Effect of annealing treatment on the microstructure and properties of cold-sprayed Cu coating

Copper (Cu) coating was deposited by cold spraying, and the electrical resistivity of the coating in both directions parallel and perpendicular to the coating surface was measured to investigate the anisotropy of the coating. Annealing treatment was applied to the coating to examine its effect on the microstructure and properties of the cold-sprayed Cu coating. The examination of coating microstructure evidently revealed that the coating was constituted by the flattened particles, and the interfaces were clearly observed between the deposited particles. The anisotropy in microstructure and electrical resistivity was present in cold-sprayed Cu coating. The electrical resistivity of the as-sprayed coating was higher than that of Cu bulk. Moreover, the electrical resistivity along the direction parallel to the coating surface was lower than that along the perpendicular direction. It was found that annealing treatment led to the enhancement of particle interface bonding and evident recrystallization of the elongated grains and remarkable grain growth as well. The annealed coating presented equiaxed grain structures similar to the annealed Cu bulk with particle interfaces almost disappearing under certain annealing conditions The coalescence of voids or pores in the coating was clearly observed at high annealing temperatures. Moreover, the annealed coating yielded an electrical resistivity and microhardness comparable to Cu bulk.