Orientation matters: Assessing the cyclic deformation behaviour of laser powder bed fusion Ti-6Al-4V

Abstract

The orientation dependency of the fatigue behaviour of laser powder bed fusion Ti-6Al-4V has been analyzed and rationalized. Seven build orientations relative to the build plate have been studied. The 75° specimen demonstrates the highest fatigue life owing to the optimal surface quality and low proportions of grains near-parallel to the loading direction. When the build orientation is 30° or below, only defects on the downward-facing surface serve as the fatigue crack initiation sites as a result of the poor surface quality. Beyond 45°, cracks begin to initiate from the otherward-facing surface owing to the reduced variation in $R_a$ across the sample surface. The large variation in the size and number of pore clusters near the initiation site governs the highest fatigue scatter of the 75° specimen whereas the difference in crack initiation sites of the 45° specimen results in the large difference in fatigue life. Our results demonstrate that the orientation effect is a critical factor to consider for the design of fatigue-tolerant intricate components.