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

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.