Ni-Ti(-Cu) shape memory alloy interlayers supporting low friction functional coatings

The effects of Ni-Ti(-Cu) interlayers on the mechanical and tribological behaviour of W-S-C/Ni-Ti(-Cu) and W:DLC/Ni-Ti(-Cu) bilayer coatings have been investigated. The mechanical properties of the bilayers, measured at different depths by nanoindentation, exhibited a clear dependence on the combination between different Ni-Ti(-Cu) interlayers and top layers. The tribological performance of the bilayers was evaluated by pin-on-disk under different load conditions. The use of Ni-Ti(-Cu) interlayers improved the adhesion of the top layers and the resistance against surface damage such as delamination and cracking. Transmission electron microscopy analyses performed in the wear tracks of W-S-C/Ni-Ti and W:DLC/Ni-Ti bilayers tested with high load revealed that the formation of stabilised martensite was limited when a much harder top functional layer was employed.