DLC coating over pre-oxidized and textured Ti6Al4V for superior adhesion and tribo-performance of hip implant

Abstract

Superior surface characteristics, tribological performance and adhesion strength are critical for DLC coated surface in hip implant. Incorporating laser surface texturing and heat treatment before DLC deposition can improve surface properties by inducing oxygen diffusion and phase formation. Therefore, oriented crosshatch textures were fabricated over Ti6Al4V surface using Nd:YAG laser. Textured surface was heat treated followed by DLC coating deposition with Cr interlayer. Effect of heat treatment over DLC coating morphology, adhesion strength and surface characteristics was analyzed. Phase formation and bonding behavior at the coating interlayer were characterized and correlated with adhesion strength. Bio-tribological performance of modified surface was evaluated under elliptical sliding contact to replicate hip implant articulation. Increased surface roughness, better wettability and enhanced graphitic characteristics were associated with DLC coating with prior heat treatment. With heat treatment, Cr2O3 and TiO2 phase formation with superior bonding at interlayer demonstrated improved adhesion strength including deformation resistance. Textured, heat treated and DLC coated surface showed relatively increased compressive residual stress with HF1 quality adhesion. The synergic effect of surface texturing and DLC coating achieved lowest friction. Qualitative wear analysis using Raman spectroscopy reveals beneficial effect of heat treatment before DLC coating for long term hip implant application.