The cold-gas dynamic-spray process is analyzed by numerical modeling of the impact between a single spherical feed-powder particle and a semi-infinite substrate. The numerical modeling approach is applied to the copper-aluminum system to help explain experimentally observed higher deposition efficiencies of the copper deposition on aluminum than the ones associated with the aluminum deposition on copper. To properly account for the high strain, high strain-rate deformation behavior of the two materials, the appropriate linear-elastic rate-dependent, temperature-dependent, strain-hardening materials constitutive models are used. The results obtained indicate that the two main factors contributing to the observed higher deposition efficiency in the case of copper deposition on aluminum are larger particle/substrate interfacial area and higher contact pressures. Both of these are the result of a larger kinetic energy associated with a heavier copper feed-powder particle. The character of the dominant particle/substrate bonding mechanism is also discussed in the present paper. It is argued that an interfacial instability which can lead to the formation of interfacial roll-ups and vortices can play a significant role in attaining the high strength of interfacial bonding. (C) 2003 Elsevier Science B.V. All rights reserved.