Thick diamond like carbon coatings deposited by deep oscillation magnetron sputtering

Hydrogenated diamond like carbon (DLC) coatings with thicknesses up to 20 μm have been deposited on metal substrates by sputtering a graphite target in argon (Ar) and acetylene (C2H2) mixture using deep oscillation magnetron sputtering (DOMS). The coatings were deposited under moderate peak target current densities (0.47 to 0.6 Acm− 2) and a low bias voltage of − 60 V, to achieve dense microstructure but avoid building up of high residual stresses. Higher peak substrate current densities and deposition rates were found when C2H2 was introduced. The effects of the C2H2 flow rate (fC2H2) on the deposition rate, microstructure, adhesion, mechanical and tribological properties of the DLC coatings were studied by means of scanning electron microscopy, Raman spectroscopy, HRC indentation, nanoindentation, dry ball-on-disk test, and block-on-ring test in SAE 10W-30 engine lubricant. The coatings showed low compressive stresses in the range of − 0.5 GPa to − 1.8 GPa. The coatings exhibited dense structure, high sp3/sp2 ratio, and excellent wear resistance when the C2H2 flow rate was in the range of 10-20 sccm (4%-8% of the total gas flow). The friction and wear behavior of the DOMS DLC coatings both in the ambient air and SAE 10W-30 engine lubricant showed positive results in terms of friction and wear reduction.