High-strength titanium alloy with hierarchical-microstructure design via in-situ refinement-splitting strategy in additive manufacturing

Microstructure design of high-strength materials based on single-principal-microstructure advantage can hardly meet the increasingly strict service requirements of modern aviation and aerospace industries. Compared with conventional forming methods, additive manufacturing (AM) technology introduces more regulatory variables, making it possible to gain multiple microstructure advantages simultaneously for critical components. This study introduces a universal process strategy in laser-powder bed fusion (L-PBF) to achieve hierarchical-microstructure optimization for titanium alloys. Specifically, a higher energy density can refine (R) martensite lath, and an appropriate scanning strategy can split (S) both coarse prior-β grains and α'-colony. For L-PBF-fabricated Ti-6Al-4 V (Ti64) alloy, the proposed refinement-splitting (R & S) optimization strategy improved yield strength (up to ∼1.3 gigapascals) by 30% and the total elongation increase by about 1.9 times compared to the alloy samples with a conventional rich α'-colony microstructure. The split prior-β grains also help with the complex service environment by reducing the anisotropy-induced deterioration of mechanical properties. The R&S approach is, in principle, applicable also to other titanium alloys beyond Ti64.