Influence of Graphite and Zirconia Addition on the Tribological Properties of Plasma-Sprayed Alumina Coatings

Al₂O₃, Al₂O₃-graphite and Al₂O₃-ZrO₂ coatings were formed on the C45 steel rolls using atmospheric plasma spraying. The influence of graphite and zirconia addition on the surface morphology, phase composition and tribological properties under dry sliding conditions using 30 N load were analyzed. It was found that the addition of graphite or ZrO₂ slightly affected the fraction of the α-Al₂O₃ and γ-Al₂O₃ phases in the alumina coatings. The highest mass loss rate (~8.84 × 10⁻⁴ g/s) was obtained for the friction pair of C45 steel roll and steel plate. The friction coefficient of the Al₂O₃-graphite coating was slightly lower (up to 7%) compared to the coating of Al₂O₃-ZrO₂. However, the friction pair of Al₂O₃-ZrO₂ coating and steel plate demonstrated the highest wear resistance under dry sliding conditions. The increase in the wear resistance of the Al₂O₃-graphite and Al₂O₃-ZrO₂ coatings is due to the formation of tribofilm in the sliding contact zone.