MURI-96 High Temperature Advanced Magnets

A comprehensive and systematic study has been made on Sm(CO(sub bal)Fe(sub v)Cu(sub y)Zr(sub x))(sub z) magnets to completely understand the effects of composition and processing on their magnetic properties with the aim to increase their operating temperature. The homogenized Sm(Co, Fe, Cu, Zr)(sub z) magnets have a featureless microstructure. A cellular/lamellar (2:17R cells surrounded by 1:5 cell boundaries superimposed on 2:17H lamellar) microstructure develops after 2-3 hours of aging at 800-850 deg C, but the coercivity increases only after a subsequent slow cooling to 400 deg C. During the cooling, diffusion takes place and Cu is concentrated in the 1:5 cell boundaries and Fe in the 2:17R cells. Our studies have led to compositions with operating temperatures above 400 deg C and with coercivities as high as 10 kOe at 500 deg C(sup i). The high temperature performance of these magnets is very sensitive to the Cu content, which is believed to control both the coercivity and its temperature dependence. Furthermore, we developed a more economical heat treatment processing for higher Cu content magnets.