The role of surface oxides in cold spray additive manufacturing of titanium

This paper systematically investigates the interplay between particle oxidation and its strength response of Ti powder and their subsequent influences on particle deposition in cold spraying. After oxidation in air at 500 °C for 4 h, fine-sized Ti powder exhibits the highest uptake of oxygen and hydrogen among the used three powders of different size ranges, accompanied by a decrease in average particle strength from 811 to 715 MPa. Oxidation results in the formation of nano-crystalline tetragonal TiO₂ layers on particle surfaces, which act as barriers to metallic bonding during deposition. Consequently, the oxide films suppress particle deformation, as reflected by the reduced flattening ratio and bonding efficiency of oxidized particles. The results not only reveal the microstructure evolution of the bonding interface, as well as deepen the understanding of interactions between Ti powder and substrate under extreme strain-rate condition, but also highlight the necessity of controlling powder oxygen to achieve reliable microstructural integrity and performance in cold spray additive manufacturing of Ti workpieces.