Cryomilled Cu-Al powder and the Cu/Al mixture were sprayed onto aluminum substrate using the cold spraying process. This study focused on the wear properties of the nanocrystalline (NC) Cu-Al coating in comparison to its coarse-grained (CG) Cu/Al counterpart. The results showed that the as-sprayed deposit presented a dense microstructure. Investigations on the worn surface of the NC coating revealed that the plastic deformation with grooves and some debris were prominent with no visible cracking. Nanocrystalline Cu-Al coating showed a good wear resistance with a low friction coefficient. The enhancement of the wear properties of the NC Cu-Al was attributed to the grain refinement and the superior hardness.

It has been widely demonstrated that the bonding between particles in cold-sprayed coatings results from impact-induced extensive deformation in the interfacial area. However, the mechanism of bonding remains obscure. This present work provides theoretical and experimental evidence of localized interatomic bonds between particles. The chemical bonding energy differences between Me-O (bonding energy of metallic and oxygen atoms) and Me-Me (bonding energy of metallic atoms) indicate a preferential trend of breaking down of Me-Me bonds and therefore a new interatomic bond was established. This hypothesis is addressed in terms of dynamics based on data generated by numerical modeling. In addition, interfacial regions of cold-sprayed nanocrystalline composite coatings were observed by TEM. The results revealed that whether or not recrystallization occurred in these places was determined by development of metallic bonding between particles.