Oxidation behaviour and scale morphology of normal-grained CoCrAl alloy and its sputtered microcrystalline coating

Abstract The oxidation behaviour and scale morphology of normal-grained Co-30Cr-5Al alloy and its sputtered microcrystalline coating were studied at 1100 °C in air. The normal-grained alloy exhibited typical breakaway oxidation. Up to 25 h exposure the normal-grained alloy showed protective behaviour due to the formation of α-Al 2 O 3 scale, while after 25 h oxidation the weight increased rapidly due to the cracking and spalling of the Al 2 O 3 scale and the formation of Cr 2 O 3 . The sputtered microcrystalline coating exhibited excellent protection compared to the normal-grained alloy. Neither breakaway, scale cracking nor scale spalling was found.