Wear behavior of B4C–Mo co-sputtered wear coatings

Coatings of boron carbide (B4C) and B4C–Molybdenum (Mo) were co-deposited using magnetron sputtering, both with and without bias-assist. Coatings were indented using a Rockwell C Brale indenter to enable a ranking of the relative coating–substrate interfacial toughness and cracking mode. It was observed that co-sputtered B4C–Mo coatings fabricated with a higher atomic percentage (at.%) of metal and with bias exhibited the smallest cracking diameters around the indent and a less-severe cracking mode (circumferential cracking). Reciprocating sliding wear tests were performed on the coatings using a tungsten carbide–cobalt (WC–Co) ball. As for the indentation test results, lowest wear factors were calculated for bias co-sputtered B4C and high at.% Mo coatings. In addition, very mild wear damage and only occasional wear debris were observed after the wear test of the best bias co-sputtered B4C–49 at.% Mo coating. Correlations between cracking diameters from indentation and calculated wear factors were made, with lower wear factors for coatings with smaller indentation-induced cracking (i.e. higher toughness). It was observed that the application of bias during sputtering had a more beneficial effect on tribological performance than the addition of Mo, but the synergistic effect of both processing variables resulted in coatings with the best overall performance.