Particle temperature effect in cold spray: A study of soft particle deposition on hard substrate

In cold spray, the interactions between feedstock particles and propellant gas control deposition outcome. The particle impact temperature, along with impact velocity, governs the deposition due to its effect on the impact deformation processes. As bonding mechanisms rely primarily on the particle/substrate plastic flow upon impact, particle impact temperature holds a predominant role in process optimization. The current work studies the effect of pure aluminum particle impact temperature on deposition phenomena when propelled onto a hard steel substrate. Particle impact temperature was varied while achieving the same particle impact velocity, using low and high-pressure cold spray systems. Three different particle diameters are studied, with varying resulting inherent impact temperatures, to provide size dependent insight on deposition/adhesion. Experimental results demonstrate that at low particle impact temperature, i.e. 50 °C, coating adhesion is controlled by in-situ peening. Adhesion shifts to particle in-flight characteristics dependent bonding, i.e. η = V/Vc, as particle temperature increases. At low particle impact temperatures, the coating bond strength increases with increasing in-situ impingement intensity and frequency, i.e. decreasing deposition efficiency with increasing particle size. At higher particle impact temperatures, in-situ peening rate decreases and the adhesion strength increases with decreasing particle size. In addition to affecting the impact process (DE, Vc and adhesion), the particle impact temperature also influences the coating mechanical properties through the creation of temperature-dependent crack propagation mechanisms, i.e. deflection, bridging and acceleration, and of particle-particle structural arrangement related to deformation processes, i.e. fish scale effect and pseudo-plasticity behavior.