Strengthening mechanism of metallic nanoscale multilayer with negative enthalpy of mixing

Unlike sharp interfaces usually formed in multilayer thin films with positive enthalpy of mixing, intermixing at interface due to negative enthalpy of mixing can reduce the effectiveness of the interface as dislocation motion barrier and thus weaken the hardness/strength of the multilayer thin film. Through first-principles calculations, however, we find that the large negative enthalpy of mixing may lead to negative interface energy and thus the formation of intermetallic compounds in the interface. The resulting intermetallic compounds may have much higher shear moduli than those of the constituent metals, which can make positive contribution to the hardness enhancement of the nanoscale multilayer thin film. (C) 2011 American Institute of Physics. [doi:10.1063/1.3646560]