The Cyclic Hot Corrosion Behavior of Pt–Al–7%YSZ Coating

Abstract

In this study, the microstructure and cyclic oxidation of Pt–Al–7%YSZ thermal barrier coating applied on Rene-80 superalloy were investigated after Type I hot corrosion. The field emission scanning electron microscope and X-ray diffraction were used to evaluate the microstructure and phase identification, respectively. Na2SO4 was added to the surface of the coating for hot corrosion tests. The tests were carried out by the repeated cycles of heating at 900 °C for 30 and 60 min and rapid cooling to 400 °C in 10 min. Before the cyclic hot corrosion test, the specimens were coated with the platinum electroplating, high-activity low-temperature aluminizing, and the thermal spray of 7% yttria-stabilized zirconia (YSZ), respectively. The results showed that the cyclic hot corrosion mechanisms were the basic fluxing of primary thermally grown oxide (TGO), the formation of chromia, spinel and nickel oxides (C.S.N oxides) and Ni–Cr perovskites on the oxide scale. The type I cyclic hot corrosion resistance of Pt–Al–7%YSZ coating decreased with the number of thermal cycles due to a decrease in Al, an increase in Cr concentration, and increase in the volume fraction of C.S.N oxides and Ni–Cr perovskites in the oxide scale. As the number of thermal cycles increased, the oxide scale growth stresses and thermal mismatch stresses increased, leading to TBC degradation by the rumpling and ratcheting mechanisms in the Pt–Al/TGO interface. However, in lower thermal cycles, internal hot corrosion, and the formation of Kirkendall pores at the substrate/Pt–Al interface caused TBC degradation.