Microstructure and dry sliding wear behaviour of titania and alumina–titania coatings

The microstructure, hardness and wear properties of atmospheric plasma spray coating of TiO₂ and Al₂O₃–13TiO₂ with incremental hydrogen fractions (11·1–23·8%) in primary gas have been investigated in this work. TiO₂ coating shows a fine bead-like surface structure, while Al₂O₃–13TiO₂ predominantly exhibits a splat-like morphology. The microstructure shows a slight refinement in the structure for the highest hydrogen content possibly due to the higher specific enthalpy of the plasma plume. Both coatings show the highest hardness for samples coated with the highest hydrogen content possibly due to the refined structure. The roughness shows a mild decreasing trend for TiO₂ coating, while the reverse trend is observed for Al₂O₃–13TiO₂ coating. The wear loss and friction coefficient show a flat trend (0·4–0·6) for all the hydrogen contents. The worn tracks show a compacted mixture of ceramic, graphite and metallic particles.