On the Effect of the Stress Ratio on Fatigue Properties of Ti-6Al-4V Produced by Laser Powder Bed Fusion

Fatigue life estimation of Ti-6Al-4V parts produced by additive manufacturing (AM) technologies has received increasing interest during the last decade. Recent studies focused mostly on the fatigue performance of Ti-6Al-4V considering a fixed stress ratio ( $R$ ), usually 0.1 or −1. However, in order to properly design structural components subjected to variable loads, the effect of different stress ratios on the fatigue performance has to be carefully investigated. This research studies the stress ratio influence on the fatigue properties of Ti-6Al-4V specimens produced by laser powder bed fusion (L-PBF). Miniaturized Ti-6Al-4V samples were tested with the step procedure for different $R$ values. A constant life Haigh's diagram ( $2·10^6$ cycles) was generated for L-PBF Ti-6Al-4V in as-built, electro-polished, and machined surface condition. The results present for the first time the relations between alternating and mean stresses for L-PBF Ti-6Al-4V with a fine $\alpha +\beta$ microstructure when different surface posttreatments are used to enhance the coupons’ final surface quality.