Effect of the methane flow ratio on the structural and mechanical properties of high-entropy alloy co-doped DLC films

High-entropy alloy is co-doped in diamond-like carbon films by sputtering using a single (AlCrNbSiTiV) target. This study analyzed the effects of methane flow rates [Rm = CH4/(Ar + CH4) flow ratio], which varied in the range from 16 to 24%, on the morphological, phase structures, mechanical characteristics and tribological behavior of diamond-like carbon films. The diamond-like carbon film is characterized using Raman spectroscopy, nano-indentation, high-resolution transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and scratch testing. As a result, the element concentration in the diamond-like carbon films is quite near to the High-entropy alloy target composition, and the metal content of co-doped diamond-like carbon films decreases as the fraction of the methane reactive gas increases. For a monotonically increasing Rm flow ratio, the position of the G-peak is downshifted to a low wavenumber, a decrease in ID/IG ratio suggests a decrease in sp2/sp3 ratio, which is associated with the decrease in the fraction of graphite and the more disordered carbon structure. An increase in the Rm flow ratio results in increased hardness (H) and elastic modulus (E) and a decreased friction coefficient, wear rate, H3/E2 and H/E. Cutting tests using a tool coated in a diamond-like carbon film shows the cutter life was extended.