The oxidation kinetics of SmCo alloys

SmCo alloys form the basis of excellent permanent magnets with potential service applications up to 550 °C. It is suspected, however, that their oxidation behaviour may limit their usefulness but this is a relatively unstudied subject. In this present work, two grades of Sm2(Co,Fe,Cu,Zr)17-based alloys were oxidised in air at temperatures between 300 and 600 °C, and the kinetics of the internal oxidation zone (IOZ) measured using SEM examination. The IOZ was found to grow parabolically with time, with an activation energy of ∼143 kJ mol−1 for growth in both the directions perpendicular and parallel to the c-axis alignment. The extent of penetration of the IOZ was always greater in the perpendicular than in the parallel directions, however.