(1) Field of the Invention
The present invention relates to preforms as a reinforcement for metal matrix composite (abbreviated as xe2x80x9cMMCxe2x80x9d) materials, a producing process thereof, metal matrix composite materials using said preforms and a producing process thereof.
(2) Related Art Statement
The metallic materials have limitations on improvements in their characteristics, and it is difficult to afford all of two or three contradictory characteristics for a single metallic material. In order to improve the characteristics of metallic materials, fiber-reinforced metal matrix composite materials are proposed, in which fibers are incorporated into the metal. Such a metal matrix composite material has been produced by forming a preform from a so-called reinforcement of such as ceramic particles, ceramic fibers or ceramic whiskers with use of a sol or a fine powder of such as silica or alumina, and then impregnating this preform with a matrix such as aluminum alloys or magnesium alloys.
However, the ceramic particles, ceramic fibers or ceramic whiskers constituting the preform may chemically react with an element or elements in the matrix for the matrix. In this case, the conventional binder dose not has a function to prevent the reaction between the ceramics and the element(s) in the matrix.
As a result, the chemical reaction between the specific element(s) in the matrix and the reinforcement such as ceramic short fibers, particles or whiskers causes the shape of reinforcing material itself, which deteriorates the reinforcement power as the composite material.
Further, the chemical reaction between the specific element(s) such as magnesium, in the matrix and the whiskers changes the concentration of the element(s) in the matrix. This causes the deterioration of the aging hardening ability of the matrix. Therefore, it is important to prevent the chemical reaction between the element(s) and the ceramic short fibers in producing the metal matrix composite material. However, such a preventing method or such a metal matrix composite material having its reinforcement highly maintained has not been known to date.
It is an object of the present invention to provide a preform of ceramic particles, short fibers and/or whiskers, as a reinforcement, which can prevent a reaction between a mother metal as a matrix.
Further, it is another object of the present invention is to provide a metal matrix composite material of which characteristics such as strength are improved by preventing a reaction between a matrix and a preform of ceramic particles, short fibers and/or whiskers.
Furthermore, it is a further object of the present invention is to provide methods for producing the above preform and the metal matrix composite materials, respectively.
In order to solve the above objects, the present inventors came to discover the preform, the metal matrix composite material, and their producing methods through trials to produce thin, condense spinel phase at interfaces between a binder and oxide type short fibers, particles or whiskers by chemically reacting the binder and the reinforcement. The reinforcement is ceramic, and comprises short fibers, particles or whiskers. The short fibers and whiskers usually have lengths of 10xcx9c1000 xcexcm, and diameters of 1xcx9c100 xcexcm. The particles have usually diameters of 1xcx9c100 xcexcm.
The porous preform comprises at least one kind of preform-forming materials selected from ceramic particles, ceramic fibers or ceramic whiskers, and a binder applied on a surface of said at least one kind of the preform-forming materials, said binder comprising magnesium or a magnesium. The binder may be applied in a form of a film on that surface of at least one kind of the preform-forming materials.
As a preferred embodiment of the porous preform according to the present invention, the ceramic particles, the ceramic fibers and the ceramic whiskers comprise an oxide capable of forming a film through a reaction with the binder material(s).
As another preferred embodiment of the porous preform according to the present invention, said magnesium or magnesium alloy reacts with preform-forming materials of ceramic fibers, the ceramic particles and/or the ceramic whiskers, and then forms a film of spinel structure at the interface between the reinforcement and matrix.
As a further preferred embodiment of the porous preform according to the present invention, the ceramic particles, ceramic fibers and ceramic whiskers comprise aluminum borate.
The method for producing a porous preform according to the present invention, comprises the steps of preparing a porous mass of at least one kind of porous preform-forming materials of ceramic particles, ceramic fibers and ceramic whiskers, applying magnesium or a magnesium alloy as a binder on a surface of said at least one kind of the preform-forming materials, and heat-treating the resulting porous preform, thereby forming a thin and uniform spinel phase on said surface. The thus formed spinel phase comprises a spinel structure-possessing compound. The Mg or Mg alloy may be applied by vapor deposition.
As a preferred embodiment of the porous preform-preform producing method according to the present invention, the ceramic particles, ceramic fibers and ceramic whiskers are comprised of oxide materials, which can react with binder material(s) and form the film as a product.
As another preferred embodiment of the porous preform-preform producing method according to the present invention, the ceramic particles, ceramic fibers and ceramic whiskers comprise aluminum borate.
As another preferred embodiment of the porous preform-preform producing method according to the present invention, the vapor deposition of magnesium to the reinforcement is effected under vacuum.
The metal matrix composite material comprising the porous preform, and a metal continuous phase made of at least one kind of metal selected from the group consisting of aluminum, an Alxe2x80x94Si alloy, an Alxe2x80x94Cu based alloy, an Alxe2x80x94Mg based alloy, an Alxe2x80x94Sixe2x80x94Cu based alloy, and an Alxe2x80x94Sixe2x80x94Mg based alloy, an Mg-based alloy and an Mgxe2x80x94Zr based alloy, the metal continuous phase replacing the voids in the porous preform.
A preferred embodiment of the metal matrix composite material according to the present invention, comprises a porous preform, and a metal continuous phase made of at least one kind of metals selected from the group consisting of aluminum, an Alxe2x80x94Si based alloy, an Alxe2x80x94Cu based alloy, an Alxe2x80x94Mg based alloy, an Alxe2x80x94Sixe2x80x94Cu based alloy, an Alxe2x80x94Sixe2x80x94Mg based alloy, an Mg-based alloy and an Mgxe2x80x94Zr based alloy, said metal continuous phase replacing the voids in the porous preform, said preform being prepared by the steps of preparing a porous mass of at least one kind of porous preform-producing materials of ceramic particles, ceramic fibers and ceramic whiskers, and vapor depositing magnesium or a magnesium alloy on surfaces of said at least one kind of the porous preform-forming.
As another embodiment of the metal matrix composite material according to the present invention, the coated magnesium or magnesium alloy reacts with the reinforcement and then forms a film of spinel structure as a product of the reaction.
As a further preferred embodiment of the porous preform-preform producing method according to the present invention, the ceramic particles, ceramic fibers and ceramic whiskers comprise aluminum borate.
The method for producing the metal matrix composite material according to the present invention, comprises impregnating the porous preform with a melt of aluminum or an aluminum alloy.
A preferred embodiment of the method for producing the metal matrix composite material according to the present invention, comprises the steps of preparing a porous mass of at least one kind of a porous preform-forming material of ceramic particles, ceramic fibers and ceramic whiskers, vapor depositing magnesium or a magnesium alloy on surfaces of the at least one kind of the porous-preform material, and heat-treating the resulting porous mass, thereby forming a thin and uniform spinel phase on the surfaces, and impregnating the porous preform with a melt of aluminum or an aluminum alloy.
As a preferred embodiment of the metal matrix composite material according to the present invention, the impregnation is effected under pressure or with no pressurization.
As another preferred embodiment of the metal matrix composite material according to the present invention, the impregnation is effected by a squeeze casting method.
These and other objects, features and advantages of the invention will appreciated upon reading of the following description of the invention when taken in conjunction with the attached drawings, with the understanding that some modifications, changes and variations may be easily made by the skilled person in the art.