Effect of Powder Morphology and Sintering Atmosphere on the Structure-Property Relationships in PM Processed Co-Cr-Mo Alloys Intended for Surgical Implants

Abstract

This study analysed the possibility of producing biocompatible, porous functionally graded metallic acetabular cups using powder metallurgy techniques, where a porous surface provided a substrate for incorporating a polymeric compliant layer which was supported by a rigid inner core. Two different Co-Cr-Mo powders were investigated, a water atomised powder and a novel bimodal powder; each had a different powder morphology leading to differences in compressibility and sintering behaviour. Suitable combinations of compaction pressure and sintering temperature were used to produce porous materials containing 5–33% total porosity. Moreover, sintering was conducted in three different atmospheres; under vacuum, in flowing argon and in a flowing molecular mixture of 75%H2/ 25% N2. The resulting alloys were subjected to mechanical tests including hardness, tensile strength and ductility. Variations in pore morphology led to differences in surface chromium, bulk nitrogen and carbon content which resulted in marked differences in properties, although the lower the bulk porosity the better the properties exhibited.