In-flight aggregation and deposition behaviour of particles in low pressure cold spray

Abstract

Low pressure cold spray (LP-CS) is a kind of cold spray (CS) technology. Due to lower gas pressure, particles are difficult to deposit using LP-CS. The particles should be softened by heating of the carrier gas (200 °C–600 °C) in the Laval nozzle to compensate for this deficiency. In this study, the morphology of particles ejected from the Laval nozzle was observed using a scanning electron microscope (SEM), and the aggregation phenomenon between particles was obtained for the first time. With increasing the carrier gas temperature, the particle morphology tended to be irregular gradually due to aggregation and this phenomenon cannot be ignored. Based on this phenomenon, an aggregated particle model was established and the deposition behaviour was investigated by a coupled thermomechanical Eulerian method. The results show that the equivalent plastic strain (PEEQ) of the aggregated particle mainly depends on the particle velocity, and the change of temperature depends more on the original particle temperature. Compared with the individual particles, the bonding between the aggregated particle and substrate is poor at the middle position. In addition, the multi-particles deposition simulation indicates that the formation of coating pores could be inhibited to some extent by the phenomenon of aggregation between particles.