The effect of a surface Cr film on the oxidation of SmCo-based magnetic alloy at 700 °C

A 4.5 μm-thick Cr film prepared by a double glow sputtering technique was deposited on a magnetic Sm(CobalFe0.22Cu0.08Zr0.02)7.5 alloy to improve its oxidation resistance. Oxidation tests in air at 700 °C indicate that the Cr film grew a Cr2O3 scale, profoundly preventing the oxidation of the SmCo-based alloy. The coated alloy only formed a ∼2.9 μm-thick internal-oxidation-affected zone (IOAZ) for 20 h. The mechanism for the formation of this IOAZ, together with its induced alloy magnetic phase transformation, is presented.