The effect of milling time upon microstructures of Pr-Fe-B HD sintered magnets prepared by a low cost powder technique

Abstract

Pr17Fe79B4 and Pr16Fe76B8 magnets have been produced using a combination of the hydrogen decrepitation (HD) process and a powder transfer technique. Sintered magnets have been prepared using HD powders ball milled from 9 to 36 hours. The effects of the milling stage upon microstructure have been investigated. In the Pr17Fe79B4 magnets four phases have been identified: Pr2Fe14B (Φ), Pr rich, Pr2Fe17 and Laves phase (PrFe2). In the Pr16Fe76B8 magnets three phases have been identified: Pr2Fe14B (Φ), Pr rich and Pr1+εFe4B4 (η). Good magnetic properties have been achieved in the Pr16Fe76B8 magnet produced using a fine powder milled for 18 hours (Br = 1.19 T and µ0iHc = 1.44 T). For the Pr17Fe79B4 magnet a longer milling time has been necessary to improve the magnetic properties (Br = 1.14 T and µ0iHc = 1.16T). In this case remanence and coercivity were slightly lower than that obtained in former due to the low boron content in the alloy (4 at.%).