Restoring the ductility of in-situ alloying additively manufactured Ti-Fe alloy via short-time heat treatment

Chemical inhomogeneity is a longstanding problem of in-situ alloying based laser powder bed fusion (LPBF), arising from an ultra-short laser irradiation time and intrinsic rapid solidification experienced in the melt pool of the printing process. As a unique kind of chemical inhomogeneity in titanium alloy, beta fleck often emerges in the microstructure of Ti-Fe alloy fabricated via in-situ alloying based LPBF, which leads to extremely low ductility of the alloy in the as-built state. To address this problem, a short-time heat treatment within a few minutes was proposed, as a result, the plastic deformation ability of the alloy is successfully recovered. The underlying mechanisms are revealed based on careful microstructure observation and deformation theory analysis. It is found that both the size and chemical concentration of the Fe segregation defect are significantly reduced by the short-time heat treatment due to fast diffusion of the iron, thus relieving the mechanical inhomogeneity and stress concentration upon deformation and restoring the plastic deformation ability of the LPBF Ti-Fe alloy. Meanwhile, at nanoscale the supersaturated Fe element dissolved in the lamellar α lattice is repartitioned to the interlamellar β phase after the short-time heat treatment, combined with widening of α lamellae, resulting in a sharp softening of the Ti-Fe alloy. The findings not only elucidate the mechanism of the ductilization effect of short-time heat treatment on the in-situ alloying fabricated Ti-Fe alloy but also provide an efficient approach to eliminate the chemical inhomogeneity of the in-situ alloying based additive manufacturing.