Cu and Cu-MoS 2 coatings were fabricated by cold gas dynamic spray and the fretting wear performance of the two coatings was compared. A mixture (95 wt.% Cu + 5 wt.% MoS 2 ) was used as feedstock for the composite coating. Coatings were sprayed with identical gas flow conditions on the substrates preheated to approximately 170°C. The cross section of the coatings was analyzed by scanning electron microscope (SEM) and MoS 2 concentration was measured, as well as coating microhardness. Fretting tests were carried out under gross slip conditions in ambient environment. SEM observation on wear scars and counterspheres revealed the development of third bodies, by which the sliding was accommodated. For the Cu-MoS 2 coating, solid lubrication effects in the form of friction drops occurred in early cycles (< 5k), but eventually (> 5k) the coating's friction behavior was similar to the pure Cu coating. Third body morphology and wear of the two coatings were distinctly different, which could largely be attributed to the hardness reduction of the Cu-MoS 2 composite due to poorly bonded interfaces induced by the effect of MoS 2 during particle impact and coating formation.

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.