The Unlubricated Sliding Wear Behavior of a Wrought Cobalt-Chromium Alloy Against Monolithic Ceramic Counterfaces

Abstract

The unlubricated sliding wear and friction behavior of a wrought cobalt-chromium alloy against sintered Al2O3, ZrO2-toughened Al2O3, MgO-partially-stabilized ZrO2, and hot-pressed Si3N4 ceramic counterfaces has been investigated. Both untreated (baseline) and surface-borided conditions of alloy 6B disks were investigated. The dominant wear and/or material degradation mechanism for surface-borided alloy 6B was a combination of abrasion and plastic deformation; in addition, adhesive transfer of the cobalt alloy to monolithic Al2O3 counterfaces was a significant wear mechanism for the as-solution-treated alloy 6B disk. For the partially stabilized ZrO2 counterface, the degradation mechanism involved thermal and/or mechanical fatigue processes, resulting in the formation of microcracks in the 6B disks transverse to the sliding direction. This microcracking has been ascribed to the low thermal conductivity of the partially stabilized ZrO2 and the activation of a martensitic, fcc-to-hcp transition with each passing of the ZrO2 ball. For borided alloy 6B against hot-pressed Si3N4, a transition from negligible to severe wear was noted with increasing sliding speeds.