Internal oxidation of Sm(CobalFe0.22Cu0.08Zr0.02)7.5 alloy at 700 °C

The internal oxidation zone (IOZ) of a Sm(CobalFe0.22Cu0.08Zr0.02)7.5 alloy formed in air at 700 °C was characterized using transmission electron microscopy (TEM). It shows that the internal oxides are varied in composition and size with depth, from mainly fine FeSmO3 in shallow area to larger Sm2O3 in deeper area. The internal oxidation also causes the formation of a thin phase transformation zone between the IOZ and the alloy. The internal oxidation mechanism, together with the oxidation-induced phase transformation of the magnetic matrix phases of the alloy, is fully disclosed.

Graphical abstractThe internal oxidation of the magnet mainly formed Sm2O3 but FeSmO3 in a shallow depth, as seen in the scanning transmission electron microscopy and corresponding X-ray mappings of Fe, Sm and O.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Sm is internally oxidized into FeSmO3 in shallow internal oxidation zone. ► Larger Sm2O3 particles occur in deeper internal oxidation zone. ► The internal oxidation causes degradation of the magnetic matrix phases. ► Formation of Sm–Cu compound in a thin layer ahead of the internal oxidation zone.