Additively manufactured Ti-6Al-4V microstructure tailoring for improved fatigue life performance

Abstract

In this study, laser powder bed fusion (LPBF)-produced Ti-6Al-4V is subjected to three separate post-build heat treatments (HTs), specifically (1) a one-step annealing HT exceeding the (Formula presented.) -transus temperature, (2) a two-step annealing HT whose first step exceeds the (Formula presented.) -transus temperature and the second step is an anneal below the (Formula presented.) -transus temperature, and (3) a sawtooth HT with temperatures oscillating below the (Formula presented.) -transus temperature. Tensile properties and fatigue crack growth behavior were assessed and compared to wrought Ti-6Al-4V. LPBF materials nominally exhibited a 17% yield stress reduction, 1.9% strain-to-failure increase, and 9.2% modulus of toughness decrease. Fatigue crack growth curves were used to assess the linear crack growth rate region and approximate fracture toughness ((Formula presented.)). Post-mortem fractography observed striations indicating the crack growth direction frequently changes direction providing an understanding of the slower crack growth rates observed in LPBF materials compared to their wrought counterpart.