Effect of surface modification on mechanical properties and thermal stability of Sm-Co high temperature magnetic materials

The effects of different surface modifications on the mechanical properties and thermal stability of Sm-Co high temperature magnets are reported in this paper. The fracture toughness was increased by 76% for the specimens modified with the Ni plating from sulfamate electrolyte. Compared to the uncoated magnets, the thermal stability of the modified magnets was improved by 143% in high vacuum condition for aging at 500 degrees C up to 3000 h and by 761% in air for aging at 500 degrees C up to 2700 h. Microstructures of the specimens with and without surface modifications were studied using scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS), showing different fracture patterns. The improvements in mechanical properties were made by closing the infinite crack-origin sites on the surface of the magnets with ductile metal. The striking improvement in thermal stability was achieved by sealing the magnet body with corrosion resistive metal to limit oxidation. The adhesive bond strength between the magnet and the modified surface plays an important role in these improvements. The nickel plating from sulfamate electrolyte provides epitaxial growth of Ni from the surface of the Sm-Co magnet, which results in a stronger bond strength in between the Ni and the base material than that of the Sm-Co base material itself. Improved mechanical properties and thermal stability will benefit the development of compact, high power density electric propulsion devices for NASA's space missions. (c) 2006 Elsevier B.V. All rights reserved.