COEFFICIENT OF FRICTION UNDER DRY AND LUBRICATED CONDITIONS OF A FRACTURE AND WEAR-RESISTANT P M TITANIUM-GRAPHITE COMPOSITE FOR BIOMEDICALAPPLICATIONS/

Recent studies have shown that aseptic loosening of orthopaedic implan ts is a biomechanical phenomenon initiated mechanically and propelled by biological responses to the presence of wear debris released from t he biomaterial. A triphasic composite, fabricated by the heterogeneous sintering of titanium and graphite powders was developed to address t he fracture and wear performance of titanium. The composite is designe d to smear graphite on both articulating surfaces and hence reduced we ar and maintained a low friction tribosystem with fracture properties better than conventional bioceramics. The composite is made up of duct ile titanium and a colony of hard, wear resistant titanium carbide pro duced by the controlled sintering of titanium and graphite particles. Free graphite is present in varying quantities depending upon compacti on pressure and initial graphite composition. Initial graphite content composites of 4% and 8% were made with different compaction pressure to give a range of porosities from 10% to 45%. The coefficient of fric tional was measured on a pin-on-disc (hardened steel) configuration. U nder dry state, the coefficient of friction was observed to reduce wit h increasing porosity. Graphite smearing and the entrapment of debris by the pores contributed to the reduction of the wear components which in rum reduced the coefficient of friction. Under lubricated conditio ns, the sintered titanium and its composites were observed to be indep endent of porosity and pore size. The frictional behaviour of the tita nium-8% graphite composites showed first, a titanium carbide dominated -wear stage and the second, a free graphite smearing stage. The result s proved the concept that the coefficient of friction of titanium-grap hite composites approaches that between graphite-graphite surfaces aft er the running-in period. This proof of concept is the first realisati on of a biomaterial that could reduce the coefficient of friction on b oth articulating surfaces, a step closer to the development of fractur e and wear resistant biomaterials that also protects the other counter surface. (C) 1998 Elsevier Science S.A.