molding pressure 100KP/cI/
This is done using a hot press.

If the hot press temperature is lower than 1,900°C, the density of the resulting sintered body will decrease, and if it exceeds 2,000°C, the entire alumina powder or a part of the alumina powder will melt, forming a network-like grain boundary mainly composed of alumina. Phases begin to form, and in both cases the mechanical strength at room and high temperatures decreases.

If the molding pressure is less than 10011 /st, the density of the obtained sintered body will not be sufficiently high, so the molding pressure is set to 100 b/aA or more.

E, Example Hereinafter, specific examples of the present invention will be described.

Beta-type silicon carbide powder with a purity of 98% or more and an average particle size of 0.3 μm is mixed with alumina powder as shown in the table below, and ethyl alcohol is mixed as a mixed liquid in a ball mill using a plastic container and an alumina ball. The mixture was wet mixed for a period of time and dried to form a mixed powder.

These mixed powders are processed using a graphite mold in a nitrogen gas stream.
Temperature 1950℃, molding pressure 280 KP/art? The material was hot-pressed for 1 hour to obtain a disc-shaped sintered body with a diameter of 501 μL and a thickness of 5.5 μL.

From these sintered bodies, a 3X4X38 specimen was collected using a diamond grindstone and a diamond blade.
A test piece was finished with a No. 200 diamond abrasive grindstone and subjected to density measurement, bending test, and thermal shock test.

The bending test was performed using an outer fulcrum distance of 30 fi and an inner fulcrum distance of 10 fi.
B. It was carried out at room temperature and 1400° C. by the method of 4-point bending test with a crosshead speed of 0.5 m/m.

In the thermal shock test, the test piece is suspended in an atmospheric furnace and a predetermined ΔT is applied.
The temperature was raised to a temperature that gave , held for 10 minutes, and then quenched in water to give a thermal shock.The bending strength was measured by the above bending test method, and the -41 strength diagram was determined to obtain ΔTc and -.

σ The test results are as shown in Table 1 below.

(See margin below, go to next page) Typical ceramic structures of the sintered bodies in Table 1 are shown in the drawings as micrographs at 200x magnification, taking /fL6 as an example.

The drawing shows a matrix consisting of fine silicon carbide particles.
It is observed that the alumina particles 2 are separated from each other and dispersed independently.

For comparison, the above table also shows the results of a similar test in which 2 volumes of equiaxed alumina powder with an average particle size of 0.05 μm were mixed.

From the table, the silicon carbide-alumina composite sintered body based on the present invention has significantly improved bending strength and thermal shock resistance at high temperatures compared to the conventional silicon carbide sintered body using alumina as a sintering aid. I understand that there is.

Therefore, it can be said that the sintered body based on the present invention has a high possibility of being applied to various uses as a high-temperature structural material such as gas turbine parts.

In the detailed description of the invention, the first aspect of the present invention is that the matrix consists essentially of silicon carbide particles with an average particle size of 2 to 25 μm, and the alumina particles with an average particle size of 2 to 25 μm are substantially formed in the matrix. Because it is a silicon carbide-alumina composite sintered body with a structure that is separated from each other and dispersed in 3 to 30 volumes, it has extremely excellent mechanical strength and thermal shock resistance at high temperatures, making it highly suitable as a material for high-temperature structures. It can be used to express reliability.

Further, the second aspect of the present invention is to blend and mix alumina powder with an average particle size of 2 to 25 μm to silicon carbide powder with an average particle size of 1 μm or less so that the total volume is 3 to 30 μm. , a silicon carbide-alumina composite sintered body, characterized in that this mixed powder is hot-pressed and solid-phase sintered at a molding temperature within the range of 1900 to 2000°C and a molding pressure of 100 Ff/cd or more. Since this is a manufacturing method, the silicon carbide-alumina composite sintered body having excellent high-temperature mechanical strength and thermal shock resistance based on the first invention can be easily manufactured without requiring special equipment. can.

[Brief explanation of the drawing]

The drawing is a micrograph at a magnification of 200 times showing the ceramic structure of the silicon carbide-alumina composite sintered body according to the present invention. In addition, in the symbols shown in the drawings, l-φ: silicon carbide matrix 2: alumina particles.

Claims (1)

[Scope of Claims] 1. Alumina particles having an average particle size of 2 to 25 μm are substantially separated from each other and dispersed in a volume % of 3 to 30% in a matrix consisting essentially of silicon carbide particles having an average particle size of 1 μm or less. A silicon carbide-alumina composite sintered body having a microstructure and excellent mechanical strength and thermal shock resistance at high temperatures. 2 Silicon carbide powder with an average particle size of 1 μm or less has an average particle size of 2~
25μm alumina powder 3-30% by volume of the whole
Blend and mix this mixed powder so that it becomes
Temperature within the range of 900-2000℃, molding pressure 100Kg
A method for producing a silicon carbide-alumina composite sintered body having excellent mechanical strength and thermal shock resistance at high temperatures, the method comprising hot pressing at a pressure of /cm^2 or higher and solid-phase sintering.