HVOF-sprayed WC-Co as hard interlayer for DLC films

This study evaluates the technical improvement achieved by applying a thick HVOF-sprayed WC-17Co interlayer between a DLC thin film and an AISI1040 steel substrate. The chemical composition (from XPS analysis) and hardness (from nano-indentation test) of the DLC films deposited on both bare and HVOF-coated AISI1040 steel are analogous. Nevertheless, the better adhesion of the DLC film on WC-17Co interlayer is demonstrated by higher critical loads recorded in scratch testing. During ball-on-disk dry sliding tribological tests, the low hardness of the AISI1040 substrate causes delamination phenomena in the DLC film. When contact pressure is low, delamination is limited, both at room temperature and at 400 °C; instead, delamination under high contact pressure is severe at room temperature and complete at 300 °C. The hard WC-17Co interlayer significantly improves the tribological performance, although delamination eventually occurs, after long sliding distances, under high contact pressure at 300 °C.