Effect of a thin Al2O3 film on high temperature oxidation of a Sm(Co0.68Fe0.22Cu0.08Zr0.02)7.5 alloy

• The Al2O3 film offers better protection than the Cr2O3 film in air at 500–700 °C.
• An internal-oxidation-affected zone (IOAZ) forms below Al2O3 film at 600 and 700 °C.
• IOAZ consists of a thin outer Co–Fe band and a thicker internal oxidation zone (IOZ).
• Oxidation of Sm decomposes the magnetic matrix phases in IOZ.
• No significant degradation of the magnetic matrix phases is seen below IOZ.

The oxidation of a Sm(Co0.68Fe0.22Cu0.08Zr0.02)7.5 magnetic alloy deposited with a thin Al2O3 film has been studied. The Al2O3-coated alloy exhibits almost no oxidation at 500 °C and only forms a few-micrometers-thick internal-oxidation-affected zone (IOAZ) at 600 and 700 °C for 20 h exposure to air. The effect of the Al2O3 film on the oxidation degradation of magnetic phases of the alloy is disclosed based on microstructural characterizations of the IOAZ. The result also shows that the Al2O3 film offers better protection than the Cr2O3 film reported previously.