Oxidation behavior of plasma sprayed Al@NiCr with cyclic thermal treatment at different temperatures

Freestanding and inhomogeneous coating was prepared by atmospheric plasma spray using Al@NiCr powder. Oxidation kinetics and mechanism are discussed after cyclic oxidation in air. Slight interdiffusion occurred at 800 °C but oxidation process took a dominant position at higher temperature. The oxidation of Cr turned significant above 1100 °C and volatilized as CrO3. The oxidation of Ni also became severe at 1100 °C. The oxidation was suppressed when internal channels were filled up with oxides. Then two stages for oxidation appeared, both of which obeyed parabolic rate law. The slow oxidation of external surface played a key role at the second stage.

► Freestanding and inhomogeneous coating was prepared using Al@NiCr powder.
► Unalloyed aluminum in as-deposited coating caused a low electric potential.
► Oxidation of Cr and Ni turned significant at 1100 °C since CrO3 volatilized.
► Suppression of internal oxidation resulted in two parabolic stages of kinetic curves.