Fretting of CoCrMo and Ti6Al4V Alloys in Modular Prostheses

Cobalt and Titanium based alloys are two most commonly used alloys in Total Hip Arthroplasty. The Cobalt alloy (Co28Cr6M) is commonly used as the head component of the Hip device whilst the Titanium alloy (Ti6Al4V) is used as the stem component. This paper assessed the failure mechanisms of both alloys under fretting conditions. The fretting contact was modelled using a ball-on-plate configuration at a contact pressure of 1 GPa serum containing solution. It was observed that the CoCr-CoCr fretting contact encouraged a gross slip fretting regime from as low as 25µm of displacement amplitude whereas, for the CoCr-Ti fretting contact at 25µm, a stick regime was observed. This indicated that CoCr-CoCr fretting contact degrades through a wear dominated mechanism whilst CoCr-Ti degrades through a fatigue dominated mechanism. The slip at the contact was shown to effect the removing of the protect oxide layer of both passive alloys.

钴基合金与钛基合金是全髋关节置换术（Total Hip Arthroplasty）中最常用的两类合金。钴合金（Co28Cr6M）通常用作髋关节装置的头部组件，而钛合金（Ti6Al4V）则用作柄部组件。本文评估了两种合金在微动条件（fretting conditions）下的失效机制。微动接触采用球-盘构型（ball-on-plate configuration）建模，接触压力为1 GPa，环境为含血清溶液。观察发现，CoCr-CoCr微动接触在位移振幅低至25µm时即进入整体滑移微动状态（gross slip fretting regime）；而CoCr-Ti微动接触在25µm位移振幅下则处于黏着状态（stick regime）。这表明CoCr-CoCr微动接触通过磨损主导机制退化，CoCr-Ti则通过疲劳主导机制退化。接触处的滑移被证明会去除两种钝化合金的保护性氧化层。