Carbide surface coating of Co-Cr-Mo implant alloys by a microwave plasma-assisted reaction

A technique to grow a hard carbide surface coating on Co-Cr-Mo implant alloys used in artificial joints was developed. The carbide surface coating was applied to as-cast and forged Co-Cr-Mo alloys to improve their wear properties. The surface carbide layers were produced by reactions between the alloy surface and a methane-hydrogen mixed gas by a microwave plasma-assisted surface reaction. The new carbide layers showed “brain coral-like” surface morphology and appear to consist of mixed phases including Cr3C2, Cr2C, Cr7 C3, Cr23C6, and Co2C. The Vickers microhardness of thin carbide coatings (∼3 μm thick) was about HV 1100 regardless of the test location. The Vickers microhardness of thick carbide coatings (∼10 μm thick) showed a wide range of hardnesses from HV 1000 to HV 2100. Co-deposition of soot and diamond films occured on a small area of the forged alloy substrates and diamond particles were sparsely dispersed on as-cast alloy substrates. The carbide surface layer has the potential to increase the wear resistance of the Co-Cr-Mo alloy as a wear resistant coating.