JPS62132753A - Method of forming whisker preform - 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 is applicable to the production of fiber-reinforced composite materials by infiltrating or impregnating matrix materials such as metals, alloys, or various plastics. The present invention relates to a method of molding a whisker preform to be used.

[Conventional technology]

W using whiskers such as StC, 5f3N, etc. as a reinforcing material.
An effective compounding method for producing RP or WRM is a method in which a liquid matrix is press-fitted into a preform of pre-shaped whisker aggregates and then solidified. The properties of the composite material obtained by this method largely depend on the tissue structure of the whisker preform, which serves as the fibrous skeleton, and particularly on the degree of homogeneity thereof. Furthermore, in order to mass-produce composite materials using this method, it is an important requirement to quickly and accurately form a whisker preform as an intermediate.

The whisker preform is formed using a wet forming method (Japanese Patent Laid-Open No. 59-12
1196, 59-12049) and a dry molding method (Japanese Patent Application Laid-Open No. 60-46336) in which whiskers are directly compressed and shaped into a predetermined aggregate, but the latter dry molding method is more effective in terms of process. is more suitable for mass production.

[Problem that the invention seeks to solve]

However, when using the dry molding method, stress remains inside the texture during the process of compressing the whiskers, and this residual stress may cause the molded product to springback and deform when the pressure is released, or cause the matrix to deform. There is a problem in that inconvenient phenomena such as damage to the preform occur during the press-fitting process.

These phenomena can be prevented by compressing the whiskers with various binders to forcibly solidify the whiskers together, but the use of binders not only inhibits the homogeneity of the preform structure, but also This poses problems such as weakening the bond with the components or lowering composite performance due to chemical reactions at the interface.

[Means for solving problems]

The present invention solves the above problems and provides a dry molding method for obtaining a whisker preform with a homogeneous structure without residual stress without using a binder.
Thoroughly defibrate the dried whiskers and put them into a mold.
After compression molding to a predetermined fiber volume fraction (Vf), water or an organic solvent is infiltrated into the compressed molded body to moisten the entire body, and the formed wet molded body is dried. Features.

As the whiskers, non-metallic single crystals such as SiC, SisN 4 or graphite can be effectively used.

These whiskers typically have a diameter of 0.1 to 5.0μ1
They are microfibers with an aspect property of 10 to 500 μm in length, and in a fluffy state, they tend to entangle in water or in a humid atmosphere.

For this reason, the whiskers are thoroughly dried and then sufficiently defibrated to loosen the agglomerates before use. For this defibration treatment, a mechanical stirring device such as a swirling blade mixer is used, for example.

The whiskers that have undergone the drying and defibration treatment described above are then compression molded. In compression molding, whiskers are placed in a mold (metal mold or rubber case) of a desired shape and compression molded to a predetermined fiber volume fraction (Vf) using an appropriate press device such as ram pressurization or hydrostatic pressurization. .

Next, water or an organic solvent is permeated into the molded body while maintaining the compressed state to wet the entire tissue. This operation is carried out by directly injecting an appropriate amount of water or organic solvent into the mold, or by vaporizing it and injecting it, but if left for a while, it will easily permeate throughout the mold due to capillary action.

The formed wet molded body is released from the mold and then dried to remove penetrating water or organic solvent.

By the above operation, a whisker preform with a homogeneous structure without residual stress is formed.

[For production]

According to the present invention, residual stress inside the tissue is removed very smoothly by the wetting action of penetrating water or an organic solvent into the compressed compact. In addition, since the above-mentioned wetting process is performed in a compressed state, whisker aggregation does not occur at this stage, and this, combined with the effect of using sufficiently dried and defibrated whiskers, functions to form a homogeneous structure. do.

〔Example〕

m2ZnF+~IFlr1mM, large! '1n～Innr
SiC whiskers having a zttr density of 3, 18 g/ctx" and a β-type crystalline property were thoroughly dried and thoroughly defibrated by stirring with a rotary blade mixer. The defibrated SiC whiskers 1209 were placed in a cylinder with an inner diameter of 80 ii. It was placed in a mold and set in a compression press, and ram pressure was applied from above until the height of the molded body reached 75 mm.Next, while maintaining this compressed state, it was pressed 108 mm from the periphery of the ram. of pure water was injected and left for 30 minutes. During this process, the water penetrated into the molded body and wetted the entire structure.The released wet molded body had a diameter of 8 (ljIm, height 75 m).
It had a normal cylindrical shape of m, and no springback phenomenon was observed.

The formed wet molded body was transferred to a constant temperature dryer maintained at 120° C. and dried for 3 hours to remove moisture.

The SiC whisker preform molded in this manner had a density structure with a fiber volume fraction (Vf) of 10%, and the shape and dimensions were the same as the wet molded product.

For comparison, a SiC whisker preform was molded under the same conditions except that no wet treatment was performed in the above process (comparative example). In this case, when the ram was pulled up after compression molding, the molded product caused springback and swelled to a height of 82 au.

Each of the cylindrical preforms obtained in Examples and Comparative Examples was cut into seven equal pieces, and the fiber volume fraction (Vf) of each sample was measured. Compare the results (table note) Specimen No.
, indicates the cutting position from the top.

From the results in the above table, it was found that the preform structure according to the present invention was extremely homogeneous as a whole compared to the comparative example.

〔Effect of the invention〕

According to the present invention, the disadvantageous phenomenon associated with residual stress within the preform structure, which was a problem with conventional dry molding methods, is eliminated, and a whisker preform with an extremely homogeneous structure as a whole can be molded. be able to. Therefore, it is guaranteed that preforms intended for various high-performance composite materials can always be manufactured with good mass productivity.

Claims (1)

[Claims] Thoroughly defibrate the dried whiskers and put them into a mold.
After compression molding to a predetermined fiber volume fraction (Vf), water or an organic solvent is infiltrated into the compressed molded body to moisten the entire body, and the formed wet molded body is dried. A method for forming whisker preforms.