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

The 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.