Effect of Surface Roughness on Fatigue Strength of Ti-6Al-4V Alloy Manufactured by Additive Manufacturing

This study focuses on the effects of surface roughness on the fatigue strength of Ti-6A1-4V alloy manufactured by additive manufacturing (AM); electron beam melting (EBM) and direct metal laser sintering (DMLS) methods. The hot isostatic pressing (HIP) was applied to some series of polished specimens and as -built specimens to eliminate internal defects. Fatigue limit was evaluated by rotating bending fatigue tests. Although HIP increased the fatigue limits slightly, the fatigue limits of as -built specimens with HIP were only about 30% of the ideal fatigue limit expected from the Vickers hardness. On the other hand, the polished specimens with HIP had the fatigue limit close to the ideal upper bound. The fatigue crack was initiated at multiple sites on the surface in as-built specimens. Thus, surface roughness has crucial influence on fatigue strength of AM component. The surface morphology of as-build specimen is three-dimensionally complex. The evaluation of equivalent defect size for surface roughness was attempt by Varea parameter model assuming the surface roughness is a small defect. The estimated defect size was over the applicable range of the Varea parameter model, suggesting that the surface roughness of as -built specimen should be considered as long crack. 2019 The Authors. Published by Elsevier B.V.