JPH0244070A - Production of ceramic sintered body - 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 method for manufacturing a ceramic sintered body with improved toughness.

(Prior Art) In order to improve the toughness of a ceramic sintered body, a method has been used in which ceramic powder and whiskers are mixed to form a molded body, and the molded body is sintered.

(Problem to be Solved by the Invention) However, in the above method, when mixing ceramic powder and whiskers, it is extremely difficult to uniformly disperse the whiskers because the whiskers have poor fluidity. There is a problem in that it is not possible to obtain a homogeneous ceramic sintered body.

In addition, since whiskers have high elasticity, they do not deform plastically, so when a compact is formed by mixing ceramic powder and whiskers, a dense compact cannot be obtained.As a result, the compact cannot be sintered. There is a problem that the obtained sintered body has a low density.

Also, during sintering, sintering is not performed sufficiently at the interface between the ceramic powder and the whiskers, that is, there is not much bonding due to sintering at the interface, so it is not possible to obtain a good sintered state. There is a problem in that it is not possible to improve the toughness of the body.

An object of the present invention is to solve these problems and provide a method for manufacturing a ceramic sintered body with improved toughness.

(Means for Solving the Problems) In order to achieve the above object, the present invention mixes ceramic powder and whisker-forming powder to form a compact, and heats the compact in a pressurized gas atmosphere. The method is characterized in that the whisker-forming powder is evaporated or decomposed or decomposed and evaporated to form whiskers and sinter the molded body by utilizing the difference in steam and atmospheric pressure between the reaction system and the production system.

The ceramic powder used in the present invention is not particularly limited to those with specific components, but for example, N2031
Examples include those containing at least one of SIC+ 813 N41 ZrO2 as a main component, and the particle size thereof is about 0.1 to 20 μm.

In addition, whisker-forming powders are not limited to those with specific components, but for example, SIC
, Sii N4. Tic, TIN, ZrC.

Examples include those whose main component is one or more of ZrN, MoC2, and MoN2, and the particle size is 0.1
The thickness should be approximately 20 μm.

Further, the mixing ratio of the ceramic powder and the whisker-forming powder may be appropriately selected depending on the material of the ceramic sintered body to be obtained, and is approximately 5:95 to 95:5.

In addition, when mixing ceramic powder and whisker-forming powder to form a compact, the carbon added is as follows:
For example, graphite powder, carbon.

A fired powder of an organic resin such as black, stearic acid, polyacrylamide, polyvinyl acetate, or water-soluble phenol resin may be used, and one or more of these may be added, and the amount of addition may vary depending on the amount of ceramic powder. The amount is about 0.1 to 1.0% based on the whisker-forming powder mixture.

When forming a molded body by mixing ceramic powder and whisker-forming powder, for example, y2o3゜5lo2,
Oxides such as TlO2, ZrO2, N002 may be added as sintering aids.

In addition, the gas used when heating the molded body formed by mixing the ceramic powder and the whisker-forming powder is, for example, Ar alone, A'niN2.82°NI+3, C
A mixed gas is used, which is a mixture of one or more of the following gases:
Preferably it is 55 to 95%.

The temperature and time for heating in the gas atmosphere may be appropriately selected depending on the material of the molded body, but the temperature is generally 1400°C or higher, preferably 1400°C or higher.
The temperature is 600 to 2200℃, and the time is generally 1
Color for ~5 hours.

Further, the pressure when heating the molded body in a gas atmosphere is generally about 2 to 2000 atmospheres.

Incidentally, whiskers are formed by heating a compact formed by mixing ceramic powder and whisker-forming powder in a gas atmosphere to evaporate or decompose or decompose and evaporate the whisker-forming powder. This is thought to be due to the following reasons. In other words, when heating is performed at a high temperature in a gas atmosphere, compounds with lower vapor pressure in the production system than in the reaction system are produced, as shown in the following formula (% formula %), so the compounds produced in a vapor state are removed from the system. This is because whiskers are formed by solidification and precipitation, and as a result, the reaction always proceeds from left to right.

For example, when 513N4 and 5i02 are used as whisker-forming powder, 513N4→3SI+2N...
Whiskers are formed by the reaction caused by the decomposition of (1).

In this case, the vapor pressure of SI3N4 is lower than that of SIC.

In addition, the size of the whiskers formed between the ceramic powder particles is about 10 to 2000 μm in length, and the diameter is φ0.
．． 1-1. The amount produced depends on the amount of whisker-forming powder mixed with the ceramic powder, for example, Sl and N.

In the case of , it is about 0.1 to 30% (volume ratio).

(Function) By mixing ceramic powder and whisker-forming powder to form a compact, the whisker powder is uniformly dispersed in the ceramic powder and the compact is densified.

Further, the molded body is heated in a pressurized gas atmosphere to evaporate or decompose or decompose and evaporate the whisker-forming powder to form whiskers by utilizing the difference in vapor pressure between the reaction system and the production system. By sintering the body, sintering is also promoted at the interface between the whisker and the ceramic, and the sintered body is also densified with a good sintered state.

Further, by adding carbon to the molded body, evaporation of the whisker-forming powder is promoted.

(Example) Next, specific examples of the present invention will be described together with comparative examples.

Example 1 92% silicon nitride powder with an average particle size of 0.7 μm, 4v 1% of yttrium oxide with an average particle size of 0.4 μm, 0 average particle size
．． 1.5 wt of polyvinyl acetate emulsion was added to 100 g of mixed powder consisting of 4 wt% of 4 μm aluminum oxide.
%, ammonium polyalginate 0.3 wt%, stearic acid emulsion 0.3 wt%, carbon black 0.3 wt%, water-soluble acrylic resin 0.1 vt%
were added and dispersed in 30 g of water/100 g of powder to obtain a dispersion.

Subsequently, the resulting dispersion was slip cast to a size of 50
Formed into a plate-like body of 15 x 100 mm, the plate-like body was heated in air at a temperature of 80°C for 10 hours, at a temperature of 110°C for 5 hours, at a temperature of 210°C for 5 hours, at a temperature of 360°C for 5 hours, and at a temperature of 40°C.
A molded article was prepared by successively drying at 0° C. for 10 hours.

Furthermore, the produced compact was placed in a carbon crucible and fired in a mixed gas atmosphere consisting of 10% argon gas and 90% nitrogen gas at a pressure of 300 atm and a temperature of 1700°C for 2 hours to obtain a ceramic sintered body. I got it.

The size of the obtained ceramic sintered body is 10×10×6
The sample was cut to 0 mm and wrapped with diamond to a thickness of 0.8 μm.

The appearance, shrinkage rate, and relative density of the obtained ceramic sintered body were examined, and the results shown in the table were obtained.

In addition, we investigated the bending strength, fracture toughness and hardness using the chevron notch method of samples made by cutting ceramic sintered bodies, as well as SEX observation of the fractured surface after the sample fractured, whisker crystal structure observation using X-ray diffraction, and polishing. When the surface was observed using an optical microscope, the results shown in the table were obtained.

The conditions for measuring bending strength and fracture toughness are as follows.

■ Bending strength: The three-point bending method of JIS R1601 was followed, the upper span was 10+++n, the lower span was 30, and the crosshead speed was 0.5 city/min.

■ Fracture toughness: Calculated based on the KIC calculation method in accordance with JIS R1601.

Example 2 Ceramic sintered bodies and cut samples were prepared in the same manner as in Example 1, except that instead of placing the compacts in a carbon crucible, they were embedded in silicon nitride powder to which 10 wt% of carbon black was added. Then, by the same method as in Example 1, the appearance of the ceramic sintered body was observed, the shrinkage rate, the relative density, the bending strength of the sample, the fracture toughness, the hardness, and the SE of the fracture surface after the sample was fractured.
When M observation, whisker crystal structure observation, and optical microscope observation of the polished surface were performed, the results shown in the table were obtained.

The composition of the comparative molded body was 60 νt% ceramic powder made of 81384 with an average particle diameter of 0.7 μm, and whisker 3 made of silicon carbide with an average diameter of 1.2 μm and an average length of 201 m.
0vt%, 5vt% yttrium oxide, 5wt% aluminum oxide, and sintering of the molded body using 5% argon gas.
at a temperature of 17% in a mixed gas atmosphere consisting of 95% nitrogen gas and
Ceramic sintered bodies and cut samples were prepared in the same manner as in Example 1 except that the temperature was 50° C. for 2 hours. Then, in the same manner as in Example 1, the appearance of the ceramic sintered body was observed, the shrinkage rate, the relative density, the bending strength of the sample, the fracture/toughness, the hardness, the SEM observation of the fracture surface after the sample was fractured, the whisker crystal structure observation, and the polished surface. When observed with an optical microscope, the results shown in the table were obtained.

As is clear from the table, the ceramic sintered bodies obtained by the methods of Examples 1 and 2 of the present invention had improved relative density and fracture toughness compared to the ceramic sintered bodies obtained by the conventional method of the comparative example. was confirmed.

Example 3 Ceramic sintered bodies with holes were obtained in the same manner as in Example 1, except that the amount of carbon black added to the mixed powder was varied. Then, the fracture toughness of each ceramic sintered body was examined using the same method as in Example 1. The relationship between the fracture toughness of each ceramic sintered body examined and the amount of carbon black added is shown as a curve in FIG.

As is clear from FIG. 1, it was confirmed that the ceramic sintered body obtained when the amount of carbon black added to the compact was 0.1 to 0 wt% had extremely high fracture toughness.

Example 4 Ceramic sintered bodies were obtained in the same manner as in Example 1, except that the pressure of the atmosphere when heating the molded body in a gas atmosphere was varied. Then, the growth and growth of whiskers in each ceramic sintered body was examined using the same method as in Example 1. The relationship between whisker growth and pressure for each ceramic sintered body examined is shown as a curve in FIG.

As is clear from FIG. 2, it was confirmed that the whiskers of the obtained ceramic sintered body became longer as the atmospheric pressure increased.

Example 5 A ceramic sintered body was prepared using the same method as in Example 1, except that the mixing ratio of argon gas and nitrogen gas in the gas atmosphere when heating the molded body in the gas atmosphere was varied, with each gas atmosphere having holes. I got it.

Then, the whisker formation rate of each ceramic sintered body was examined using the same method as in Example 1. The relationship between the whisker formation rate and the mixed gas atmosphere for each of the examined ceramic sintered bodies is shown as a curve in FIG.

As is clear from Figure 3, when a mixed gas is used in the gas atmosphere during heating, the amount of argon gas in the gas is 55%.
It was confirmed that the whisker formation rate was high when the concentration was ~95%.

(Effects of the Invention) According to the present invention, since the ceramic powder and the whisker-forming powder are mixed to form a compact, a dense compact in which whiskers are uniformly dispersed can be formed. In addition, the compact is heated in a pressurized gas atmosphere to evaporate or decompose or decompose and evaporate the whisker-forming powder to form whiskers using the difference in vapor pressure between the reaction system and the production system. Since the molded body is sintered, a good sintered state can be obtained at the interface between the ceramic and the whisker, making it extremely easy to produce a ceramic sintered body with high density and excellent toughness. It has advantages such as being able to be manufactured.

Furthermore, by adding carbon to the molded body, a ceramic sintered body with further improved toughness can be produced extremely easily.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the relationship between fracture toughness and carbon black content of ceramic sintered bodies in Examples of the present invention, Figure 2
The figure is a characteristic diagram showing the relationship between whisker growth and pressure in the ceramic sintered body in the example of the present invention, and Figure 3 is the relationship between the whisker formation rate and the mixed gas atmosphere in the ceramic sintered body in the example of the present invention. FIG. Outside 3 people Figure 1 111111-Carpo bluff t (Z%)--1→
Cloud group prayer pressure 77 (wono)

Claims (2)

[Claims] 1. A ceramic powder and a whisker-forming powder are mixed and formed into a molded body, and the molded body is heated in a pressurized gas atmosphere to evaporate and decompose or decompose and evaporate the whisker-forming powder to form a reaction system and a production system. 1. A method for producing a ceramic sintered body, which comprises forming whiskers and sintering the molded body by utilizing a difference in vapor pressure between the two. 2. 2. The method of manufacturing a ceramic sintered body according to claim 1, wherein the molded body is formed by further adding carbon to the ceramic powder and the whisker-forming powder.