JP2519076B2 - Method for manufacturing silicon carbide whisker-reinforced ceramics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention requires high hardness, high strength and high toughness such as cutting tool materials and automobile engine members such as ceramic valves and heat engine members such as gas turbine rotors. The present invention relates to a method for producing silicon carbide whisker reinforced ceramics suitable for various structural members.

(Prior Art) A material in which silicon carbide (SiC) whiskers are compounded with a ceramic material having excellent properties such as Al ₂ O ₃ and Si ₃ N ₄ to improve strength and toughness and reliability is studied. Was there. See, for example, JP-A-60-200863, JP-A-60-24628, and JP-A-61-270266.

However, it cannot be said that the materials having such a level have sufficiently obtained various characteristics.

(Problems to be Solved by the Invention) According to the research conducted by the present inventors, even if SiC whiskers are compounded with a conventional ceramic having A1 ₂ O ₃ or Si ₃ N ₄ as a matrix phase,
There is a limit to the increase in toughness because the interfacial reaction between the glass phase generated by the mother phase or the sintering aid and the SiC whiskers causes a bond that cannot exert the pullout effect of the SiC whiskers. Was recognized.

In the above, the pull-out effect means that in the stress field at the crack tip generated in the matrix ceramics, the pull-out phenomenon of whiskers occurs, and the stress concentration at the crack tip is significantly reduced, resulting in high toughness. This phenomenon depends largely on the bonding state between the matrix phase and the dispersed phase (here, the matrix phase or the glass phase and the whisker interface).

An object of the present invention is to achieve this pullout effect and to achieve toughness of ceramics.

[Means for solving the problem]

The present invention has been made as a result of various studies in view of the above-mentioned circumstances, and improved SiC whiskers, and by using an SiO ₂ content of 0.01% by weight or more and 2.0% by weight or less by acid treatment, it can be avoided conventionally. On the other hand, it was found that a strong bond due to a chemical reaction at the interface between the matrix phase and the glass phase and the whiskers is suppressed, an appropriate bond state is obtained, and thereby the pullout effect is sufficiently exerted and high toughness is achieved. Has produced the following manufacturing method.

That is, the SiO ₂ content is 0.01% by weight or more due to the acid treatment.
After molding a compounded composition obtained by uniformly dispersing and mixing 5 to 40% by weight of SiC whiskers of 2.0% by weight or less and the ceramic powder mainly composed of Al ₂ O ₃ by the usual method, 1650
A method for producing a silicon carbide whisker reinforced ceramics which is sintered in a non-oxidizing atmosphere at -1900 ° C., whereby a toughened silicon carbide whisker reinforced ceramics is obtained. In addition, in the above ceramic powder, carbides of IVA, VA, and VIA group elements of the periodic table as additives,
It may contain 0 to 30% by weight of one or more nitrides or borides.

Here, in general, carbides, nitrides, or borides of IV A, VA, and VI A group elements have high hardness and excellent wear resistance, do not react with Al ₂ O ₃ matrix, and suppress grain growth. Is also known to have the effect of.

Therefore, there is generally no problem even if it is added up to a certain amount.
However, the sinterability decreases as the amount added increases.
Up to 30% by weight is desirable.

(Function) SiO ₂ content in SiC whiskers is 0.01 wt% or more
Control to 2.0% by weight or less can be achieved by acid treatment with HF or HF + HCl.

Further, in the present invention, the reason why the SiO ₂ content of the SiC whiskers is 0.01% by weight or more and 2.0% by weight or less is as follows.
_{2 If the} content is less than 0.01% by weight, the wettability between the SiC whisker and the mother phase becomes too poor, and the sinterability is reduced, which is not preferable, and if it exceeds 2.0% by weight, a mother phase or a mother phase is formed. The reaction between the glass phase and SiO ₂ generated by the sintering additive added for the purpose becomes remarkable, and the bonding force at the interface between the glass phase and the whiskers increases, so cracks project inside the whiskers before the whiskers pull out, It is not preferable because it progresses so as to escape and the strengthening by the addition of whiskers cannot be achieved.

The starting material used in the present invention is SiC whiskers having an average diameter of 0.2 to 5 μm, an average length of 5 to 30 μm, and an aspect ratio of 2 to 150. The whiskers include Al, Ca, Mg, Ni, Fe. It is preferable to use a whisker-shaped crystal containing 1.0% by weight or less of cation impurities such as Mn, Co, and Cr and having less scratches, branching, and plane defects in order to obtain a highly tough and dense sintered body.

 Next, the compounding ratio specified in the present invention will be described.

The reason why the amount of SiC whiskers added is 5 to 40% by weight is that if the SiC whiskers are less than 5% by weight, there is almost no effect of adding whiskers to the ceramic sintered body.
No improvement in strength and toughness is observed, and on the other hand, when it exceeds 40% by weight, the anisotropy of the whiskers decreases the uniform dispersibility and the sinterability also decreases significantly. It is 10 to 30% by weight.

Example 1 A silicon carbide whisker having a SiO ₂ content of 3.0% by weight was immersed in a mixed solution of HF (1 + 1) + HCl (1 + 1) at room temperature,
By changing the treatment time, silicon carbide whiskers having different SiO ₂ contents were obtained as shown in Table 1. The SiO ₂ content of the treated silicon carbide whiskers was measured according to JIS R6124.

Next, each silicon carbide whisker obtained, average particle size 1.0 μm, α-Al ₂ O ₃ powder with a purity of 99.99%, average particle size 2.0
Powders of TiC, TiN, TiB ₂ , TaC, and ZrB _{2 having} a particle size of less than or equal to μm were mixed at the ratio shown in the first ratio, uniformly dispersed and mixed in ethanol for 16 hours, dried, and granulated. A base powder was obtained.

This base powder was pot pressed in a graphite mold under the conditions shown in Table 1 to obtain a dense sintered body. The obtained sintered body is 4m
After polishing to a size of m × 3 mm × 40 mm, the fracture toughness was measured by JIS R1601 with a bending strength and a load of 30 kg by an indentation microfracture method. The results obtained are shown in Table 1.

From these results, it was found that a high toughness sintered body having excellent oxidation resistance can be obtained by adding 5 to 40% by weight of silicon carbide whiskers having an SiO ₂ content of 0.01% to 2.0% by acid treatment. It was

(Effects of the Invention) As can be seen from the above, according to the manufacturing method of the present invention, it is possible to easily manufacture a ceramic having high toughness and improved oxidation resistance.

Claims (1)

(57) [Claims] 1. A SiO ₂ content of 0.01% by weight or more due to acid treatment.
After forming a compounded composition in which 5 to 40% by weight of silicon carbide whiskers less than 2.0% by weight and a ceramic powder mainly composed of A1 ₂ O _{3 as the} balance are formed uniformly, 1650 ° C to 1900 ° C
The method for producing silicon carbide whisker reinforced ceramics, which comprises sintering in a non-oxidizing atmosphere.