Compositions: ceramic – Ceramic compositions – Refractory
Patent
1999-09-09
2000-10-17
Group, Karl
Compositions: ceramic
Ceramic compositions
Refractory
501 87, 501 93, 501 961, C04B 35117, C04B 3556
Patent
active
061331821
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to alumina base ceramics excellent in wear resistance with high hardness, high strength and high toughness, and particularly suitable for a cutting tool or a wear resistant member.
BACKGROUND OF TECHNOLOGY
Such alumina base ceramics have been used as a cutting tool or a wear resistant member for high-speed machining and hot working where a conventional tool material such as a tool steel, a high-speed steel, a cemented carbide or the like is difficult to use, because of its comparable easiness for producing a compact sintered body among conventional ceramic materials.
However, the alumina base ceramics is disadvantaously limited in use because of their poor strength and toughness.
Sintered Al.sub.2 O.sub.3 dispersion-strengthened with carbide or carbo-nitride particles such as TiC or Ti (C,N) in order to improve the properties, so-called black ceramics have been developed. However, such black ceramics is lack in reliability when applied for machining under a heavy load such as rough cutting of steel or cast iron, because of its insufficient strength and toughness.
Further, since a sintered Al.sub.2 O.sub.3 added with WC particles is improved significantly in strength and toughness, and has a high hardness, it has been tried to apply to wear resistant members.
For example, Japanese Patent Laid-Open No. 3-290355 discloses that a high hardness and high toughness sintered body having a density of more than 90% of the theoretical can be provided by subjecting a starting powder consisting of Al.sub.2 O.sub.3 added with 10-90% by volume of WC to normal sinterinig, hot pressing, or hot isostatic pressing.
It is also disclosed in Japanese Patent Laid-Open No. 5-279121 that a sintered body obtained by adding 5-95 wt % of WC to Al.sub.2 O.sub.3 followed by sintering at 1400-1950.degree. C., and making W.sub.2 C phase appear due to existence of oxygen of 0.05-6 wt. % in the WC starting powder is excellent in strength and toughness.
However, these Al.sub.2 O.sub.3 -WC ceramics can not exhibit sufficient wear resistance under a severe condition of high-speed cutting of steel or cast iron, since the oxidation resistance at high temperature is insufficient although it is surely excellent in strength and toughness. Therefore, these ceramics are hardly used for a member requiring high-temperature wear resistance such as cutting tool.
DISCLOSURE OF INVENTION
The purpose of this invention is to provide alumina base ceramics remarkably improved in strength and toughness while preserving excellent oxidation resistance and wear resistance during machining under a severe condition.
This invention provides a dense sintered body of Al.sub.2 O.sub.3 which contains 5-70% by volume of WC and 5-70% by volume of Ti (C,N) solid solution, and this sintered body exhibits high strength, high toughness, and excellent wear resistance even at a high temperature.
Alumina powder having an .alpha.-crystalline phase of 90 vol. % or more and an average particle size of 5 .mu.m or less is preferably used.
The strength and toughness are remarkably improved by adding WC particles to the Al.sub.2 O.sub.3 sintered body. This improvement is resulted from the dispersion strengthening by highly hard WC particles and the toughening by the action of the residual stress due to the difference in thermal expansion coefficient between Al.sub.2 O.sub.3 particles and WC particles caused when the temperature lowers from the sintering temperature to room temperature between the two kinds of grains. The addition of WC to Al.sub.2 O.sub.3 has an effect of suppressing the grain growth in the sintering, whereby the fine grains are maintained to strengthen the sintered body.
The content of WC is determined within the range of 5-70% by volume. When the content of WC is less than 5% by volume, the improvement in strength and toughness of the sintered body is little because of small amount of WC phase. But, when it exceeds 70% by volume, the oxidation resistance at high temperature tends to deteriorate in addition to the difficul
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Inoue Shigeo
Mitomi Shinzou
Nagano Mitsuyoshi
Okuma Eiji
Sasaki Toyoshige
Group Karl
Nippon Tungsten Co. Ltd.
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