Production of porous sintered Co-Cr-Mo alloys for possible surgical implant applications .2. Corrosion behaviour

In the first part of this study, data were presented for the compaction, sintering, and mechanical properties of a water atomised cobalt based alloy and a bimodal mixture of ball milled ASTM F75 plasma rotating electrode process powder blended with the cobalt based alloy powder. In the present study, the corrosion of these two powders was compared for a range of compacts of varying porosity between 6 and 35% total porosity and between 0.5 and 26% interconnected porosity under conditions which simulated in vitro body fluid conditions. Differences in microstructure and surface composition caused by reactions with three different sintering atmospheres, e.g. loss of chromium, decarburisation, or Cr2N formation, altered the corrosion behaviour. The worst corrosion resistance occurred in compacts sintered in molecular 75H(2)-25N(2) (by volume) gas, while argon atmosphere sintered compacts were the most resistant to corrosion. Pore size and pore geometry also had a considerable influence on the corrosion behaviour and the corrosion resistance tended to improve with decreasing porosity.