Oxidation protection of Sm2Co17-based alloys

SmCo alloys form the basis of excellent permanent magnets with potential service applications up to 550 degrees C. However, the rapid growth of an internal oxidation zone limits their usefulness because the accompanying microstructural changes destroy the alloys' high-temperature magnetic properties within this zone. In this work, a high-temperature grade of a Sm-2(Co, Fe, Cu, Zr)(17)-based alloy was treated with a variety of potentially protective coating systems and then oxidised in air at temperatures of 450 and 550 degrees C to assess their performance. It was found that a diffused Pt coating and a paint-like overlay coating, containing Ti and Mg oxides, performed best at both temperatures. Sputtered SiO2 was effective at 450 degrees C but less so at 550 degrees C. Additionally, an alumina-based overlay coating was effective at 550 degrees C but less so at 450 degrees C. Specimen cracking and deformation during high-temperature exposure is also discussed. (C) 2012 Elsevier B. V. All rights reserved.