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

Abstract

Alternating multilayer diamond-like carbon (DLC) films [(Cr, N)-DLC/DLC] with different sp3 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 −1.62GPa to −0.99GPa. For monolayer DLC, both the sp3 content and residual stress decreased as the substrate's bias voltage increased in the range of −100V to −600V. And the decrease of sp3 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 10−7mm3/Nm. Prime novelty statementMultilayer 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.