Effect of a thin Cr2O3 film on oxidation at 600 °C of a Sm(CobalFe0.22Cu0.08Zr0.02)7.5 alloy

A Sm(CobalFe0.22Cu0.08Zr0.02)7.5 magnetic alloy, after having been arc-ion-plated with a thin Cr2O3 film, was dramatically increased in oxidation resistance. It formed an internal oxidation-affected zone (IOAZ) with a thickness only about 1.5 μm at 600 °C in air for 20 h. TEM characterizations showed that the IOAZ was double-layered, consisting of an outer extremely thin Co-phase band and an inner oxidation zone with a matrix of Co-Fe solid solution dispersing Sm2O3 particles. The process for the formation of the IOAZ has been also presented in detail.