Tribological properties of selected ceramic coatings

The paper presents the characteristics of some ceramic coatings obtained by a plasma spray method. The ceramic coatings Al2O3, Cr2O3 and Cr2O3+5% TiO2 were evaluated. Also the influence of the NiCr interlayer on the functional properties of sprayed coatings was studied. Other parameters studied included: thickness; microhardness; adhesion of the coatings; resistance to abrasive wear and thermal cyclic loading. The addition of TiO2 to the Cr2O3 material increased the coating density, but did not substantially reduce the hardness. On the other hand, the lowest loss of material thickness was seen for Cr2O3; while the Al2O3 and the Cr2O3+5 wt.% TiO2 material showed a higher loss. The loss in the case of the latter two was about the same. Relatively, higher values of abrasive wear resistance were observed in the Cr2O3 coatings, as compared to the reference material (Al2O3 coating), and the highest microhardness values were measured in the Cr2O3 coating. Finally, the metal interlayers in all coatings increased their resistance to thermal shock. All the coatings, using the interlayer to reduce differences in coefficients of thermal expansion, were suitable for the purpose of the thermal loading up to 1000 degrees C.