JPH04333536A - Production of whisker preform - Google Patents

Abstract

PURPOSE:To render high strength in spite of low density texture by heating an aggregate of silicon carbide whiskers formed into a prescribed shape in an oxidizing atmosphere. CONSTITUTION:Silicon carbide whiskers as a base material are formed into an aggregate of a prescribed shape by utilizing entwinement and this aggregate is heated at 600-1,500 deg.C, preferably 800-1.200 deg.C in an oxidizing atmosphere. During this heating, thin oxidized films of silicon dioxide are formed on the surfaces of the whiskers, melt-bonded numerous points of contact of the whiskers and convert the texture of the aggregate into integrated tough texture without affecting the density. Though the aggregate has low density texture of 3-25vol.% density, the strength against bending, comrpession, etc., is enhanced.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention produces whisker-reinforced metal composites (W) by infiltrating matrix materials such as metals and alloys.
The present invention relates to the production of whisker preforms used as reinforcing materials when obtaining RM), and particularly relates to a method for producing whisker preforms that have high skeletal strength against shrinkage and cracking even if they have a low density structure.

0002

[Prior art] W using acicular crystal whiskers as a reinforcing material
As a composite means for manufacturing RM, a method is known in which a preform of a preformed collection of whiskers is infiltrated with a molten matrix and solidified. The properties of the composite material obtained by this method greatly depend on the properties of the whisker preform that forms the fibrous skeleton, and in particular, the density and homogeneity of the structure greatly control the composite performance, so research and development regarding the formation of the preform is It has been widely practiced ever since.

[0003] The most effective method for forming whisker preforms is to disperse the whisker product in water or an organic solvent, filter this under normal pressure or pressure, and then use the remaining wet whisker cake as it is or Filtration molding method of compressing and then drying (Japanese Patent Application Laid-Open No. 59-121
No. 196, JP-A-60-161400). Using this method, it is relatively easy to adjust the density by selecting filtration conditions and the degree of compression, and the resulting preform has the advantage of exhibiting a homogeneous structure even though it is an aggregate of whiskers. However, there is a drawback that sufficient tissue strength cannot be ensured. Particularly in low-density tissues where the volume content (Vf) of whiskers is 15% or less,
During compositing, shrinkage and deformation occurs when the matrix material is press-fitted, making it impossible to obtain the desired volume content, or cracks and fractures occur, resulting in failure to form a normal composite structure.

[0004] In order to solve the above problems, many methods have been proposed in which the preform is loaded with various binder components to strengthen its structure. The binder component includes
Inorganic systems include colloidal silica, water glass, boric acid,
Alkali metal borates or aluminates, etc., and organic agents such as silane coupling agents, carboxymethyl cellulose, sodium alginate, or a mixed aqueous solution of these and acrylic acid are used.

[0005]

[Problems to be Solved by the Invention] However, the presence of a binder component as described above causes various disadvantages such as reaction with the matrix substance, inhibition of smooth tissue penetration of the matrix, and deterioration of interfacial wettability with the matrix. It causes the phenomenon. Moreover, it also becomes a negative factor in terms of manufacturing process and cost.

[0006] An object of the present invention is to provide a method for producing a whisker preform having high strength performance even with a low density structure without using a binder component.

[0007]

[Means for Solving the Problems] A method for manufacturing a whisker preform according to the present invention to achieve the above object is to produce an aggregate of silicon carbide whiskers that have been formed into a predetermined shape using entanglement in an oxidizing atmosphere. Inside 600-150
A structural feature is that the heat treatment is performed at a temperature of 0°C.

The whisker serving as the base material of the present invention is composed of an acicular single crystal of silicon carbide, and its manufacturing history and properties do not matter. Therefore, the diameter exceeds 2 μm,
Even if the whisker has an aspect ratio of less than 30 and is difficult to entangle, it can be used as a base material.

[0009] In order to form silicon carbide whiskers as a base material into an aggregate of a predetermined shape, for example, the whiskers are dispersed in water or an organic solvent and then filtered and formed using a pressure-type filtration device of a predetermined shape. A filtration molding method in which a wet whisker cake is dried as it is or compressed to a predetermined density.
Appropriate methods include the slurry casting method, in which a dispersed slurry of whiskers is molded in a water-absorbent mold of a predetermined shape, and then dried, and the semi-dry pressure molding method, in which the whiskers are press-molded in a mold with some moisture and dried. Shaping means can be applied. However, in order to form a low-density texture, it is preferable to use a filtration molding method. Furthermore, for the purpose of the present invention, the density of whisker aggregates is determined by the volume content (Vf
), an excellent reinforcing effect is imparted when the low density structure is 3 to 25%, particularly 15% or less.

[0010] The aggregate of silicon carbide whiskers formed by the above-described forming means by utilizing the intertwining of the whiskers is then heat-treated in an oxidizing atmosphere. This heat treatment is a process to oxidize the surface of the silicon carbide whiskers that make up the aggregate, and is usually carried out by placing the whisker aggregate in an electric furnace kept in the air and raising the temperature. can. The heating temperature at this time is 600-1500℃, preferably 800-1200℃
Set within range to ℃. If the heating temperature range is less than 600°C, the strengthening function of the structure will be insufficient, and if it exceeds 1500°C, surface oxidation will progress too much, which will conversely lead to a decrease in tissue strength.

[0011]

[Operation] According to the present invention, silicon dioxide is formed on the surface layer of the whiskers in the process of heat-treating an aggregate of silicon carbide whiskers, which has been formed into a predetermined shape using the intertwining of the whiskers, in an oxidizing atmosphere. A thin oxide film forms. The silicon dioxide coating layer that is produced fuses the numerous contact points where the whiskers come into contact with each other, transforming the whiskers into a solid, integrated structure without affecting the tissue density.

Through the above-mentioned action, the strength performance against bending, compression, etc. is dramatically improved even in a whisker aggregate with a low-density structure, so that shrinkage deformation and cracking occur even when molten matrix metal is press-fitted during composite formation. It becomes possible to manufacture a whisker preform that does not cause such phenomena as the above.

[0013]

[Examples] Examples of the present invention will be explained below in comparison with comparative examples.

Examples 1-2, Comparative Example 1 Diameter 0.2-0.5 μm, aspect ratio 50-1
00 β crystal type silicon carbide whisker 72g to 1 part water
000 ml and thoroughly stirred for homogeneous dispersion. Using a cylindrical airtight filtration device, compressed air was poured in from the top for 30 minutes.
．． Pressure filtration was carried out while feeding at a pressure of 5 kg/cm2. The resulting wet whisker cake was then air-dried and further dried at a temperature of 150° C. to form a disc-shaped whisker aggregate with a diameter of 80 mm. The volume content of this aggregate (
Vf) was 9%, and the bending strength was 1.8 kgf/cm2.

The above silicon carbide whisker aggregate was cut into test pieces with a diameter of 80 mm and a thickness of 10 mm, which were placed on a magnetic plate and placed in a Kanthal furnace, and heated at 400° C., 600° C. and 1100° C. in an air atmosphere. Heat treatment was performed at each temperature of 1 hour. Table 1 shows the results of a bending test performed on each test piece after cooling.

[0016]

[Table 1]

From the results in Table 1, it can be seen that in Comparative Example 1, the heat treatment temperature was below 600°C, so the bonding effect due to the formation of an oxide film was insufficient, and the bending strength was hardly improved compared to the untreated whisker aggregate. unacceptable. On the other hand, a clear increase in strength was observed in the Examples, and in particular, in Example 2 treated at 1100° C., the bending strength increased dramatically.

Example 3, Comparative Example 2 The silicon carbide whisker preform obtained in Example 2 was set in a mold, and an Al alloy (AC8A) heated and melted at 800° C. was poured into the mold at a heating rate of 1000 kg/cm2. It was made into a composite using a molten metal forging method using pressure. The volume content (Vf) of whiskers and the volumetric shrinkage rate of the preform in the composite part measured after cooling and solidification were as shown in Table 2. For comparison, Table 2 also lists the results (Comparative Example 2) obtained when a whisker aggregate that was not subjected to heat treatment (untreated product) was composited under the same conditions as above.

[0019]

[Table 2]

From Table 2, it is found that the whisker preform according to Example 3 has an extremely small increase in volume content (Vf) during compounding and a very small volume shrinkage due to compressive deformation compared to Comparative Example 2.

[0021]

[Effects of the Invention] As described above, according to the present invention, a low-density structure with a volume content (Vf) of 15% or less can be obtained by subjecting a preformed silicon carbide whisker aggregate to a simple heat treatment. It is also possible to form a high-strength whisker preform that does not undergo compressive deformation or cracking during composite formation. Therefore, it is particularly useful as a manufacturing technology for whisker preforms for composite materials aimed at silicon carbide whisker-reinforced metal materials with a low volume content.

Claims (2)

[Claims] [Claim 1] An aggregate of silicon carbide whiskers, which has been formed into a predetermined shape using entanglement, is heated in an oxidizing atmosphere.
A method for producing a whisker preform, the method comprising heating at a temperature of 600 to 1500°C. 2. The method for producing a whisker preform according to claim 1, wherein a silicon carbide whisker aggregate having a volume content (Vf) of 3 to 25% is used.