Performance of chromium nitride based coatings under plastic processing conditions

Chromium nitride based coatings were produced in the form of monolithic and multilayer coatings, by DC and RF reactive magnetron sputtering. These coa tings were deposited onto stainless steel and tool steel substrates. Chromi um nitride coatings have proved to be wear and corrosion resistant. The com bination of these characteristics was necessary to protect surfaces during plastic processing. In order to select the best coatings, some mechanical a nd tribological tests were performed. Hardness and Young's modulus of the p roduced coatings were measured by nano-indentation, adhesion was assessed b y scratch test experiments and wear was evaluated by performing pin-on-disc experiments. The behaviour of these coatings in chemically aggressive envi ronments was studied by different corrosion experiments. The behaviour of t hese coatings in thermoplastic processing equipment was also studied. The a brasive and corrosive wear of chromium nitride based coatings was assessed under relatively high pressures and temperatures and was compared with the surface wear of hardened tool steel substrate by heat treatment, nitrided b y chemical-heat treatment, or protected by hard chromium coating deposited in a galvanic way. Monolithic coatings were harder, and had higher Young mo dulus and adhesion when compared with multilayered coatings. Their wear res istance, measured by pin-on-disc test, was between two and three orders of magnitude higher, but multilayer coatings showed significantly better corro sion resistance. In general, monolithic and multilayer coatings have signif icantly better behaviour when compared with traditional processes of protec ting functional surfaces for plastic transformation equipment. The measured wear of the best performance obtained by chromium nitride based coatings c an be more than two orders of magnitude lower than nitrided surfaces or har d chromium coated samples. (C) 2000 Elsevier Science B.V. All rights reserv ed.