THE THERMAL SHOCK ENDURANCE OF A PLASMA SPRAYED ZrO₂ COATING ON STEEL

Abstract

By addition of a Ni-Cr undercoating to a steel substrate, a ZrO₂; coating with high thermal shock endurance was produced. This coating resists to an initial quenching temperature gradient of 1000 K. The plasma spray coating material is 7wt%-CaO stabilized ZrO₂ powder. The chemical composition and the thermal expansion coefficient of the base steel, and also the Ni-Cr undercoating were evaluated for thermal shock endurance. The thermal shock endurance of the ZrO₂ coatings is enhanced by the (Cr+Co) contents in the steels and by applying a Ni-Cr undercoating. The thermal expansivities of the steels have little influence on the thermal shock endurance. The carbon in the steels deteriorates the bonding of the Ni-Cr undercoating, but does not influence the ZrO₂ coatings themselves.