Annealing-induced microstructural and corrosion behavior of a novel Ti–5Cu–1Si alloy processed via laser powder bed fusion process

Abstract In the present work, a novel Ti–5Cu–1Si alloy was developed via laser powder bed fusion (L-PBF) using the in-situ alloying approach. The alloy was then subjected to annealing heat treatments at 700, 850, and 1100°C, followed by controlled, slow furnace cooling. Subsequently, the impact of the annealing treatment on the microstructure and corrosion resistance of this alloy was studied. The results demonstrated that annealing of the LPBFed Ti–5Cu–1Si alloy at 700, 850, and 1100 °C temperatures promoted the formation of α -Ti, Ti 2 Cu, and Ti 5 Si 3 phases, along with a decrease in the compositional disparity between the α phase and the Ti matrix attributable to the depletion of the non-equilibrium acicular α’ -Ti phase from the supersaturated Cu and Si elements. When heated at 1100 °C, the average i corr value decreased from 0.86 to 0.33 µA, and the average E corr value increased from − 0.223 to − 0.215V. This trend is attributed to the transformation of the non-equilibrium α’ phase into the eutectoid mixture of α -Ti+Ti 2 Cu+Ti 5 Si 3 , reduced lattice microstrain, lesser compositional difference between the α -Ti phase and the Ti matrix, and the increased microstructural homogeneity. Annealing at 850 °C further enhanced the corrosion resistance of the alloy, increasing the average E corr value to − 0.141 V and decreasing the average i corr value to 0.1 µA. Annealing at 700 °C resulted in an average E corr value almost identical to that of the sample annealed at 850 °C (− 0.165 V), although the average i corr value was 0.32 µA. The attribution lies in the reduced sizes of β grains and the α phase, coupled with more evenly distributed Ti 2 Cu and Ti 5 Si 3 intermetallic precipitates in the LPBF-produced Ti–5Cu–1Si alloy microstructure after annealing at 700 and 850 °C, relative to those at 1100 °C. In addition, a significant increase in the passive film resistance ( R p ) values was observed after annealing at 850 °C, rising from 0.068877 to 70.736 MΩ. cm 2 . This was related to the protective effect of the Ti2Cu and Ti5Si3 intermetallic phases, which shielded the α’/α-Ti, as well as the presence of smaller, equiaxed prior β grains and reduced spacing between Ti 2 Cu and Ti 5 Si 3 precipitates. The improved corrosion behavior of the alloy after annealing at 850 °C, compared to other Ti–Cu-based alloys produced by L-PBF and casting processes reported in previous studies, suggests that it could be a suitable candidate for biomedical applications.