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A dry wear behavior of a forged Co-Cr-Mo alloy without Ni and C additions have been investigated using a ball-on-disc type wear testing machine with an alumina ball in ambient air. The wear factor of the Co-Cr-Mo forged alloy without Ni and C additions (hereafter, designated the forged alloy) shows negative contact load dependence. The coefficient of friction decreases with increasing contact load. Worn surfaces are hardened during the wear tests, forming oxide films. This results from significantly high work hardening rate of the forged alloy, caused by the strain-induced martensitic transformation from an fcc-phase to an hcp-" phase, which contributes to the improvement in the dry wear resistance.Wear mechanisms of the forged alloy are discussed on the basis of Hertzian contact theory and observations of the wear scars formed on the alloy disc and the alumina ball surfaces. It is considered that the dominant wear mechanism of the forged alloy is the mild adhesive wear, though the extrinsic abrasive wear mediated by the wear debris, i.e., third-body abrasive wear, is exerted as an extrinsic wear mechanism. In addition, it is suggested that a delamination wear resulting from the fatigue fracture likely occurs under the present dry wear condition.

The wear behavior of a forged Co-29Cr-6Mo alloy without any Ni and C added has been investigated by using a tribosystem consisting of a pin-on-disc type wear testing machine in distilled water containing different dissolved oxygen content. Dissolved oxygen content in the distilled water was controlled by aerating with oxygen or by deaerating with argon. Wear volume in the distilled water containing high oxygen content is approximately two times larger than in that containing low oxygen content. Accordingly, it is deduced that the overall wear volume is significantly affected by the dissolved oxygen content in the distilled water surrounding the tribosystem. Although abrasive wear, caused by wear debris, is operative as a wear mechanism in the present tribosystem irrespective of oxygen content, the transfer of the wear debris to sliding surfaces, as well as the aggregation of the wear debris on the sliding surfaces, is more prone to occur during the wear process with the lower oxygen content. Therefore, in the present tribosystem with the lower oxygen content, since the transfer of the wear debris to the disc or the pin readily occurs, the generation of the wear debris does not directly contribute to the wear volume, leading to the apparently lower wear volume in the tribosystem with lower oxygen content than in that with higher oxygen content; the transfer of the wear debris is not counted as wear loss because the wear volume is estimated based on the loss in disc and pin weight that occurs during the wear test.