Phases and magnetic properties of mechanically milled Pr-Fe-B-X alloys during heat treatment

Abstract

Microcrystalline Pr-Fe-B powders with high coercivity have been prepared by mechanically milling the as-cast ingot and a subsequent heat treatment. The mechanism responsible for the high coercivity is discussed with the results obtained using an X-ray diffractometer, vibrating sample magnetometer, a DC fluxmeter, a different thermal analyzer, and a transmission electron microscope. The mechanical milling process causes the refinement of Pr/sub 2/Fe/sub 14/B, alpha -Fe, and Pr-rich phases through a process of continuous fracture and cold welding. During heat treatment a new metastable phase and a layered Pr/sub 2/Fe/sub 14/B phase are formed at about 420 degrees C and 480 degrees C, respectively. The thickness of the multilayer is about 0.1 mu m. This structure provides the milled powder with the high coercivity of 13-18 kOe after the heat treatment. The addition of Ge to Pr-Fe-B alloy improves the squareness and maximum magnetic energy product of the mechanically milled alloys. >