JPH03290367A - Production of carbon/silicon carbide composite material - Google Patents

Abstract

PURPOSE:To obtain a composite ceramic structural material having high and stable strength and good lubricity by reacting a green compact composed of graphite powder with a eutectic alloy composed mainly of silicon. CONSTITUTION:A eutectic alloy 2 containing silicon accounting for the major part of the alloy is impregnated under pressure into a green compact 1 composed of graphite powder and made to react with each other to form a silicon carbide layer 3 at the interface between the green compact 1 and the alloy 2 and precipitate an intermetallic compound 2 composed mainly of silicon. The eutectic alloy 2 is e.g. Si-Mo alloy, Si-Nb alloy and Si-Ta alloy and the content of Si is preferably >=80wt.%. The eutectic composition is used in order to lower the melting point and form the intermetallic compound.

Description

[Detailed Description of the Invention] [Summary] The purpose of the present invention is to produce a molded body having high mechanical strength and lubricity with respect to a method for producing a graphite-silicon carbide-based composite material. A eutectic alloy in which silicon accounts for most of the composition ratio is infiltrated under pressure and reacted to form a silicon carbide layer at the interface with the powder compact, and an intermetallic compound mainly composed of silicon is precipitated. A method for producing a graphite-silicon carbide composite material is characterized in that:

[Industrial application field]

The present invention relates to a method for producing a graphite-silicon carbide composite material.

Metals and ceramics are used as materials for bearings that support rotating shafts in mechanical devices. Metals are also called anti-friction alloys or anti-friction alloys, and have a low coefficient of friction.
Materials used are low in wear and have excellent corrosion resistance against lubricating oil and the like.

Bronze-based or iron-based sintered bodies are used and impregnated with lubricating oil.

There are also oil-free bearings that contain graphite or the like to provide self-lubricating properties.

The present invention relates to a ceramic structure that is used in applications that require high mechanical strength and lubricity.

[Conventional technology]

In addition to the above-mentioned alloys, composite ceramics are used in applications such as bearings that require high mechanical strength and lubricity.

For example, alumina (Aj!203) and silicon carbide (SiC)
) Materials are known in which metal particles such as titanium (Ti) or aluminum (^Il) are dispersed as reinforcing substances inside a matrix made of ceramics such as ceramics.

Composite ceramics are produced by molding and sintering ceramic material powder in which reinforcing metal particles are dispersed.

However, since it is a sintered body, there are many pores, which causes large fluctuations in strength, and it is necessary to ensure a high safety factor for practical use.

Furthermore, since the sintering temperature of ceramics is as high as 1500° C. or higher, oxidation of reinforcing metal particles is likely to occur, which is also a cause of large fluctuations in strength.

[Problem to be solved by the invention]

As described above, ceramic composite materials have been known for some time, but they are not used much because of large fluctuations in strength.

Therefore, it is an issue to provide a new composite ceramic structure material that has high strength, little fluctuation, and has lubricity.

[Means to solve the problem]

The above problem was solved by pressure infiltrating a eutectic alloy, in which silicon (hereinafter referred to as Si) accounts for the majority of the composition, into a powder compact made of graphite (hereinafter abbreviated as C) powder and reacting it with the powder compact. This problem can be solved by configuring a method for producing a C-5i composite material characterized by forming a silicon carbide (hereinafter referred to as 5iC) layer on the joint surface and precipitating an intermetallic compound whose main component is silicon. .

[Effect]

The present invention forms a strong SiC film on the surface of a porous powder compact made of C by reacting compacted C with a molten Si alloy. By using a method of filling with intermetallic compounds, composite ceramics with high mechanical strength and lubricity can be realized.

Figure 1 is a diagram of this principle, and shows that C1 that has been compacted has gaps between each particle, and these gaps are filled with eutectic alloy in which the composition ratio of Si is mostly (80% by weight or more) at high temperatures. By infiltrating the melt of No. 2, C1 reacts with the Si constituting the eutectic alloy 2 to form a silicon carbide (SiC) layer 3, and the unreacted Si precipitates an intermetallic compound. It is.

From this table, Si-M is a eutectic alloy that can be used in the present invention.
o (molybdenum) alloy, 5i-Nb (niobium) alloy.

Examples include 5i-Ta (tantalum) alloy.

For reference, FIG. 2 shows a phase diagram of the 5t-1'lo alloy, and FIG. 3 shows a phase diagram of the 5i-Nb alloy.

The reason for using the eutectic composition is that the melting point decreases and
This is to form an intermetallic compound, which is characterized by improving workability and reducing oxidation of Si.

Next, the reason why the Si content of the eutectic alloy used is 80% by weight or more is that as a result of experiments, if the content is less than this, the reaction with C is insufficient and the amount of SiC formed is insufficient. This is because the strength decreases.

The present invention has a 5ieJo++ composition (melting point 1
410″C) and 51″C) in Figure 3.
A eutectic alloy of aeNb+z (melting point 1300°C) is used.

When such a eutectic alloy is infiltrated into a powder compact made of C to change the surface layer to SiC, the composition of the eutectic alloy becomes s
As the in-force ratio shifts to the smaller side, an intermetallic compound of X5iz (X is Mo or Nb) flourishes, and this intermetallic compound contributes to improving the strength.

Note that it is necessary to use a pressurized atmosphere to infiltrate into the molded body.

The present invention coats the surface of C with low hardness with SiC with high hardness, and fills the gaps between particles with an intermetallic compound 2 with high hardness.
When this material is used to construct, for example, a bearing, the C inside will partially appear due to wear, resulting in a composite ceramic with high strength and good lubricity.

〔Example〕

As C, a scale-like material with an average particle size of 10 μm was used.
This powder was 5
The bottom of the press was formed into a plate shape of 50 m x 50 m.

This density was 78%.

Next, Si and M so that the weight U becomes SiavMo+s.

After mixing, the mixture was placed in an alumina crucible and heated to 1320°C, which is 20°C higher than the eutectic temperature of 1300°C, in a nitrogen (N) stream using a high-frequency melting furnace to form a uniform alloy. .

This molten alloy was cast into a mold, and the CtF mold was cut into the same dimensions as the mold body.

This alloy was placed on top of the C molded body, and N2 was placed at a pressure of 100 atm.
By heating at 1300° C. for 10 minutes in an atmosphere, it was infiltrated into the interior and reacted with C to form SiC.

As a result of cross-sectional observation of the obtained sample, the porosity was 0%, all the pores of the molded body were impregnated with molten alloy, and SiC was uniformly formed on the surface of C. The molten alloy remaining in the pores was precipitated as Mo5iz.

Next, when the bending strength of this sample was measured, it showed a value of about 80 Kg/m'', and the variation in the value was slight.

Further, as a result of a wear test, the amount of wear was reduced to about 1/8 compared to SiC alone.

〔Effect of the invention〕

According to the present invention, it is possible to make a composite Cera G7 that has high strength, little variation in strength, and rich lubricity.
It can be applied to structural parts.

[Brief explanation of drawings]

Fig. 1 is a principle diagram of the composite ceramic-nox material according to the present invention, Fig. 2 is a phase diagram of the St-Mo alloy, and Fig. 3 is a phase diagram of the 5i-Nb alloy. In the figure, 1 is C (graphite), 2 is a eutectic alloy (intermetallic compound), and 3 is a SiC layer. Beni-shi1 Weight ('/,) S M. Phase diagram of Mo alloy (X) Si S;

Claims (1)

[Claims] A compact made of graphite powder is infiltrated with a eutectic alloy in which silicon accounts for most of the composition ratio under pressure to cause a reaction, forming a silicon carbide layer at the interface with the compact, and at the same time forming a silicon carbide layer mainly containing silicon. A method for producing a graphite-silicon carbide composite material, which comprises precipitating an intermetallic compound as a component.