Effect of Heat Treatment on the Fatigue of Laser-Powder Bed Fused Ti-6Al-2Sn-4Zr-2Mo Alloy

Abstract

This study investigates the effect of heat treatment on the monotonic and fatigue behavior of laser-powder bed fused Ti-6Al-2Sn-4Zr-2Mo. The as-built microstructure consists of acicular α’ martensite, featured with dense dislocations that result in high strength and low ductility. To preserve the microstructure and achieve strength–ductility synergy, a two-step sub-transus heat treatment is selected: solutionizing (ST) below the β-transus temperature and aging (STA). The ST heat treatment results in the evolution of α/α’ and β phases, with good strength–ductility synergy. The STA treatment causes the dislocations to rearrange, accompanied by a slight strength enhancement. The STA condition showed a small improvement in fatigue life in the high-cycle regime but demonstrated minimal changes compared to the as-built condition for low- to mid-cycle regions. The low and mid-cycle fatigue life of as-built and STA conditions showed noticeably similar results to wrought Ti-6Al-4V fatigue behavior.