Preprint of journal paper "In-situ alloying of Ti-Nb-Sn samples by Laser Additive Manufacturing: phase stability and non-isothermal heat treatment"

This is a preprint of the manuscript “In-situ alloying of Ti–Nb–Sn samples by Laser Additive Manufacturing: phase stability and non-isothermal heat treatment”, currently under peer review. It has been submitted to Zenodo under the CC BY 4.0 license.

Authors

Márcio Sangali (a), João Felipe Q. Rodrigues (b), Leticia F. Starck (b), Gilberto V. Prandi (b), Matheus Valentim (b), Josef Stráský (c), Rodolfo da Silva Teixeira (b), Leandro S. Silva (d), Miloš Janeček (c), Rubens Caram (b)
(a) Instituto Federal de Educação, Ciência e Tecnologia de São Paulo (IFSP), São João da Boa Vista, SP, Brazil
(b) University of Campinas, School of Mechanical Engineering, Campinas, São Paulo, Brazil
(c) Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16, Prague, Czech Republic
(d) Instituto de Ciências Ambientais, Químicas e Farmacêuticas, Universidade Federal de São Paulo (UNIFESP), Diadema, SP, Brazil

Abstract

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 suppressed ω-phase formation. The optimized condition exhibited a high as-built ultimate compressive strength of approximately 1355 MPa, exceeding values reported for cast Ti-Nb-Sn alloys. Differential scanning calorimetry revealed overlapping transformation events consistent with the β → ωiso → β0 → 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.