Tensile and fatigue behaviors of additively manufactured Ti-6Al-4V: Influence of surface texture and removal

Abstract

This study examined the influence of four different surface material removal treatments on the tensile and fatigue behaviors of laser powder bed fused Ti-6Al-4V specimens. These treatments included direct polished, shallow machined and polished, deep machined, and deep machined and polished. X-ray computed tomography was used to characterize the surface textures and volumetric defects of each condition, and scanning electron microscopy was used for fractography of all failed specimens. The results showed that tensile ductility and fatigue resistance were strongly influenced by the type of material removal methods. Direct polishing did not improve the tensile ductility nor fatigue lives due to remnant surface valleys. While the combined shallow machined and polished specimens exhibited significant improvement in ductility due to adequate removal of surface anomalies, fatigue lives were only modestly enhanced due to the persistence of surface-connected volumetric defects. However, deep machined and combined deep machined and polished treatments led to considerable improvement in both ductility and fatigue resistance, which was ascribed to complete removal of surface and subsurface defects. In addition, fatigue life was modeled and estimated using a fatigue notch factor approach, which yielded reasonably accurate predictions for the untreated, polished, and shallow machined and polished specimens.