JP3085525B2 - Whisker composite ceramics and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a whisker composite ceramic. More specifically, the present invention relates to a method for producing a whisker composite ceramic having a high fracture toughness in which whiskers are dispersed while maintaining the strength and function of the matrix in ceramics having an arbitrary size and shape. The whisker composite ceramics obtained by this technique is effective for, for example, a burner diffuser for thermal power generation, a molten metal transport pipe for the metal industry, a heat dissipation substrate for a power device, a ceramic rolling roll, a cutting tool, a wear-resistant tool, and the like.

[0002]

2. Description of the Related Art With the recent remarkable improvement in the properties, such as functionality, strength and toughness, of ceramic materials, there is a tendency to use ceramics in more various aspects. In accordance with such demands, there is a need for a technology for safely and inexpensively producing highly reliable, high-strength, high-performance, and high-toughness ceramics.

[0003] As one of means for increasing the fracture toughness of ceramics, whiskers are dispersed in a matrix. For example, silicon nitride is 1000
It is known as a material which exhibits high strength even at high temperatures exceeding ℃, is lightweight, and has excellent corrosion resistance, wear resistance and thermal shock resistance. Whisker-dispersed ceramics in which whiskers are dispersed in such a silicon nitride matrix are superior to monolithic ceramics in terms of toughness, hardness, and wear characteristics. The Journal of the Ceramic Society of Japan, 94 (1986), 55-59. Page.

[0004] Whisker-dispersed ceramics are usually produced by mixing whiskers with ceramic powder, molding and sintering (Japanese Patent Application Laid-Open No. 3-205378,
JP-A-1-203260, JP-A-60-2008
No. 63 gazette). Also, a method of laminating and sintering a plurality of green sheets obtained by sheeting a slurry containing ceramic powder and whisker with a doctor blade (JP-A-3-290368), or forming the slurry by slip casting and sintering There is also a way to do it.

[0005]

In order to produce such a whisker composite ceramic, generally, a whisker is mixed with a ceramic powder and the formed body is sintered. A sintered body obtained by using a ceramic powder in which whiskers obtained as described above are uniformly dispersed as starting materials generally has higher toughness than monolithic ceramics, but has lower strength. In addition, the orientation of the whiskers during powder molding causes directionality in the strength characteristics of the sintered body, and the whisker and the matrix material or the grain boundary glass layer react during sintering and are firmly bonded. Pull-out effect may not be sufficiently exhibited. Furthermore,
When whisker is used as a raw material powder, there is a concern that the worker who directly handles the whisker may be adversely affected.

An object of the present invention, the whiskers dispersed without impairing the strength and function of data trix is to provide a manufacturing operation method whisker composite ceramics with improved fracture toughness.

[0007]

As described above, in the whisker composite ceramics manufactured by the conventional method, it is difficult to maintain the strength and function of the matrix and to avoid the worker from directly handling the whiskers. there were. The present inventors have conducted intensive studies on means for improving toughness without impairing the strength of the matrix, and as a result, have reached the present invention.

[0008] The above problem is solved by a whisker composite ceramic in which whiskers are dispersed in the ceramic and the physical properties of the whisker in the matrix, such as the distribution density, diameter, and length, are changed in the inner direction of the matrix. You.

For example, in the case of structural ceramics, as shown in FIG. 1, a whisker distribution density of a portion responsible for strength is set to 0 or a very small amount, as in a whisker composite ceramic in which whiskers 2 are dispersed in matrix particles 1. This means that the part responsible for toughness is compounded with whiskers. Here, 3 is a pore. The whisker distribution density is changed so that it is 5 to 50% by volume at the outermost surface of the ceramic and 0 to 30% by volume at the center.

[0010] In addition, if the properties relating to the formation of whiskers are utilized, the above ceramics can be obtained by utilizing the reaction in the sintering process of the raw material powder without using whiskers as the starting material. This is achieved by mixing the matrix particles 1 and the whisker raw powder 4 as shown in FIG. 2 and causing the dispersed whisker raw powder to react in the sintering process of the filled body to generate whiskers in the ceramics as shown in FIG. In such a whisker composite ceramics manufacturing method,
It can be realized by controlling the initial relative density. Here, by adjusting the molding pressure at the time of molding, the amount of the pores 3 in FIG. 2 is adjusted, and the initial density of the mixed powder compact is controlled.

This is based on the fact that generally, the lower the initial relative density, the larger the amount of whiskers generated inside the filler, and the higher the initial relative density, the less whiskers are generated inside the compact. If the initial relative density of the powder filling is less than 20%, handling becomes difficult, and if it is more than 60%, whiskers are less likely to be generated inside. Therefore, the initial relative density of the above-mentioned powder filling is controlled to a value of 20% or more and 60% or less. As another method of lowering the initial relative density, the mixed powder may be filled in a graphite container having a desired shape, or may be formed by a slip casting method using a slurry in which the concentration of the mixed powder is adjusted. The initial relative density can also be controlled by adjusting the particle size distribution of the starting materials.

The dispersed whisker raw material powder is SiC or Si ₃ N ₄ whisker, and the raw material powder is Si ₃ N ₄ , S
One or more selected from iO ₂ , C, and polycarbosilane. In order to increase the oxygen content of the polycarbosilane, a floating polycarbosilane that has been previously heat-treated at 300 ° C. to 1000 ° C. in air may be used. The raw material powder of AlN whiskers is Al ₂ O ₃ . If SiC whiskers are formed during sintering of the filler, Ar, C
Sintering is performed in one or more atmospheres selected from O, CO ₂ , CH ₄ , and H ₂ or in a vacuum. Si ₃ N ₄ or A
In the case of 1N whisker, one selected from Ar, N ₂ and H ₂
Sinter in more than one atmosphere or vacuum.

When the initial relative density of the filler is low, the relative density of the sintered body is also low, so that the mechanical properties of the sintered body may be reduced. In such a case, the molten metal is impregnated. Alternatively, a powder that expands in volume due to a reaction with an atmospheric gas is mixed in advance. It can be avoided by such a method, and does not impair the effects of the present invention.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be further described with reference to examples.

Example 1 The relationship between the initial relative density of a mixed powder packing of a matrix powder and a whisker raw material and the amount of whiskers formed inside was examined. 10mass with Si ₃ N ₄ as matrix particles
s% carbon black added sample SN1 and Si
C as matrix particles and 10 mass% Si
Using ₃ N ₄ and 10 mass% carbon black sample SC1 was added, to prepare a powder packing. By changing the molding pressure, a packed body having a diameter of 15 mm and a relative density of 20 to 80% was prepared for each sample, and the pressure was changed to 0.1 MPa.
In Ar at 1600 ° C. for 2 hours. FIG. 3 shows the relationship between the average amount of whiskers generated inside each sample after the heat treatment and the initial relative density of the filler.

When the initial relative density is about 30% or less, whiskers are formed in the entire region from the surface of the filler to the center, and the distribution density tends to decrease from the surface toward the center. When the initial relative density was 30% to 60%, whiskers were formed near the surface of the filler but not in the center in some cases. Therefore, it was found that the whisker distribution density can be controlled by controlling the initial relative density of the filler.

Embodiment 2

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

Carbon black and Si ₃ N ₄ are added to SiC powder.
And polycarbosilane at a weight ratio shown in Table 1.
The starting material was mixed with PVB and diethylene glycol in an amount of 5 mass% each to improve moldability.
The mixture was mixed with ethanol and SiC balls in a polyethylene pot for 48 h. After drying this, 200mes
h or less, molded while controlling the relative density as shown in column (a) of Table 2, degreased, and then 0.1 MPa Ar
1400 for samples SC1 and SC2 in atmosphere
The samples SN1 and SN2 were heat-treated at 1600 ° C for 2 hours, and SiC whiskers were generated in-situ. Here, as for the sample having a relative density of 20% or less, the sample was a mixed powder filled in a cylindrical graphite container. Here, it was practically impossible to prepare a sample having a relative density of 20% or less.

The sample in which SiC whiskers are formed is heated to 1500 ° C. in a vacuum, impregnated with molten Si, and reacted with residual carbon to obtain SiC whisker-dispersed SiC whiskers.
Was prepared. The relative density of each sample after impregnation with molten Si is shown in column (b) of Table 2, and the distribution density of SiC whiskers near and at the center of the sample surface is shown in column (c). The whisker distribution density was calculated based on the image of the polished surface of the sample by a scanning electron microscope. Regarding any of the samples in which whiskers were generated in-situ, the amount of whiskers generated at the center of the sample was smaller than that near the surface, and tended to be thinner and shorter. In particular, the tendency was remarkable for the samples SN1 and SN2.

No whiskers were formed inside the sample where the initial relative density exceeded about 60%, and the whisker composite ceramic of the present invention was not obtained. When the initial relative density is 20% or less, handling of the sample after the heat treatment is extremely difficult, and Si impregnation cannot be performed.
Evaluation of mechanical properties could not be performed. Samples not corresponding to the whisker composite ceramics of the present invention are indicated by hatching in Table 2.

As a comparative material, SiC powder or a mixture of SiC powder, SiC whisker and carbon black at the compounding ratio shown in Table 1, PVB and diethylene glycol added at 5 mass% each and mixed and dried were used. It is molded to a relative density of 65%, and the molded body after the degreasing treatment is heated to 1500 ° C. in vacuum to impregnate the molten Si,
By reacting with carbon black, comparative materials 1 and 2 were obtained, respectively. Comparative material 1 is a monolithic SiC ceramic, and Comparative material 2 is a SiC ceramic in which 20% by volume of SiC whiskers are uniformly dispersed.

Each sample having undergone the Si impregnation step is 4 mm, 3 m
After polishing to dimensions of 40 mm and JIS R160,
The bending toughness and the fracture toughness were measured by the indentation microfracture method at 1 under a load of 30 kgf. The obtained results are shown in columns (d) and (e) of Table 2.

FIG. 4 summarizes the flexural strength and fracture toughness of the sample and comparative material corresponding to the present invention in Table 2. The abscissa indicates each sample number, where ● indicates bending strength and indicates fracture toughness. Although the transverse rupture strength of the comparative material 1 is high, the fracture toughness is low, and the opposite tendency is observed for the comparative material 2. On the other hand, the transverse rupture strength of the sample corresponding to the present invention is equivalent to that of the comparative material 1, and the fracture toughness is significantly improved. Whisker distribution density according to the present invention is 5 to 50% by volume at the outermost surface of the ceramic and 0 to 30% by volume at the center. It is confirmed that both the transverse rupture strength and the fracture toughness of the whisker composite ceramic are compatible. .

EXAMPLE 3 Si ₃ N ₄ , SiO ₂ , C,
Polycarbosilane and Al ₂ O ₃ were added to the matrix powder, and each mixed powder was filled with Ar, N ₂ , CO, CO ₂ , CH
_4. Heat treatment was performed in various atmospheres of H ₂ to clarify the formation of whiskers. SiC was used as a matrix material, and 10 g of a mixed powder of SiC powder and various whisker raw material powders was filled in a cylindrical graphite container having an inner diameter of 30 mm to obtain a filled sample. Each filled sample was heat-treated in various atmosphere gases, and the state of whisker formation was observed based on the image of the sample fracture surface with a scanning electron microscope. The atmosphere pressure was set to 0.1 MPa and the heat treatment time was set to 2 hours.

Table 3 summarizes the relationship among whisker raw materials, atmospheric gases, and generated whiskers. The chemical formulas in the table represent the generated whiskers, は indicates that whiskers having good shape and quantity were generated, △ indicates that whiskers were generated but the distribution was uneven, and × indicates that whiskers were not generated. . (
The values in parentheses indicate the heat treatment temperature, which is the temperature at which whisker is most likely to be generated with respect to the mixed powder.
According to the present embodiment, whisker raw materials corresponding to dispersed whiskers,
The heat treatment temperature and atmosphere conditions were obtained.

Example 4 PVB and diethylene glycol were mixed at 5 mass% each in Sample SN1 prepared at the weight ratio shown in Table 1, mixed with ethanol and SiC balls for 48 hours in a polyethylene pot, dried and sized. Using the powder, a slurry was prepared by mixing the mixed powder and water at a volume ratio of 30:70. The slurry was filled in a graphite container, sent to a freeze-drying furnace as it was, and frozen to remove water as a binder and then removed. As a result, a mixed powder filling without cracks due to drying shrinkage was obtained.

The filler was heat-treated together with the graphite container in an atmosphere of 0.1 MPa Ar at 1600 ° C. for 2 hours to generate SiC whiskers in-situ inside the filler.
The sample in which the SiC whiskers were formed was heated to 1500 ° C. in a vacuum in the same manner as in Example 1 to impregnate the molten Si and react with the residual carbon, thereby producing SiC whisker-dispersed SiC.

From these results, it was found that S powder was embedded in the mixed powder filling of an arbitrary shape obtained by the injection molding method using a water binder.
iC whiskers can be generated in-situ,
It was also found that impregnation of the sintered body with molten Si can provide whisker composite ceramics of any shape.

[0032]

According to the present invention, it is possible to provide a whisker composite ceramic having improved fracture toughness by dispersing whiskers without impairing the strength and function of the matrix.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a whisker composite ceramic shown as an example of the present invention.

FIG. 2 is a sectional view when the composite ceramic shown in FIG. 1 is used as a mixed powder filling.

FIG. 3 is a characteristic diagram showing a relationship between an initial relative density of a raw material powder packing and an amount of whiskers generated after sintering.

FIG. 4 is a characteristic diagram showing bending strength and fracture toughness of the whisker composite ceramics of FIG. 1 and a comparative material.

[Explanation of symbols]

1 matrix particles, 2 whiskers, 3 pores, 4 ...
Whisker raw powder.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tsuneyuki Kanai 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (56) References JP-A-10-87375 (JP, A) JP-A-64-33077 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/80

Claims (2)

(57) [Claims] 1. A method for producing a whisker composite ceramic obtained by mixing a ceramic powder and a dispersed whisker raw powder and reacting the raw powder in a ceramic firing process to form a whisker in the ceramic. 20% to 60% relative density
A method for producing a whisker composite ceramics, characterized by controlling to the following values. 2. The dispersed whisker raw material powder according to claim 1, wherein the raw material powder is Si ₃ N ₄ , SiO ₂ , C, polycarbosilane, Al ₂
One or more selected from O ₃ , Ar, N ₂ , C
A method for producing a whisker composite ceramic, comprising sintering in at least one atmosphere selected from O, CO ₂ , CH ₄ , H ₂ , and O ₂ or in a vacuum.