JP2686795B2 - Titanium carbide-based composite sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention is used for a heating element material, a cutting tool material, and a wear resistant member, and particularly to a titanium carbide based composite sintered body having improved oxidation resistance. .

[Conventional technology]

Titanium carbide is known as a material having excellent properties such as high strength, high hardness, high toughness, and electrical conductivity. On the other hand, the oxidation resistance is extremely poor.

JP-A-59-78973 and JP-A-5-78973 are known to improve the oxidation resistance while taking advantage of the advantages of titanium carbide.
No. 9-91685 discloses that titanium carbide and alumina are compounded. Alumina is a material having high strength, high hardness, and excellent oxidation resistance, but low fracture toughness. This is to combine the drawbacks of both titanium carbide and alumina by compounding them and to take advantage of their advantages.

However, the above-mentioned composite material cannot be said to have sufficiently improved oxidation resistance. That is, when the composite material is oxidized, aluminum titanate is formed, but since the anisotropy of thermal expansion is remarkable, this becomes an oxide film accompanied by microcracks. The oxide film does not serve as an oxidation protection film due to cracks, and oxidation progresses significantly inside the composite material.

Also in the case of a composite material of titanium oxycarbide and alumina, the oxidation resistance is not sufficient as in the above case.

[Problems to be solved by the invention]

When a conventional titanium carbide-alumina composite sintered body is used as a heating element used in an oxidizing atmosphere or as a cutting tool material for cutting at high speed, oxidation resistance is required but not sufficient.

Therefore, a method of coating the surface of the sintered body with alumina by the CVD method has been adopted. However, the coating film of the CVD method may crack or peel off due to the cycle,
There is a problem that oxidation progresses rapidly from that part.

The present invention has been made to solve the drawbacks of the conventional method, and an object of the present invention is to provide a novel titanium carbide-based composite sintered body having greatly improved oxidation resistance as compared with the conventional method.

[Means for solving the problem]

That is, the titanium carbide-based composite sintered body of the present invention has a composition containing 10 to 60 wt% of titanium carbide and / or titanium oxycarbide and 3 to 10 wt% of magnesium oxide, and the balance of alumina and inevitable impurities. It is characterized in that 15 to 75 mol% of magnesium oxide has an oxidation protection film formed as a solid solution in aluminum titanate.

Here, when the titanium carbide and / or titanium oxycarbide is less than 10% by weight, the fracture toughness, electric conductivity, and hardness of the obtained sintered body become small, and when it exceeds 60% by weight, a high density is not obtained. It is not preferable because it has poor oxidation resistance.

If the amount of magnesium oxide is less than 3% by weight, the amount of magnesium oxide that forms a solid solution in the formed aluminum titanate will be small, and dense oxidation protection without microcracks cannot be obtained. If the amount of magnesium oxide is more than 10% by weight, the density will not be high and the oxidation resistance will be poor, such being undesirable. The oxidation protective film formed from this composition was a dense oxide protective film with no microcracks, in which 15 to 75 mol% of magnesium oxide was solid-dissolved in aluminum titanate.

[Operation / configuration]

The conventional composite sintered body of titanium carbide and alumina is
As described above, aluminum titanate is produced on the surface when oxidized. This aluminum titanate had a remarkable thermal expansion anisotropy, and a sufficient oxidation protection film was not formed due to the occurrence of cracks.

In the present invention, by combining titanium carbide and / or titanium oxycarbide with alumina and magnesium oxide to form an oxidation protection film of aluminum titanate in which magnesium oxide is solid-solved, conventional titanium carbide-alumina composite materials are obtained. Oxidation resistance is greatly improved compared to the sintered body.

It is known that when magnesium oxide is solid-dissolved in aluminum titanate, the thermal expansion anisotropy disappears and microcracks disappear. That is, the titanium carbide based composite ceramics according to the present invention has a dense oxidation protection film of aluminum titanate having a solid solution of magnesium oxide having no thermal expansion anisotropy and no microcracks. Even if oxygen enters, titanium oxide and / or titanium oxycarbide in the assembly, alumina and magnesium oxide react with each other to form a similar aluminum oxide titanate protective film. Therefore, the invasion of oxygen is suppressed and the oxidation resistance is improved.

 Hereinafter, the present invention will be described with reference to examples.

[Example 1] Titanium carbide having an average particle diameter of 1.5 µm and a particle diameter of 0.2 µ
m alumina powder and 0.01 μm magnesium oxide powder having different weight ratios were mixed in six kinds. This mixed powder was molded into pellets, embedded in alumina powder at 1850 ° C. in an argon stream and sintered under normal pressure.

Table 1 shows the relative density of the obtained sintered body and the composition of the oxidation protection film after heat treatment at 1400 ° C. for 2 hours in the atmosphere.

Next, the above sintered body was allowed to stand at 1500 ° C. in air, and the weight change was measured.

The results are shown in Fig. 1. That is, the examples according to the present invention are sample Nos. 3, 4, and 5, and No. 1 and 2 having little weight change but a small amount of magnesium oxide have a large oxidative weight increase and a large amount. 6 has a low density and a large oxidation weight gain. The present invention significantly improves the oxidation resistance by adding an appropriate amount of magnesium oxide (3 to 10% by weight).

Example 2 Using a titanium carbide powder having an average particle diameter of 1.5 μm, an alumina having an average particle diameter of 0.2 μm and a magnesium oxide powder having an average particle diameter of 0.01 μm, a sintered body was obtained by mixing three kinds shown in Table 2 below. It was As a sintering method, in an argon stream
A method of embedding in alumina powder at 1850 ° C. and sintering under normal pressure was used.

Table 2 shows the results of measuring the relative density, room temperature conductivity, 3-point bending strength, and fracture toughness of the above samples.

As shown in the above table, the sintered body of this example has excellent electrical conductivity,
It was a high-strength ceramic. Fracture toughness was maximum at 30% TiC, but decreased at 60% TiC, probably because the relative density was 93.5%, which was not densified.

〔The invention's effect〕

As described above, the present invention significantly improves the oxidation resistance of the titanium carbide-based composite sintered body as compared with the conventional one. The sintered body according to the present invention is a material having high electrical conductivity, high hardness, high strength, and high fracture toughness, and since it is provided with oxidation resistance, it can be used as a heating element that can be used in an oxidizing atmosphere or can be cut at high speed. It is particularly useful as a tool material to be used.

[Brief description of the drawings]

FIG. 1 is a graph showing the weight increase when the example of the present invention was left at 1500 ° C. in the atmosphere. 3, 4, 5 ... Examples according to the present invention 1, 2, 6 ... Comparative examples

Claims (1)

(57) [Claims] 1. Titanium carbide and / or titanium oxycarbide 10 to 60% by weight, magnesium oxide 3 to 10
A titanium carbide-based composite calcination, characterized in that it has a composition comprising alumina and unavoidable impurities, and that 15 to 75 mol% of magnesium oxide has an oxide protective coating in solid solution in aluminum titanate. Union.