Design and optimization of rectangular cold spray nozzle: Radial injection angle, expansion ratio and traverse speed

A cold spray nozzle with radially injected powder was numerically modeled and experimentally validated. The gas flow field and particle trajectories were simulated for various injection angles and expansion ratios. Injection angle was seen to affect particle distribution and injection pressures. The effect of expansion ratio was numerically studied and experimentally verified with stainless steel powders. For this material system, highest deposition efficiency was observed at an overexpanded flow regime. High deposition rate was accompanied by strain rate induced phase change. In addition, the effect of traverse speed (between 1 and 6 mm/s) was assessed experimentally. While the speed did not affect bond strength and coating hardness, an optimum speed was found where there was a substantial increase in deposition rate.