JPH0319191B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a method for manufacturing composite ceramics,
In particular, it relates to a method for producing structural composite ceramics that require high toughness and high-temperature strength. [Background of the Invention] In general, engineering ceramics suitable for structural materials such as engines and turbines include:
Nitrogen silicon, silicon carbide, and the like are known to have excellent heat resistance and thermal shock resistance. However, since silicon nitrogen and silicon carbide are compounds with strong covalent bonds, it is difficult to sinter them alone, and it is necessary to add a sintering aid to obtain a high-density sintered body. For example, boron, boron compounds, aluminum, aluminum compounds, and the like are known as sintering aids when silicon carbide is sintered by hot pressing. Furthermore, when silicon carbide is sintered under normal pressure, it is known that a high-density sintered body can be obtained by adding carbon. However, in the case of the pressureless sintering method, silicon carbide easily decomposes, so that the molded body is not sufficiently densified, which is a problem especially in the case of products with complex shapes or large dimensions. Furthermore, since the glass phase created by these sintering aids softens at high temperatures, the strength of the sintered body at high temperatures decreases significantly. In order to prevent this decrease in strength at high temperatures, efforts are being made to reduce the amount of sintering aid added and to crystallize the glass at the grain boundaries caused by the sintering aid. No solution has been reached. On the other hand, apart from sintering aids, a fiber reinforcement method is also being considered that increases high-temperature strength by combining high-strength fibers (whiskers) such as SiC and silicon nitride (Journal of Ceramics Association, 91, [ 11], 1983,
P491). The reason this method is effective is (1): Whiskers stop or suppress the expansion of minute scratches in ceramics, preventing stress concentration. (2): Whiskers strongly bond with ceramics,
Whiskers carry stress. (3): If the whiskers are weakly bonded (for example, physically attached) to the ceramics, energy absorption occurs due to the pulling of the fibers from the ceramics. (4): Whiskers break in sequence starting from the weakest part, so the fracture surface becomes complex. It is believed that the above effects improve the brittleness and thermal shock resistance of ceramics. However, in the production of such fiber-reinforced ceramics, there is a problem in that the whiskers become entangled with each other during mixing of raw materials, resulting in lumps. Therefore, as a method for dispersing whiskers in a matrix, the whiskers are placed in water, dispersed by mechanical stirring or ultrasonic irradiation, passed through a filter to remove undispersed lumps and granules, and then suctioned. , it is being considered to use it as a green sheet. However, since this is a two-dimensional composition, anisotropy is likely to occur. Therefore,
In order to obtain a high-strength, high-toughness composite sintered body using whiskers, it is a big problem to properly disperse them three-dimensionally. [Object of the Invention] An object of the present invention is to provide a method for manufacturing composite ceramics in which ceramic particles are bonded with whiskers in order to obtain high toughness and high-temperature strength. [Summary of the Invention] The present invention achieves high toughness and high-temperature strength by bonding particles together and reducing voids between particles using whiskers generated from metal Si powder in a compact during firing. be. A feature of the manufacturing method of the composite ceramics of the present invention is that a molded body of a mixture mainly containing at least one of inorganic compounds such as oxides, carbides, nitrides, and oxynitrides and metal Si is prepared with an oxygen concentration of 10 ppm or less. The fired product is heated in nitrogen gas at a temperature of 1100 to 1400°C, which is below the melting point of metal Si, to form a sintered body with a diameter of 0.1 μm to 2 μm and a length of 5 μm between the particles.
The following method involves growing needle-like whiskers and bonding particles together using the whiskers. In the present invention, the reason why the particles of the molded body are bonded to each other by whiskers generated during firing of the molded body is that if the whiskers are mixed and dispersed in the raw materials in advance, the whiskers will be bonded between the particles in the fired body. Although present in the voids, not all whiskers are combined with particles, and some whiskers remain in the form of lumps or exist alone. According to the present invention, the voids between particles are bonded by a large number of needle-shaped whiskers generated from particles in the molded body extending relatively straight and intersecting, and there is no whisker that is not in a bonded state. It provides toughness and high-temperature strength. FIG. 1 shows the bonding state of whiskers produced in a sintered body according to the present invention. Further, FIG. 2 shows the bonding state of whiskers in a sintered body when whiskers are mixed and dispersed in the raw materials in advance. In the present invention, the reason why whiskers are generated in the compact by heating and growing at a temperature below the melting point of metal Si in nitrogen gas with an oxygen concentration of 10 ppm or less is that whiskers do not form on the surface of the compact in nitrogen gas with an oxygen concentration of over 10 ppm. This is because whiskers are generated. Also, metal Si
When heated to a temperature above the melting point of the metal, Si melts and oozes out to the surface, and most of the generated whiskers scatter to the outside of the sintered body, and the effect of generating nitrogen silicon whiskers from Si inside the sintered body is small. It is from. Therefore, by heating under the heating conditions of the present invention for an appropriate time depending on the size of the molded product, more whiskers can be generated in the molded product. In addition, in the present invention, for 100 parts by weight of fired particles,
It is preferred that whiskers are contained in an amount of 1 to 70 parts by weight, preferably 10 to 30 parts by weight. The reason for this is that when the whisker contains 10 parts by weight to 70 parts by weight, there is almost no change in toughness, and if the whisker is less than 1 part by weight or more than 71 parts by weight, no more remarkable effect than before can be seen. Furthermore, in the present invention, the heating temperature for firing is
The temperature is preferably 1100 to 1400°C. [Embodiments of the Invention] Example 1 A mixed powder of 50 g of silicon carbide with an average particle size of 16 μm and 21 to 80 g of metallic silicon with an average particle size of 1 μm to generate nitrogen silicon whiskers, and 10% polyvinyl butyral as a forming aid. Add 100 c.c. of solution,
The mixture was mixed in a pot mill for 24 hours, and then dried at room temperature to provide a test material. These raw materials were molded using a mechanical press at a molding pressure of 250 kg/ ^cm2 , each having a diameter of
It was molded into a 50mm and 30mm thick piece. After dispersing and volatilizing the molding aid from each molded body, the oxygen concentration
10 hours at 1100℃ in 3ppm nitrogen gas, then
1200℃ for 20 hours, then 1300℃ for 10 hours, then
After being maintained at 1350°C for 5 hours or more, it was cooled in a furnace. Here, each temperature increase rate is 10°C/min. Table 1 shows the test results of the obtained sintered body. The fracture toughness value (K _IC ) was measured by the notched beam method using a diamond wheel to make a 0.5 mm notch in a 3 x 4 x 40 mm (span of three-point bending test: 30 mm) test piece. For comparison, Table 2 No. 1 shows samples that were similarly heat-treated in nitrogen gas with an oxygen concentration of 30 ppm. In addition, silicon nitride whiskers are mixed and dispersed in the raw material from the beginning as in the past, and heat-treated products are shown in Table 2 No. 2.
Shown below.

【table】

[Table] Fracture surfaces of sintered bodies according to examples of the present invention after testing
When observed with a SEM, acicular and fibrous silicon nitrogen whiskers with a diameter of 0.1 to 2 μmφ and a length of about 5 μm extend almost linearly into the voids between silicon carbide particles.
It was found that they intersect and connect dimensionally. Comparative Example No. 1 in Table 2, which was heat-treated in nitrogen gas with a high oxygen concentration, hardly any silicon nitride whiskers were formed in the sintered body, and white silicon nitride whiskers were formed on the surface of the sintered body. However, the relative density of the sintered body was only about 70%. In the case of the mixed whisker No. 2 in Comparative Example Table 2,
Many lumpy silicon nitride whiskers were observed, and it was found that the voids between particles were not completely bonded. Example 2 50 g of titanium nitride with an average particle size of 2 μm and an average particle size of 1 μm
m mixed powder of 50g of metal silicon, average particle size 1μ
Mixed powder of 50g of alumina of m, average particle size of 1μm and metal silicon 50g, Si-Al-O with average particle size of 1μm
Table 3 shows the test results of a sintered body in which 50 g of -N mixed powder was mixed, molded, and heated in the same manner as in Example 1.

[Table] When the fracture surface of the sintered body was observed with a SEM after the test, it was found that, as in Example 1, the voids between the particles were 0.1 to 2μ in diameter.
It was found that needle-like and fibrous silicon nitride whiskers with mφ length of about 5 μm extend almost linearly and are intersected and bonded three-dimensionally. Example 3 50 g of silicon nitride with an average particle size of 5 μm, 33 to 95 g of metal silicon with an average particle size of 1 μm to generate silicon nitride whiskers, and 5 g of magnesium oxide as a sintering aid were added and mixed in a pot mill for 24 hours. It was used as a test raw material. These raw materials were molded using a mechanical press at a pressure of 500 kg/cm ² to a diameter of 100 mm.
A piece with a thickness of 30 mm was molded. This is the oxygen concentration
The treatment was carried out for several hours at 1400°C or lower in a 3ppm nitrogen gas atmosphere. The temperature and time of this treatment varied depending on the amount of whiskers produced from the raw materials, but it was carried out at 1300°C for 10 hours, then at 1400°C for 5 hours or more. This primary sintered body was heated at 1750℃ in a nitrogen gas atmosphere of 1Kg/ ^cm2 .
The temperature was raised to 1 and held for 1 hour to perform densification and sintering. The test results of the obtained sintered body are shown in Table 4, Nos. 1 to 6.
Shown below. The fracture toughness value (K _IC ) was measured by the notched beam method using a diamond wheel to make a 0.5 mm notch in a 3 x 4 x 40 mm (span of three-point bending test: 30 mm) test piece. For comparison, Table 5 No. 1 shows a sample in which silicon nitride whiskers were mixed and dispersed in the raw material instead of metal silicon and heat-treated in the same manner. In addition, for another comparison, a mixed powder of silicon nitride, metallic silicon, and magnesium oxide was heat-treated for whisker growth at 1450°C for 2 ^hours in a nitrogen gas atmosphere, and then molded into a predetermined shape. Table 5 shows the temperature raised to 1750℃ in a nitrogen gas atmosphere and held for 1 hour.
Shown in No.2.

【table】

〔Effect of the invention〕

In the present invention, the toughness of the ceramic is improved because the particles are three-dimensionally bonded to each other by relatively straight whiskers. This results in
The scope of use of ceramics will expand to include refractories that require high-temperature strength, heat resistance, thermal shock resistance, and high toughness, and structural parts such as engines and turbines, as well as fields such as aviation, space-related, steel, and offshore development. .

[Brief explanation of the drawing]

The drawings schematically show the differences in whisker bonding between the present invention and a comparative example, and FIG. 1 is a schematic enlarged view of the ceramics according to the present invention, and FIG. 2 is a schematic enlarged view of the comparative example. . 1... Raw material inorganic compound particles, 2... Silicon nitride particles generated from Si, 3... Silicon nitride whiskers.

Claims (1)

[Claims] 1. A molded body of a mixture mainly containing at least one of inorganic compounds such as oxides, carbides, nitrides, and oxynitrides and metal Si is placed in nitrogen gas with an oxygen concentration of 10 ppm or less. 1100, which is less than the melting point of metal Si.
The diameter between the fired body particles is heated at a temperature of ~1400℃.
A method for producing composite ceramics, which comprises growing acicular whiskers of 0.1 μm to 2 μm and 5 μm or less in length, and bonding particles together using the whiskers. 2. The method for producing a composite ceramic according to claim 1, wherein the whisker is contained in 1 to 70 parts by weight based on 100 parts by weight of the fired particles. 3. Claims 1 or 2, wherein the sintered body obtained by the heating in the nitrogen gas is further heated and held in a nitrogen gas atmosphere to sinter it for densification.
A method for producing composite ceramics as described in Section 1.