Effect of carbide size on the abrasion of cobalt-base powder metallurgy alloys

A study of the effect of carbide size on the abrasion resistance of two cobalt-base powder metallurgy alloys, alloys 6 and 19, was conducted using low stress abrasion with a relatively hard abrasive, A12O3. Specimens of each alloy were produced with different carbide sizes but with a constant carbide volume fraction. The wear test results show a monotonie decrease in wear rate with increasing carbide size. Scanning electron microscopy of the worn surfaces and of wear debris particles shows that the primary material removal mechanism is micromachining. Small carbides provide little resistance to micromachining because of the fact that many of them are contained entirely in the volume of micromachining chips. The large carbides must be directly cut by the abrasive particles. Other less frequently observed material removal mechanisms included direct carbide pull-out and the formation of large pits in fine carbide specimens. These processes are considered secondary in the present work, but they may have greater importance in wear by relatively soft abrasives which do not cut chips from the carbide phase of these alloys. Some indication of this is provided by limited studies using a relatively soft abrasive, rounded quartz.