Tribological behavior of WC-Co HVAF-sprayed composite coatings modified by nano-sized TiC addition

The method of improving the properties of WC-Co thermally sprayed coatings by addition of nanostructured reinforcement for mechanical strengthening was explored in this research. Nanostructured WC-Co coatings were characterized by higher hardness than commercial counterparts, but wear tests in the literature have shown contrasting results, whereas bimodal coatings, where nanostructured components are mixed with conventional, micrometer-sized WC grains, exhibited enhanced abrasive and friction wear resistance, in comparison to coatings obtained exclusively from nano-sized powders. A mixed effect of matrix reinforcement by nanoparticles and strong fixing of the micron-sized WC grains was proposed as a possible reason for the enhanced wear resistance of bimodal coatings. A conventional, agglomerated and sintered WC-Co (83-17) feedstock powder was therefore blended with nano-sized TiC (40–100 nm) particles to obtain multimodal coatings containing a nanostructured reinforcement. The amount of TiC added into the powder mixture was in the range of 1–7 wt%. Powder mixtures were deposited onto carbon steel substrate using a High Velocity Air Fuel (HVAF) process. The dry sliding tribological behavior of the coatings was evaluated via ball-on-disk tests against Al2O3 counterparts. The tests were performed at room temperature as well as at 400 °C, with a sliding speed of 0.1 m/s, a sliding distance of 5000 m and a normal force of 10 N. The wear rates of the coatings and of the Al2O3 counterparts were measured separately, and friction coefficients were recorded during each test. The influence of TiC nano-particles on the sliding wear mechanisms was discussed in this work, based on an analysis of wear scars and wear debris through SEM + EDX and micro-Raman spectroscopy.