In-situ alloying of Ti-Nb-Sn samples by Laser Additive Manufacturing: Phase stability and non-isothermal heat treatment

Powder bed fusion - laser beam (PBF-LB) typically relies on pre-alloyed metallic powders, allowing for precise control over their composition, morphology, and particle size, which are achieved through advanced atomization methods. In-situ alloying in PBF-LB presents a cost-effective solution for developing non-commercial alloys, avoiding complex and costly pre-alloying procedures. One critical aspect to consider when employing in-situ alloying in PBF-LB is achieving microstructure homogenization, which can be influenced by the presence of elemental particles and uneven distribution of alloying elements. In this work, a Ti-30Nb-2.5Sn (wt.%) alloy was produced by PBF-LB using elemental powder blends under two representative processing conditions to elucidate process-microstructure–property relationships. Processing with low laser power and high scanning speed resulted in chemically heterogeneous microstructures containing unmelted Nb particles. These particles locally stabilized the β phase, induced microstructural gradients, and promoted ω -phase precipitation. In contrast, optimized processing conditions yielded a more homogeneous microstructure with columnar prior- β grains and reduced ω -phase formation. The optimized condition exhibited a high as-built ultimate compressive strength of approximately 1303 ± 117 MPa, exceeding values reported for cast Ti-Nb-Sn alloys. Differential scanning calorimetry revealed overlapping transformation events consistent with the β → ω i s o → β 0 → α sequence, with reduced thermal activity upon reheating, indicating partial completion of phase transformations. After DSC thermal cycling, only α and β phases were detected. A systematic gradient in α -plate thickness developed during heat treatment and was attributed to differential oxygen uptake, demonstrating a potential pathway for spatial control of microstructure and mechanical properties. This effect was suppressed in samples containing unmelted Nb particles due to strong local β -phase stabilization. These findings highlight the critical role of processing parameters in controlling Nb dissolution, phase stability, and microstructural uniformity in in-situ alloyed Ti–Nb–Sn systems processed by PBF-LB. • Ti-30Nb-2.5Sn alloy produced by PBF-LB using in-situ alloying of elemental powders. • In-situ alloying removed the need for pre-alloyed powder feedstock. • Process parameters strongly influenced Nb dissolution and microstructural uniformity. • Low energy density caused undissolved Nb particles and local phase instability. • Optimized conditions led to columnar prior- β , suppressed ω -phase, and high strength.