Influence of heat treatments on microstructure and mechanical properties of laser additive manufacturing Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy

The effect of heat treatments on laser additive manufacturing (LAM) Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy (TC17) was studied aiming to optimize its microstructure and mechanical properties. The as-deposited sample exhibits features of a mixed prior β grain structure consisting of equiaxed and columnar grains, intragranular ultra-fine α laths and numerous continuous grain boundary α (αGB). After being pre-annealed in α+β region (840 °C) and standard solution and aging treated, the continuous αGB becomes coarser and the precipitate free zone (PFZ) nearby the αGB transforms into a zone filled with ultra-fine secondary α (αS) but no primary α (αP). When pre-annealed in single β region (910 °C), all α phases transform into β phase and the alloying elements distribute uniformly near the grain boundary. Discontinuous αGB and uniform mixture of αP and αS near grain boundary form after subsequent solution and aging treatment. The two heat treatments can improve the tensile mechanical properties of LAM TC17 to satisfy the aviation standard for TC17.