Abstract
The coefficient of friction and the wear resistance of three types of alumina, that is, single crystals of sapphire (α-Al2O3), polycrystalline sintered alumina and sintered abrasive grits, on a dry stainless steel surface have been determined as a function of sliding speed. As the results, it is found that the wear of single and polycrystalline alumina appears to occur by both mechanisms, that are consisted of attritious wear with plastic flow over 20 m/s of sliding speed and fragmentation below 10 m/s, whereas the sintered abrasive grits are worn mostly by attrition with less wear rate even at low sliding speed, although, at high sliding speed, the wear is greatly increased with decreasing the bonding force of grains owing to high temperature during sliding. It is associated that the attritious wear in the single and polycrystalline alumina may be produced by chemical reactions occuring in the wear layer under high sliding speed. Also, the fragmentation resistance of alumina depends on crystallographic orientation such as plane of wear and rubbing directions, and existence of grain boundary, so that the wear resistance of the single crystals of sapphire under low sliding speed is less than that of the polycrystalline alumina.
