Dry friction and wear behavior of forged Co-29Cr-6Mo alloy without Ni and C additions for implant applications

Kazushige Kumagai, Naoyuki Nomura, Tsukasa Ono, Masahiro Hotta, Akihiko Chiba

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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-γ phase to an hcp-ε 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.

Original languageEnglish
Pages (from-to)265-274
Number of pages10
JournalNippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals
Issue number4
Publication statusPublished - 2006 Apr


  • Biomaterials
  • Cobalt-chromium-molybdenum alloy
  • Forged cobalt-chromium-molybdenum alloy
  • Medical implants
  • Wear
  • Wear mechanism
  • Wear resistance


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