XPS STUDY OF THE ADHERENCE OF REFRACTORY CARBIDE, SILICIDE, AND BORIDE RF-SPUTTERED WEAR-RESISTANT COATINGS

Radio frequency sputtering was used to deposit refractory carbide, silicide, and boride coatings on 440-C steel substrates. Both sputter etched and pre-oxidized substrates were used and the films were deposited with and without a substrate bias. The composition of the coatings was determined as a function of depth by x-ray photoelectron spectroscopy combined with argon ion etching. Friction and wear tests were conducted to evaluate coating adherence. In the interfacial region there was evidence that bias may produce a graded interface for some compounds. Biasing, while generally improving bulk film stoichiometry, can adversely affect adherence by removing interfacial oxide layers. in all cases but the iron oxide coverage was only complete on the preoxidized substrates. The film and iron oxides were mixed in the MoSi//2 and Mo//2C films but layered in the Mo//2B//5 films. In the case of mixed oxides, pre-oxidation enhanced film adherence.