Microstructure and tribomechanical properties of (Cr, N)-DLC/DLC multilayer films deposited by a combination of filtered and direct cathodic vacuum arcs

Alternating multilayer diamond-like carbon (DLC) films [(Cr, N)-DLC/DLC] with different sp(3) contents in DLC layer have been prepared on YG8 (WC-Co) substrates by FCVA combined with DCVA technique. The structure was investigated by scanning electron microscopy and transmission electron microscopy. Chemical bonding was studied by Raman spectroscopy and X-ray photoelectron spectroscopy. Mechanical and tribological properties including residual stress, hardness, adhesion strength and wear resistance were evaluated by film stress tester, nanoindenter, scratch tester, ball-on-disk tribometer and surface profiler. The results showed that (Cr, N)-DLC layer had the composite structure of amorphous phase as base interspersed with a small amount of nano-crystals. The co-doping of Cr and N into DLC reduced the film's residual stress from -1.62 GPa to -0.99 GPa. For monolayer DLC, both the sp(3) content and residual stress decreased as the substrate's bias voltage increased in the range of -100 V to -600 V. And the decrease of sp(3) content contributed to an increase of the (Cr, N)-DLC/DLC films' toughness. In addition, the multilayer films presented good adhesion strength on YG8 substrates. The wear rates of all multilayer films belonged to the order of magnitude of 10(-7) mm(3)/Nm. Prime novelty statement: Multilayer films consisting of DLC and DLC co-doped with metal and nonmetal atoms [(Cr, N)-DLC/DLC multilayer films] have been prepared by FCVA combined with DCVA technique and investigated systematically. The composite structure of the (Cr, N)-DLC layer is based on amorphous phase and contains a small number of nano-crystalline compounds of chromium. (C) 2015 Elsevier B.V. All rights reserved.