Laser powder bed fusion in-situ alloying for fabrication of high-performance Ti6Al4V-Fe alloys

The Laser Powder Bed Fusion (L-PBF) process, characterized by high temperature gradients and rapid cooling rates, often results in the formation of coarse columnar grains in Ti6Al4V alloy, leading to anisotropy in its mechanical properties. To optimize the solidification microstructure and mechanical performance of Ti6Al4V fabricated via L-PBF, we investigated an in-situ alloying approach within the L-PBF process. A series of novel Ti6Al4V-xFe (x = 1, 3, 5) alloys were fabricated and systematically analyzed in terms of microstructural characteristics and mechanical properties. The results demonstrate that Ti6Al4V-xFe exhibit a dual-phase microstructure, consisting of α′ and β phases, in which the volume fraction of the metastable β phase increases with the increase of Fe content. The in-situ alloying of Fe elements effectively suppresses the growth of columnar grains and promotes the Columnar-to-Equiaxed Transition (CET). Specifically, when the Fe content is 1 wt%, the alloy achieves a high strength of 1591.7 MPa, though with relatively low ductility. When the Fe content is 5 wt%, despite a reduction in strength (1204.3 MPa) compared to Ti6Al4V-1Fe, the material displays remarkable work-hardening behavior and improved ductility (with an elongation of up to 13.1 %). This enhancement in mechanical properties can be primarily attributed to the increased metastable β phase, the cooperative deformation between the phases, and the progressive Transformation-Induced Plasticity (TRIP) effect triggered by the β phase.