Friction and wear performance of hydrogenated diamond-like coatings with non-metal element complex dopants against alumina in ambient air

Abstract

Diamond-like carbon coatings (DLCs) doped with non-metallic elements were deposited onto the surfaces of 316 L steel and silicon wafer substrates using plasma-enhanced chemical vapor deposition (PECVD) by controlling the working gas. Their microstructures and chemical bonding structures were characterized using scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The mechanical properties were investigated using a residual stress tester and nano-indenter. Pin-on-ball sliding tests against Al2O3 balls were performed on the coated 316 L specimens in ambient air. A phenomenological model of the friction behavior of DLCs was proposed. It was found that during friction, the surface material removal rate was mainly determined by the stiffness of the sp3C skeleton network. A high sp3C fraction is beneficial for reducing the removal rate. The DLCs doped with a trace of nitrogen had approximately the same sp3C fraction and wear rate as a-C:H films. Contrarily, the addition of Si and O elements reduced the sp3C fraction greatly and promoted surface material removal during friction. The CN, Si–N, and Si–O bonds in DLCs can pin and protect the sp2C-rich clusters from removal by dispersion-strengthening. Si/O binary dopants are helpful for the formation of a steady tribo-layer adhered to the counter-body ball surface to achieve a low coefficient of friction (CoF); however, Si/O/N tertiary dopants are degradable. In this study, pure a-C:H and DLC with trace amounts of nitrogen exhibited a minimum wear rate (1.2 × 10−16 m3/N m), while DLC doped with 9.14 at% Si and 3.51 at% O exhibited the minimum CoF value of 0.05.