Post-plasma-spraying heat treatment of the HA coating/Ti-6A1-4V implant system.

The metal/ceramic interface that constitutes an important part of the plasma-sprayed HA-coated Ti-6A1-4V system may, in fact, represent the "weak link" in the implant design. A post-plasma-spray heat treatment to enhance chemical bonding at the metal/ceramic interface and, hence, improve the mechanical properties (interface fracture toughness and tensile coating adhesion strength) of the plasma-sprayed implant system does show promise. In preliminary heat treatment studies, however, any improvements realized were lost due to the chemical instability of the coating in a moisture-laden environment, with a concomitant loss in bonding properties. This deterioration in properties appears to be related to environmentally assisted crack growth as influenced by processing conditions. Still, an ability to improve HA/Ti-6A1-4V bonding through enhanced diffusion bonding was demonstrated, warranting further heat treatment studies involving atmosphere control during processing.