Microstructural dependence of tribological properties of Ti-6Al-4V ELI alloy after slide burnishing / shot peening and low-temperature gas nitriding

Abstract

Ti-6Al-4V ELI alloy was subjected to different types of sequential, mechanical and thermochemical pre-treatments. Turning, slide burnishing and two variants of shot peening were performed on the heat treated samples prior to low temperature gas nitriding. Subsequently, all the samples modified in this way were subjected to a microstructure characterization as well as assessment of hardness and sliding wear properties. Scanning electron microscopy analysis revealed the samples which have undergone slide burnishing and shot peening exhibited a modified near surface microstructure with the formation of burnishing affected zone (BAZ) and shot peening affected zone (SPAZ) which extended the wear resistance of the alloy. Further, TEM observations indicated the formation of a thin amorphous TiN ‘tribo-layer’ above these zones. Finally, as a consequence of the shape and size of particles within BAZ and SPAZ combined with the tribo layer led to the enhancement of tribological and mechanical properties of titanium alloys.