High‐cycle and very‐high‐cycle fatigue behavior at two stress ratios of Ti‐6Al‐4V manufactured via laser powder bed fusion with different surface states

Abstract

AbstractThe high‐cycle fatigue (HCF) and very‐high‐cycle fatigue (VHCF) behavior of Ti‐6Al‐4V manufactured by laser powder bed fusion (L‐PBF) was investigated to reveal the effects of surface roughness and stress ratio on fatigue performance. Fatigue tests were performed by an ultrasonic vibration machine with a frequency of 20 kHz. The fatigue strength of surface‐polished specimens is generally higher than that of as‐built specimens in HCF and VHCF regimes. Fatigue cracks initiated from the subsurface of as‐built and surface‐polished L‐PBF Ti‐6Al‐4V. The values of size and depth for the defects that acted as fatigue crack origins present large scattering for L‐PBF Ti‐6Al‐4V due to the interaction between surface roughness and subsurface defects. For surface‐polished L‐PBF Ti‐6Al‐4V, fatigue cracks have almost the same resistance to propagation at both stress ratios of R = −1 and 0.7.