Study of the influence of microstructural properties on the sliding-wear behavior of HVOF and HVAF sprayed WC-cermet coatings

The microstructural properties of WC-Co-Cr and WC-Co coatings deposited by high-velocity oxygen fuel (HVOF) and high-velocity air fuel (HVAF) processe s were investigated. The tribological behavior of the coatings was studied by means of pin-on-disk tests. Microcracking of the HVOF sprayed WC-Co coat ings did not allow preparation of suitable disks for wear tests. The wear r ates of the remaining coatings were determined, and wear tracks on the coat ings and counterbodies were investigated by SEM, The HVAF sprayed coatings showed greater sliding-wear resistance compared to the HVOF coatings. The p rime wear mechanism in the WC-Co HVAF coatings was adhesive wear. The cobal t matrix is lubricious, resulting in very low wear rates and low debris gen eration. The main wear mechanisms in the WC-Co-Cr coatings were adhesive an d abrasive wear. Adhesive wear results in coating material dislodgments (i. e., "pullouts") that become trapped in the contact zone and act as a third- body abrasive. Particle pullout from the coating significantly increases th e wear rate of the coated specimen. The HVAF/WC-Co-Cr coatings exhibited be tter resistance to particle pullout, resulting in a considerably lower wear rate than the HVOF/WC-Co-Cr coatings.