Investigation on High Temperature Water Vapor Corrosion Behavior of MCrAlY/8YSZ Thermal Barrier Coatings
The high-temperature water vapor corrosion behavior of MCrAlY/8YSZ thermal barrier coatings (TBCs) was investigated to address the premature failure of bond coats in hydrogen-blended gas turbine environments. Four MCrAlY bond coats with distinct compositions and microstructures were deposited on MM247 substrates via high-velocity oxy-fuel (HVOF) spraying and atmospheric plasma spraying (APS), followed by APS-deposited 8YSZ ceramic top coats. Corrosion tests were conducted at 1050 °C for 100 h under water vapor contents of 0 vol.%, 45 vol.%, and 80 vol.%. Scanning electron microscopy and energy-dispersive spectroscopy revealed a dual-layer oxide scale consisting of spinel oxides and Al2O3 on all samples. The Al2O3 layer exhibited a continuous, dense microstructure, whereas the spinel oxide grew unevenly with internal porosity. Increasing water vapor content from 0% to 45% and then to 80% progressively elevated the spinel oxide fraction, accelerating bond coat degradation. HVOF-sprayed bond coats, characterized by dense lamellar interfaces, effectively suppressed inward penetration of corrosive species and outward diffusion of metal ions, yielding significantly lower spinel content than APS-sprayed counterparts. The addition of Ta promoted rapid formation of a stable Al2O3 scale and inhibited outward diffusion of other metal cations, with the NiCoCrAlTaY bond coat producing the lowest spinel oxide content and superior protection. These findings indicate that dense bond coat microstructures and Ta alloying are critical for extending TBC service life in high-humidity or hydrogen-blended combustion environments.