Engineering titanium alloys for additive manufacturing: Feedstock design, solidification control, and functional properties

There are thousands of different metallic alloys, but only a few have been officially certified for use in laser powder bed fusion (L-PBF). This is a primary reason why the range of available materials in metal Additive Manufacturing (AM) remains somewhat limited. This review focuses on in-situ alloying combined with fusion-based additive manufacturing processes, specifically titanium (Ti) alloys produced by L-PBF and electron beam powder bed fusion, with laser-directed energy deposition included for comparison. The discussion first addresses the feedstock stage, including powder characteristics, thermophysical mismatches between blended constituents, composition homogeneity, and preparation routes such as conventional blending, MA, satellite milling, and coating. It then links these feedstock conditions to melt-pool transport and solidification, where elemental dissolution, Marangoni-driven mixing, segregation, growth restriction, columnar-to-equiaxed transition, and phase selection are controlled by scan strategy and energy input. Defect formation is also considered within powder bed fusion processing windows, with attention to lack of fusion, keyhole porosity, spatter, denudation, powder-bed instability, and powder-related contamination. The review further compares the microstructural and property responses of major in-situ Ti alloy systems. Multicomponent systems show that the most useful property combinations are obtained when alloy chemistry, feedstock architecture, melt-pool mixing, solidification path, and post-build transformations are treated as a coupled design problem. Up to now, in-situ alloying has proved effective for expanding the Ti alloy design space beyond fixed pre-alloyed powders, but its wider use is still limited by compositional instability, incomplete dissolution, process-window sensitivity, property scatter, and qualification barriers. Further work should therefore focus on validated powder specifications, closed-loop monitoring of melt-pool stability and composition, physics-based modelling linked with non-destructive evaluation, and scalable standards that can move in-situ Ti alloying from laboratory alloy development toward reproducible industrial AM production.