Microstructural stability of zirconia–alumina composite coatings during hot corrosion test at 1050 °C

In the present work hot corrosion behavior of plasma sprayed zirconia–alumina coatings on Ni-base, IN-738, super alloy substrate was studied compared with normal zirconia. Hot corrosion resistance of the coatings was measured at 1050 °C using an atmospheric electrical furnace and a fused mixture of vanadium pentoxide and sodium sulfate salt.The hot corrosion test duration was 4 h in each cycle, while the specimens were cooled in the furnace. The general and peripheral conditions of the specimens were inspected. If there were any cracks or spallation in coating wedge the test was stopped, the time was recorded and coating microstructure was studied. Composite coatings of zirconia–alumina having alumina as a top coat or a mixed zirconia–alumina layer, showed better resistance in hot corrosion tests. It was concluded that alumina overlay on zirconia has promoted the hot corrosion resistance of the coatings.