PRODUCTION OF POROUS SINTERED CO-CR-MO ALLOYS FOR POSSIBLE SURGICAL IMPLANT APPLICATIONS .1. COMPACTION, SINTERING BEHAVIOR, AND PROPERTIES

The compaction and sintering behaviour of a coarse water atomised cobalt based alloy and a bimodal mixture of ball milled ASTM F75 plasma rotating electrode process powder with the cobalt alloy powder is reported. The techniques employed were intended to generate a porous substrate, using cold compaction techniques, on which a polymeric surface layer could be mechanically bonded. Suitable combinations of compaction pressure and sintering temperature were shown to generate porosities in the bimodal mixture equivalent to those obtained with coarse water atomised powder, producing considerable improvements in green strength over the latter. Sintering in different atmospheres caused variations in surface chromium, nitrogen, and carbon content. Atmospheres that prevented decarburisation, e.g. argon, encouraged liquid phase sintering to occur at high temperatures (>1340 degrees C) via a carbide eutectic reaction; while nitriding and decarburisation effects also caused differences in hardness. The measured effects of porosity on Young's modulus showed good agreement with a theoretical model. (C) 1995 The Institute of Materials.