Sliding wear behavior of plasma sprayed alumina-based composite coatings against Al2O3 ball

The sliding wear behaviors of a single layer Al2O3-30 wt pct ZrO2, a double layer Al2O3-30 wt pct ZrO2/Ni-Cr and a single layer Al2O3-13 wt pct TiO2 coating deposited on low carbon steel by plasma spraying were investigated under lubricated conditions with various normal loads. The plastic deformation, detachment and pull out of splats were involved in the wear process of the studied coatings under test conditions. Crack propagation was found in Al2O3-13 wt pct TiO2 under loads of 70 and 100 N and in Al2O3-30 wt pct ZrO2/Ni-Cr under a load of 130 N. While increasing the normal load, the wear rates of Al2O3-30 wt pct ZrO2 and Al2O3-30 wt pct ZrO2/Ni-Cr slightly increased, the wear rate of Al2O3-13 wt pct TiO2 increased rapidly. The results showed that the Ni-Cr bonding layer improved the wear resistance of the coating system even it is relatively thin compared with the outer coating layer. The influence of this bonding layer on wear behavior of the coating increased as increasing the normal load.