Fatigue Life Enhancement in Alpha/Beta Ti-6Al-4V after Shot Peening: An EBSD and TEM Crystallographic Orientation Mapping Study of Surface Layer

Shot peening is a well-established surface treatment technique to improve metallic components’ fatigue lives by introducing compressive residual stress at their surface layers. Using α/β Ti–6Al–4V alloy as an example, the fatigue life of Ti64 was significantly enhanced after a compressive residual stress was introduced to a depth of 208 µm via shot peening treatment. The top ~24 µm layer from surface was found interestingly unable to be indexed under electron backscatter diffraction (EBSD), a depth coinciding with the presence of maximum compressive residual stress as revealed by center hole drilling method. Transmission electron microscope (TEM) with crystallographic orientation mapping was therefore employed to probe the top surface layer in order to unveil the origin of such thick non-indexed region observed in EBSD after shot peening and its effect on enhancement of component's fatigue life.