Additively manufactured Ti-5Al-5V-5Mo-3Cr: Understanding defect-fatigue relationships

Ti-5Al-5Mo-5V-3Cr (Ti-5553), a near-beta Ti alloy, possesses an excellent combination of strength, toughness, and strength-to-weight ratio, and due to its poor machinability characteristic, it is poised to be additively manufactured for key structural applications. This study examines the micro-/defect-structure and mechanical behavior, including both tensile and fatigue, of laser powder bed fused Ti-5553. The tensile and fatigue specimens are fabricated in two locations on the build plate with respect to the powder feed direction, i.e., west (away from powder reservoir) and east (near powder reservoir), to examine the location dependence of the mechanical properties. In addition, fatigue specimens are furnished in both un-machined and machined surface conditions. It is found that the volumetric defect content is higher for the west specimens than the ones in the east; however, tensile and fatigue properties are not affected by part location. The insensitivity of fatigue lives to the part location can be ascribed to specimens having statistically equivalent defect size distribution near the surface, as fatigue failures are primarily initiated by critical defects on or in the vicinity of the surface in un-machined and machined specimens.