Role of Characteristic Length Scale in Interface Graphitization-Induced Wear Resistance of Diamond and Amorphous Carbon

Abstract

The evolution of interfacial atomic structures critically influences the friction and wear behavior of carbon-based materials. However, how the characteristic length scale of friction-induced sp\textsuperscript{2} reconstruction governs macroscopic wear remains poorly understood, particularly for diamond and amorphous carbon where the interfacial graphitization modes differ fundamentally. In this work, we develop a machine learning potential for these carbon systems and investigate the structural evolution at interfaces in both diamond/diamond and amorphous/amorphous carbon systems using molecular dynamics simulations. Our results reveal distinct atomic-scale characteristics of graphitization at the two interfaces. Diamond interfaces develop a laterally continuous sp\textsuperscript{2} reconstruction layer with a characteristic length of 30--45~Å, while amorphous carbon interfaces form only fully isolated sp\textsuperscript{2} patches of 8--12~Å. This disparity in characteristic length scale determines the density of weakly bonded interfacial atoms left outside the reconstruction layer, thereby directly dictating the macroscopic wear rate. Based on these insights, we propose a strategy to regulate friction-induced graphitization in diamond coatings by protecting specific crystallographic orientations, such as the (111) close-packed planes. This work bridges the gap between atomic-scale interfacial structure and macroscopic tribological performance, offering mechanistic guidelines for the rational design of wear-resistant carbon-based coatings.