Formation of metastable phases in cold-sprayed soft metallic deposit

Zinc powder was used to deposit coating by cold spraying using nitrogen as driving gas. The microstructure of the deposited coating was characterized by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results showed that the cold-sprayed Zn coating presented a dense microstructure. The nanograins formed at the interface area between deposited particles, while the size of grains in the bulk inside of the particles in the coating was comparable to that in the starting powder. The interface region of the oriented lamellar microstructure was observed. The refinement of grains to the nanocrystallines at the particle-particle interfaces is achieved through the recrystallization of elongated grains resulting from intensive deformation. The lamellar microstructure is formed by the successive deformation of deposited fine particulates resulting from the jetting of impact-induced melt. An evolution model of the interface microstructure in cold spraying is proposed.