Thermal barrier coating life and isothermal oxidation of low-pressure plasma-sprayed bond coat alloys

Abstract

The isothermal oxidation kinetics of Ni-35Cr-6Al-0.95Y, Ni-18Cr-12Al-0.3Y and Ni-16Cr-6Al-0.3Y (composition in weight per cent) low-pressure plasma-sprayed bond coat alloys were investigated and the effect of these alloys on the thermal barrier coating (TBC) cyclic life was examined. TBC life was examined by cycling substrates coated with the different bond coats and a ZrO 2-7wt.%Y 2O 3 TBC in an air-rich burner rig flame between 1150 °C and room temperature. The oxidation kinetics of the three bond coat alloys were examined by isothermal oxidation of monolithic NiCrAlY coupons at 1083 °C. The Ni-35Cr-6Al-0.95Y alloy exhibited comparatively high isothermal oxidation weight gains and provided the longest TBC life, whereas the Ni-16Cr-6Al-0.3Y alloy had the lowest weight gains and provided the lowest TBC life. The results clearly show that, although bond coat oxidation is known to have a strong detrimental effect on TBC life, it is not the only bond coat factor that determines TBC life. The α-Cr phase was observed in the bond coat metal for the Ni-35Cr-6Al-0.95Y and Ni-18Cr-12Al-0.3Y alloys, but not for the Ni-16Cr-6Al-0.3Y alloy. The presence of α-Cr may reduce the coefficient of thermal expansion of the Ni-35Cr-6Al-0.95Y and Ni-18Cr-12Al-0.3Y alloys, thereby increasing the TBC lives on these bond coats relative to the Ni-16Cr-6Al-0.3Y coating.