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 beta grain structure consisting of equiaxed and columnar grains, intragranular ultra-fine alpha laths and numerous continuous grain boundary alpha (alpha(GB)). After being pre-annealed in alpha+beta region (840 degrees C) and standard solution and aging treated, the continuous alpha(GB) becomes coarser and the precipitate free zone (PFZ) nearby the alpha(GB) transforms into beta zone filled with ultra-fine secondary alpha (alpha(S)) but no primary alpha (alpha(P)). When pre-annealed in single beta region (910 degrees C), all alpha phases transform into beta phase and the alloying elements distribute uniformly near the grain boundary. Discontinuous alpha(GB) and uniform mixture of alpha(P) and alpha(S) 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.