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

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 surfacepolished L-PBF Ti-6Al-4V, fatigue cracks have almost the same resistance to propagation at both stress ratios of R = À1 and 0.7. K E Y W O R D Slaser powder bed fusion, stress ratio, surface roughness, Ti-6Al-4V, very-high-cycle fatigue Highlights• Fatigue strength of surface-polished specimens higher than as-built L-PBF Ti-6Al-4V • Fatigue crack initiation from lack-of-fusion defects in subsurface defectenriched layer • Defect & surface roughness with greater effect on crack initiation than stress ratio • Crack propagation much easier in as-built than surface-polished L-PBF Ti-6Al-4V

Guest editorial of virtual special issue: The eighth international conference on very high cycle fatigue (VHCF8), held online from July 5 to 9, 2021, and distributed from Sapporo, Japan

“…Fu et al 13 investigated the fatigue behavior of Ti‐6Al‐4V produced by laser powder bed fusion (L‐PBF) under high‐cycle and very‐high‐cycle conditions. They used an ultrasonic fatigue testing machine with a 20 kHz frequency to determine the impact of surface roughness and stress ratio on fatigue performance.…”