Effects of sp³ bond and modulation ratios on ultra-thin diamond-like carbon coatings using molecular dynamics nanoindentation

CD Wu and NY Yeh, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 129, 839 (2023).

DOI: 10.1007/s00339-023-07127-6

Diamond-like carbon (DLC) films, which are generally used in the form of protective coatings, have a lot of engineering applications, where they improve surface friction, adhesion, and wear resistance. Hence, it is necessary to understand the correlation between DLC coating parameters and the mechanical properties. The effects of sp(3) bond and modulation ratios of DLC coatings on the deformation and mechanical properties are studied using molecular dynamics (MD) nanoindentation simulations. MD simulations allow the analyses of the mechanical deformation and mechanics of nanosystems. The in situ material degradation and local deformation of DLC coatings are examined during nanoindentation. The simulation results show that single-layer DLC with a higher initial sp(3) ratio generally has a larger indentation force (higher resistance to indentation), a smaller influence area, and a larger residual depth after unloading. With an increase in initial sp(3) ratio, the sp(3)-sp(2) bonding transition of C atoms significantly increases at stages of loading, holding, and unloading. Amorphous carbon/tetrahedral amorphous carbon (a-C/ta-C) bilayers with a smaller modulation ratio and ta-C/a-C bilayers with a larger modulation ratio generally require a larger indentation force. Bilayers have poor overall support when the soft (a-C) layer is the bottom layer, which increases the influence area.

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