It is well known in the arts that aluminum oxide ceramics may be prepared in relatively low cost and have excellent properties, particularly, in terms of mechanical strength and heat resistance. Accordingly, aluminum oxide has been widely used for in various applications.
As one of the practical applications of the aluminum oxide for mechanical purposes, a part in a machine required having highly wear resistance, for example, materials for tools, sliding parts, etc has been sintered. However, since the requirements on these application becomes severe, the material capable of attaining higher performance are further demanded. In particular, the materials having high wear resistance are desired.
To be comply with such requirements, an attempt is made to improve in wear resistance by adding various carbides into the aluminum oxide.
The material made of aluminum oxide in which various carbides are simply added, generally shows large crystal grains, and does not satisfy the severe requirement since the dislodgement of the grains from the sintered material are liably caused when it is subjected to abrasion. These materials cannot be accepted as having sufficient wear resistance.
The aluminum oxide containing carbides has drawbacks that if the carbide is in an amount of less than 5 wt % shows insufficient wear resistance, and on the other hand, the more the amount of carbides is, the lesser the mechanical strength depending on the carbides becomes.
The reason for the above phenomenon is not clear so far, however, it is considered to be depending on the fact that interfacial bonding between the aluminum oxide grains and various carbides grains is so weak and the aluminum oxide grains are not sufficiently pulverized.
For instances, JP-A-62-59567 (a term "JP-A" used herein means unexamined Japanese patent publication) discloses a ceramic material having excellent were resistance which principally comprises 5 to 20 weight % of titanium carbide and the rest of alumina. Since the titanium carbide, per se. is added as one of the starting materials, the effect according to the present invention in terms of the wear resistance cannot be attained.
JP-A-52-104515 and JP-A-63-129061 are disclosed to prepare alumina/titanium carbide ceramic material, in which titanium carbide is formed by chemical reaction in a firing step, however, no third component, which is required as an indispensable component to fulfill the objects according to the present invention, is present in the composition. Accordingly, the product obtained by the chemical reaction step is these references cannot form pulverized grain of the present invention.
According to the present invention in which these drawbacks are overcome, there is to provide an aluminum oxide based sintered body having excellent properties in terms of mechanical strength and wear resistance, as well as a method for producing the same.