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 Ra 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.

Keywords: titanium, laser powder bed fusion, Fatigue, Orientation-dependency, X-ray Computed Tomography