Surface modification of titanium alloy orthopaedic implants via novel powder immersion reaction assisted coating nitriding method

There is increasing interest in using surface modification technology to im prove the wear properties of titanium alloys used in total joint replacemen ts. In the present work, a simple and original Power Immersed Reaction Assi sted Coating (PIRAC) nitriding method suitable for surface modification of large complex shape orthopaedic implants has been developed. CP Ti and Ti-6 Al-4V alloy samples were annealed at 850-1100 degrees C in sealed stainless steel containers that allow selective diffusion of nitrogen atoms from the atmosphere. The relationship between the microstructure, nitrogen concentr ation and microhardness was studied employing X-ray diffraction (XRD), scan ning electron microscopy (SEM)electron probe X-ray microanalysis (EPMA) and high resolution SEM (HRSEM). PIRAC nitrided surfaces were found to have a layered structure with a TiN/Ti2N coating followed by nitrogen-stabilized a lpha-Ti. In contrast to previous investigations of surface nitrided Ti-6Al- 4V alloy, a Ti,AI intermetallic phase was detected at the Ti2N/alpha-Ti int erface acting as a barrier for nitrogen diffusion. Importantly for biomedic al applications, no toxic Al or V were detected in the surface layer of PIR AC nitrided Ti-6Al-4V alloy. (C) 1999 Elsevier Science S.A. All rights rese rved.