Deposition behavior of thermally softened copper particles in cold spraying

Finite-element analysis (FEA) combined with experimental observation was conducted on preheated Cu particles deposited on Cu substrate to clarify the deposition behavior of thermally softened particles in cold spraying. An explicit FEA code, ABAQUS, was used to predict the deformation features of the thermally softened particles. The experiment was performed by a home-made cold-spray system with a powder preheating device. Considering the possible serious oxidation of the cold-sprayed particles under high-temperature conditions, the preheating temperature was limited to 300 °C for each test. Based on the numerical and experimental results, a new concept called the thermal softening zone within which thermal softening occurs is proposed in the present work. It is found that thermally softened particles deform more intensively compared to non-preheated particles, and a more prominent metal jet can be achieved at the rim of the deformed particles with higher initial temperature. Moreover, the results also reveal that increasing the particle preheating temperature can stimulate the occurrence of thermal softening. For non-preheating or low-temperature preheating particles, thermal softening mainly occurs at the interfacial region. If the preheating temperature is sufficiently high, the whole particle can experience thermal softening. In addition, it is also found that preheated particles are more likely to deposit on the substrate surface than non-preheated particles. In addition, particle preheating is also found to facilitate the coating formation process, enabling the coating to be very thick. The coating microhardness decreases with increasing particle preheating temperature due to the elimination of work hardening by thermal softening.