Investigation of microstructural changes of Pt-Al-7% YSZ coating during high-temperature hot corrosion and its effect on tensile properties of coated Rene-80 superalloy at 950 °C

Abstract

In the present study, the microstructural changes in Pt-Al-7%YSZ coating on Rene-80 superalloy after 10, 20, and 40 cycles of hot corrosion and the effect of hot corroded coating on the tensile properties of Rene-80 substrate at 950 °C were investigated. For this purpose, the cross-section and fracture surface of the coating, substrate, and coating/substrate interface, were studied and the correlation between tensile behavior and microstructural changes of substrate and coating was evaluated. It was found that the effect of coating's microstructural changes on the tensile properties is less than the effect of microstructural changes on the substrate. As the cycles of hot corrosion increased, yield strength and tensile strength changed. This event was attributed to the γ' precipitates and volume fraction and the average size of voids in the substrate. The intergranular cracks were nucleated in the substrate from micro-voids in the adjacent areas to MC carbides, grew, and coalesced. However, the most influential factors in the coating on the tensile properties of coated samples were thermally grown oxide (TGO) stresses and thermal stresses due to the difference in thermal expansion coefficients between the coating layers and substrate and increasing the release rates of these stresses. The strain energy release rate (GC) was highest in TGO/Pt-Al, and coating degradation occurred through nucleation of delamination and longitudinal cracks in the TGO/Pt-Al interface and propagation of some of these cracks to the substrate.