Novel load-carrying layers to support low-friction PVD coatings

Five different materials have been studied with respect to their load-carrying capacity together with PVD coatings. The materials were mild carbon steel, hardened and annealed ball bearing steel, a thick electro-deposited Ni coating, and plasma-sprayed alumina coatings with and without the pores and cracks sealed with electro-deposited Ni. The two latter materials have not previously been studied in this respect. A WC-doped hydrogenated diamond-like carbon (Me-C:H) coating was deposited on each material. All materials were subjected to mechanical and tribological testing, including scratching, nanoindentation and pin-on-disc testing. The sealed plasma-sprayed alumina coating, as well as the unsealed, behaved surprisingly well as load carriers for PVD coatings, despite their porosity and low cohesion. The overall trend was that hard materials generally functioned better than soft ones. However, there is at present a small risk of chipping of the sprayed materials, which can be reduced by future process optimisation.