Comparative Study of High-Temperature Oxidation Behavior of Bare and Plasma Sprayed Al2O3-40%TiO2 Coated T-91, A-1 Boiler Steel and Superfer800H Superalloy in Air

In the present investigation, a plasma spray process was used to deposit bi-layer NiCrAlY/ Al2O3-40%TiO2 coating powder on three substrates namely T-91, A-1 boiler steel, and Superfer800H superalloy. The deposited coating was found to be dense, and uniform with thickness ranges from 200 to 250 µm. The oxidation behavior of both (bare and coated) specimens at elevated temperatures was ascertained by using a high-temperature furnace. The experiments were conducted over 50 cycles. In each cycle, the specimens were subjected to an isothermal temperature of 900 °C for 1 h followed by cooling for 20 min at room temperature in atmospheric air. The thermogravimetric study for both (bare and coated) specimens was conducted to find the corrosion rate by calculating the parabolic rate constant of the corroded specimens. The characterizations of the coatings before and after the high- temperature oxidation tests were investigated by employing various characterizations techniques. The result showed that the Al2O3-40%TiO2 ceramic coating significantly reduced the weight gain compared with the bare substrates. The high resistance of the deposited coating against the harsh oxidizing environment was because of the occurrence of protective phase (Al2O3, TiO2, and Al2Ti7O15) in the oxide scale.