Molecular dynamics study on major factors determining delamination mechanisms in diamond-like carbon films

Diamond-like carbon (DLC) films exhibit outstanding properties, including high hardness, excellent wear resistance, and low friction. However, their poor adhesion to substrates remains a significant challenge. While high compressive residual stress in the film is widely believed to weaken adhesion, the primary factors governing delamination initiation are still not well understood. In this study, we performed molecular dynamics simulations to investigate the key factors affecting the delamination strength and to clarify the underlying mechanisms. First, the deposition process of the DLC film was simulated on Fe-BCC and C-diamond substrates to prepare the DLC-coated substrate systems. Then, for these DLC-coated substrate systems, the adhesion strength was quantified according to the separation energy needed to create free surfaces at the interface. Additionally, tensile simulations were conducted to analyze the detachment behavior of the DLC-coated substrate system. The simulation results revealed that as the average compressive residual stress in the film increased, the separation energy at the film–substrate interface decreased linearly. Moreover, the separation energy, which was computed at various position from the film–substrate interface, exhibited a minimum value just above the interface due to the presence of porosity. Tensile simulations confirmed that delamination initiated at the lowest-separation energy regions, occurring earlier on Fe-BCC substrates compared with C-diamond substrates. Residual compressive stress facilitates delamination by reducing the overall separation energy, as the atomic bonds expand normal to the interface owing to Poisson's lateral strain. These findings clarify the effects of the substrate materials and deposition conditions on DLC-film adhesion and provide guidelines for increasing adhesion strength.