Oxidation resistance improvement of Zr-4 alloy in 1000 °C steam environment using ZrO2/FeCrAl bilayer coating

A ZrO2/FeCrAl bilayer coating was prepared on Zr-4 alloy. Plasma electrolytic oxidation (PEO) was used to synthesize the ZrO2 buffer layer and magnetron sputtering was used to deposit the FeCrAl outer layer. The oxidation resistance of the ZrO2/FeCrAl coated Zr-4 alloy was investigated by using 1000 °C steam oxidation tests and was compared with the mono-layer FeCrAl coated and uncoted Zr-4 alloys. Morphologies, phase compositions and elemental distributions of the ZrO2/FeCrAl and FeCrAl coated Zr-4 alloys before and after the steam oxidation tests were characterized by SEM, XRD and EDX mapping and line scans. Results indicated that the introduction of the ZrO2 buffer layer effectively eliminated the high temperature inter-diffusion between FeCrAl and Zr-4 alloy, and consequently improved the adherence and integrity of the FeCrAl layer after the 1000 °C steam oxidation. As a result, the parabolic rate constant of the ZrO2/FeCrAl coated Zr-4 alloy was decreased by about 20 times compared with that of the uncoated and FeCrAl coated Zr-4 alloys in 1000 °C steam environment.