JPH0269365A - Fiber-reinforced composite sintered compact - Google Patents

Abstract

PURPOSE:To increase the effect of addition of SiC whiskers by using SiC whiskers with scarce lamination defect in the crystal structure, having a specified aspect ratio and by composing it with ceramic material. CONSTITUTION:The silicon carbide whiskers having 2-100 aspect ratio and <=0.2h1/h2, where h1 and h2 are peak intensities of 2H type (100) and 3C type (200) of crystalline structure in curve of X-ray diffraction, respectively, are mixed and dispersed in the ceramic powder. After molding, the molded body is sintered to obtain fiber-reinforced composite sintered compact. In this case, the smaller peak intensity ratio h1/h2 results in more scarce lamination defect and the whiskers having >0.2 aspect ratio does not show the sufficient effect of addition of the whiskers. When the whiskers have <2 aspect ratio, they have a smaller effect of crack deflection and drawing in the composite body. On the other hand, when the aspect ratio is more than 100, the whiskers are difficulty dispersed in the matrix and that causes the lowering of strength of the composite body.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvements in fiber-reinforced composite sintered bodies using silicon carbide whiskers.

[Prior art]

Ceramic materials have traditionally attracted attention as materials with excellent mechanical strength such as strength, wear resistance, and oxidation resistance.
Its fatal flaw is its high brittleness, which prevents its full use as a structural material.

Therefore, in order to overcome the brittleness of ceramic materials, attempts have been made to disperse and contain ceramic whiskers with high Young's modulus and high strength in ceramics to improve the toughness against fracture.

In particular, since silicon carbide whiskers have excellent high-temperature strength and high-temperature oxidation resistance, studies are being conducted on dispersing them in ceramic sintered bodies.

Generally, methods for producing silicon carbide whiskers are broadly divided into methods that reduce Sing and methods that utilize reactions in the gas phase. The former method involves mixing the ash residue of grasses with carbon black, heat-treating the mixture at high temperature in a non-oxidizing atmosphere, and producing it by direct reaction (Japanese Patent Application Laid-open No. 57-209813), and the method described in Journal of Materia Is 5.
science 20 p1160-1166 (1985
), there are methods to generate it using the VLS mechanism, and the latter include 5iC1a +CC1*, CH35
A method of producing IC12 and the like by thermally decomposing it in a hydrogen stream is known.

[Problem that the invention seeks to solve]

However, when a composite sintered body is produced using silicon carbide whiskers obtained by conventional methods, the improvement in mechanical strength such as toughness is not noticeable as a result of whisker addition, and the original effect of whisker addition is insufficient. As a result of investigating the cause, we found that one of the causes was the presence of many stacking faults in the whisker itself.

That is, when compounding, the original properties of silicon carbide whiskers are not brought out and no significant improvement in properties has been achieved due to the deviation from the theoretical strength due to the above-mentioned defects.

[Purpose of the invention]

The main purpose of the present invention is to solve the above problems, and specifically, to provide a fiber-reinforced composite sintered body with high strength and high toughness, in which the effects of dispersed addition of silicon carbide whiskers are fully exhibited. It is in.

[Means for solving problems]

As a result of repeated research into the above-mentioned problems, the inventors of the present invention have found that by using silicon carbide whiskers that have a specific aspect ratio and few stacking faults in the crystal structure, and by combining this with a known ceramic material. It has been found that a composite sintered body can be obtained in which the original effects of whisker addition, such as high strength and high toughness, have been sufficiently achieved.

That is, the present invention provides silicon carbide whiskers that have an aspect ratio of 2 to 100 and a crystal structure that increases the (100) peak intensity of the 2H type in an X-ray diffraction curve.
When the peak intensity of type (200) is h2, h1
It is characterized by using a material having a peak intensity ratio expressed by /h2 of 0.2 or less and dispersing it in a ceramic material to form a composite.

Hereinafter, the present invention will be explained in detail with reference to FIG.

Figure 1 shows the Cu- α
FIG. 3 is a diagram showing an X-ray folding pattern using lines. As is clear from Fig. 1, the X-ray diffraction pattern of conventional silicon carbide whiskers includes a (100) peak of hexagonal 2H type SiC near 2θ = 34 (deg), and
There is a composite peak of 211 (002) and 3C (101) near 2θ = 36 (deg), and a peak of 2θ = 41.5 (deg).
30 types of 5iC (200
) peaks are clearly observed.

The silicon carbide whiskers used in the present invention are characterized by the 2H type (1
When the peak intensity of 00) is hl and the peak intensity of 30 type (200) is h2, the intensity ratio expressed by h1/h2 is 0.2 or less, and the aspect ratio is 2 to 2.
It is at a point where it is 100.

The smaller the value of this peak intensity ratio, the fewer the stacking faults.If the peak intensity ratio exceeds 0.2, the strength of the whisker decreases due to the large number of stacking faults, and the When creating a composite, the effect of whisker addition cannot be fully brought out. In addition, if the aspect ratio is smaller than 2, the deflection of the crank as a whisker in the composite and the pulling effect of the whisker will be reduced, and if the aspect ratio exceeds 100, it will be difficult to disperse into the matrix, and conversely, the strength will deteriorate. invite

On the other hand, various well-known materials can be used as ceramics capable of dispersing the silicon carbide whiskers, and specifically, silicon carbide compositions using compounds such as boron, carbon, aluminum, and group IIa elements as auxiliaries are applicable. A silicon nitride composition, an Alz (h-base composition, a ZrO2-base composition, a cermet-based composition, a w-base cemented carbide composition, etc.) can be used in combination as desired.

The amount of silicon carbide whiskers added to the ceramic as a matrix varies somewhat depending on the matrix used, but it should be adjusted to a level that does not significantly deteriorate the properties of the matrix, and it is desirable to add it at a rate of about 5 to 30% by volume. .

In manufacturing the composite sintered body, a well-known method may be adopted depending on the matrix component to be used. For example, the matrix component and the whisker component may be individually dispersed in an organic solvent such as alcohol by adding a dispersant etc. if desired. After that, both are mixed at a predetermined ratio to prepare a mixed slurry, and this slurry is dried, molded, and fired.

In addition, in manufacturing the silicon carbide whiskers mentioned above, compared to conventional silicon carbide whiskers that contain many stacking faults,
Heat treatment is performed in a non-oxidizing atmosphere at 1800 to 2300°C. By this heat treatment, large defects in the Mi layer of whiskers can be reduced. If the heat treatment temperature is lower than 1800°C, the effect of reducing stacking faults will be small, and if it exceeds 2300°C, sublimation of silicon carbide will occur, which is not preferable.

Furthermore, although this heat treatment has the effect of reducing stacking faults, it also causes a phenomenon in which the aspect ratio of whiskers decreases. This phenomenon becomes more pronounced as the processing temperature increases. Therefore, by allowing carbon to coexist during heat treatment, it is possible to suppress the decrease in aspect ratio and to control stacking faults.

Carbon is supplied by adding carbon powder such as carbon black or an organic compound that generates carbon by thermal decomposition such as phenol resin, or by using a carbon atmosphere by using a carbon crucible or the like during heat treatment. However, in order to control the aspect ratio and stacking faults, it is desirable to add carbon powder or organic compounds.

The atmosphere in the heat treatment needs to be non-oxidizing, but it is particularly desirable to carry out the heat treatment under reduced pressure or in an inert gas such as argon gas, and the heat treatment may also be carried out in a gas pressurized atmosphere. However, nitrogen gas is undesirable because the surface of the whisker is nitrided and silicon nitride is produced.

The invention will now be explained with the following examples.

〔Example〕

Commercially available silicon carbide whiskers were used and subjected to heat treatment under different processing conditions to create six types of whiskers with different aspect ratios and peak intensity ratios as shown in Table 1. The ht/ht intensity ratio is calculated from the peak intensity ratio h1/h2 of 2H (100) and 3C (200) from X-ray diffraction measurement using alpha rays on Cu-, and the aspect ratio is S8M.
Obtained by observation.

(blank below) Table 1 Furthermore, the composition shown in Table 2 was used as a matrix.

Table 2 Kerr was subjected to dispersion treatment using an ultrasonic disperser using alcohol as a solvent and a dispersant to obtain a dispersion slurry.

These two slurries were mixed and dried in the proportions shown in Table 3,
After molding, pot pressing was performed under the conditions shown in Table 3 to obtain a sintered body. After polishing each sintered body, JISR1601 4
The bending strength was measured by a point bending bending test, and the toughness was measured by a microindentation method.

The results are shown in Table 3.

(Hereinafter referred to as #color) (Numbers are molar ratios) The ceramic powders shown in Table 2 above were mixed in a ball mill using alcohol as a solvent to obtain a uniformly dispersed mixed slurry. On the other hand, as is clear from the results in Table 1 and Wiss Table 3, the aspect ratio of silicon carbide whiskers exceeds 100, and sample 1 using F
As is clear from the comparison with Samples 1 to 3, Samples 4 to 16 and Samples 21 to 23 have bending strength and fracture toughness that are approximately the same or have deteriorated. Also, the peak intensity ratio is 0.2
Samples 17 to 20 in which E exceeds 20% show the effect of improving toughness, but the level thereof is slight.

On the other hand, samples 4 to 13 of the present invention all exhibited excellent bending strength and fracture toughness, with a bending strength of 960 MPa or more and a fracture toughness of 8.3 MPa for matrix (A).
``The bending strength is 950t against the matrix (b).
A composite sintered body having a fracture toughness of 8.2 MPam"" or more, a flexural strength of 800 MPa or more and a fracture toughness of 7.2 MPam"" or more relative to the matrix (c) was obtained.

〔Effect of the invention〕

As detailed above, the composite sintered body of the present invention uses specific silicon carbide whiskers with an aspect ratio of 2 to 100 and few stacking faults as whiskers, and by dispersing and containing them in a matrix made of ceramics, While maintaining the original strength of the whiskers, sufficient crack deflection and whisker pulling effects can be achieved with respect to the matrix components, thereby obtaining a fiber-reinforced composite sintered body with excellent flexural strength and fracture toughness. First thing you can do
figure

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the X-ray diffraction patterns of conventional silicon carbide whiskers (A, B) and the silicon carbide whisker (C) of the present invention.

Claims (1)

[Claims] Ceramic powder has an aspect ratio of 2 to 100 and a crystal structure of 2H type (10
When the peak intensity of 0) is h_1 and the peak intensity of 3C type (200) is h_2, a molded body made of silicon carbide whiskers with a peak intensity ratio expressed by h_1/h_2 of 0.2 or less is fired. A fiber-reinforced composite sintered body.