Evaluation of microstructure and mechanical properties of additively manufactured Ti–5V–5Mo-5 Al-3 Cr alloy

Ti–5V–5Mo–5Al–3Cr (Ti-5553) is a near-beta titanium alloy commonly used in aerospace applications. It is currently being explored for additive manufacturing (AM), but the fatigue behavior of this AM alloy needs to be well-understood for adoption. This paper explores the tensile and high-cycle fatigue behavior of laser powder bed (LPBF) manufactured Ti-5553 that has been post-print heat treated with a beta anneal and age (BAA), with a focus on the microstructural evolution and effects of surface roughness and print defects. Fatigue lives of as-LPBF and BAA material are nearly identical and both are far below fatigue lives of conventionally manufactured Ti-5553. As-built samples contain columnar β grains with a [001] texture in the build direction with a negligible fraction of α phase confirmed by electron backscatter diffraction (EBSD). The BAA material contains HCP alpha-phase precipitates: grain boundary α, primary α, and secondary Widmanstätten α. Fatigue samples were printed in the vertical direction and tested with an as-printed and machined surface. Both the as-LPBF and BAA samples exhibit similar fatigue strengths despite their vastly different microstructures. Machined surfaces led to an increase in tensile strength, ductility, and fatigue strength. This work emphasizes the importance of heat treatment and minimization of flaws inherent to AM processing of near-beta Ti-5553.