Molecular dynamics simulation of the residual stresses within diamond-like carbon films on iron substrates

Diamond-like carbon (DLC) films are highly desirable for application in mechanical engineering owing to their outstanding physicochemical properties. However, despite their advantages, the residual stresses generated within DLC films during deposition cause delamination of the films and limit their application to sliding components, e.g., in automobiles. In this study, through molecular dynamics simulations of the DLC film formation process due to C atom deposition on an Fe substrate, we clarified the stress evolution and spatial distribution change of sp2 and sp3 hybridized carbon bonds within the DLC film. When the C atoms started to be deposited on the Fe substrate, they penetrated the substrate surface and destroyed the body-centered cubic structure of the Fe substrate, resulting in the formation of a mixed Fe-C layer with an in-plane normal tensile stress. With further C deposition, an amorphous C layer formed on the mixed Fe-C layer. In the amorphous C layer, a considerably higher in-plane compressive stress was generated compared to that within the film on the C-Diamond substrate. This high compressive stress was attributed to the enhanced nucleation and accelerated growth of sp3 clusters due to the Fe atoms dispersed within the amorphous C layer. The clarified mechanisms of high compressive stress generation within the DLC films should be critical insights for applying these films to engineered sliding components.