A comprehensive investigation into microstructure evolution of the diamond-like carbon anchored into hardening layer with nano-carbonitrides

Diamond-like carbon (DLC) film is an effective solid lubricant for M50 steel to improve its tribological performance. A functional layer was prepared on pre-nitrided M50 steel via plasma carburizing, in which a diamond-like carbon (DLC) film is anchored into the hardening layer containing nano-carbonitrides. The evolution of the functional layer’s structure and performance was systematically investigated using optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), micro-Vickers hardness testing, and friction and wear testing. It was found that the microstructure and mechanical properties of the self-lubricating functional layer exhibit a pronounced dependence on carburizing duration. The short-term carburized specimen exhibits the highest surface hardness and the lowest volumetric wear rate. As the carburizing time increases, a serrated interface gradually forms between the DLC film and the dense compound layer, attributed to the synergistic effects of interstitial atom diffusion and compound transformation. The evolutionary mechanisms of the integrated functional layer were systematically analyzed using first-principles calculations and growth kinetics modeling to provide a fundamental basis for the industrial application of diamond-like carbon (DLC) in aerospace bearing systems.