The role of Ni-Ti-(Cu) interlayers on the mechanical properties and nano-scratch behaviour of solid lubricant W-S-C coatings

A self-lubricant W-S-C coating with different Ni-Ti-(Cu) interlayers was fabricated by magnetron sputtering following a three-step process. It consisted of deposition and annealing of Ni-Ti-(Cu) layers with different Cu contents and subsequent deposition of the transition metal dichalcogenide W-S-C coating bonded to the Ni-Ti-(Cu) layer through a gradient Cr-based thin layer. Doping the Ni-Ti interlayer with Cu led to significant microstructural changes which influenced mechanical properties, such as the H/Er ratio and the resistance against plastic deformation. The response of the bilayers, i.e. W-S-C/Ni-Ti-(Cu) coatings, to indentation was affected by the interlayer material. The resistance to adhesion damage of the W-S-C coating was improved by using Ni-Ti-(Cu) interlayers. It was found that interlayers with lower H/Er ratio showed an improved capability to increase the adhesion of the functional top layer.