Unveiling Plastic Deformation Mechanisms of Diamond-Like Carbon under Nanoindentation Using Molecular Dynamics Simulation

Diamond-like carbon (DLC) is famous for its extraordinary mechanical properties in tribology applications. Despite the growing interest and achievements in exploiting more advanced DLC, unveiling the deformation mechanisms, especially in the plastic regime, remains a great challenge. Here, molecular dynamics (MD) simulation, as an <i>in situ</i> computational microscopy technique, was employed to probe the atomically structural and mechanical responses in DLC with a certain density to nanoindentation. In particular, the evolving spatial distributions of changes in shear strains, atomic displacements, hybridization states, stress tensors, and atomic clusters induced by an indenter were investigated in detail. It was found that the plasticity in DLC initiates at the fertile regions of a high free volume provided by the sp²-C sites centered on a sp³-C one and proceeds in a series of discrete atomic rearrangements involving dynamic and partially reversible transitions between any hybridization states of carbon atoms. The sp²-to-sp³-dominated transition assisted by the small-scale shear transformations in DLC can be triggered by a stress threshold lower than the yield limit or that expected before. This work provides new insights into the source and mechanisms of plasticity in DLC and potential to modify or further improve DLC in mechanics.