Wear resistant coatings: Silica sol-gel reinforced with carbon nanotubes

Pin-on-disc wear experiments have been carried out on sol-gel silica coatings reinforced with 0.1 wt.% carbon nanotubes (CNTs) deposited on WE54 magnesium alloy substrates by the dip-coating technique. Sol-gel solutions were fabricated using two different procedures: mechanical mixing (MM) and ultrasonic probe mixing. Dry sliding wear tests have been carried out at load of 1 N, speed of 0.1 m/s and sliding distance of 60 m. Friction coefficients were obtained from the tests and the specific wear rates (k) were calculated. The fabrication procedure of the coating influences its morphology and wear resistance. Friction coefficient was found to vary slightly with the addition of the CNTs. The wear volume of the magnesium substrate coated decreased by 40% and 80%, in terms of k, by using unreinforced and CNT-reinforced MM coatings, respectively. In MM layers reinforced with CNT uniform dispersion of the nanotubes was reached and toughening of the ceramic coating by pull-out and crack bridging mechanisms was observed.