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 a x-ray diffractometer, vibrating sample magnetometer, dc fluxmeter, differential thermal analyzer and transmission electron microscope. The mechanical milling process causes the refinement of Pr2Fe14B, 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 Pr2Fe14B 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 high coercive force of the milled powders after heat treatment.