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.