Comparative tribological study of plasma sprayed alumina and alumina-yttria under severe conditions

In the current study, alumina and alumina-yttria composite coatings were prepared on stainless steel substrates via atmospheric plasma spraying. Their dry sliding wear performances against graphite under severe conditions were evaluated by using a ring-on-disk tribometer. The results showed that the addition of yttria has successfully decreased the friction coefficients of the alumina coatings. Further, the temperatures in the friction process rose sharply in the initial wear stage and then reached the state of thermal equilibrium. The temperatures of alumina-yttria coatings at thermal equilibrium stages were lower than those of alumina coatings, which may be due to their lower friction combined with the slightly higher thermal conductivity. High friction interface temperatures were considered to greatly aggravate the thermal stress, thereby intensifying the cracking of alumina coatings. Additionally, the addition of yttria improved the toughness of composite coatings and the related crack propagation resistance.