MAGNETIC-PROPERTIES OF PR-FE-B ALLOY POWDERS PREPARED BY MECHANICAL GRINDING

The effect of ball milling on the magnetic properties of the Pr15Fe80B5 alloy, whose as-cast structure was composed of matrix phase Pr2Fe14B and Pr-rich and alpha-Fe phases, has been investigated by measuring (i)H(c), thermomagnetic curves, and x-ray diffraction (XRD) patterns. By ball milling using a planetary ball mill up to 96 h, (i)H(c) decreased with the amorphization of the matrix and Pr-rich phases. However, subsequent heat treatments gave rise to the marked increase of (i)H(c). The alloy, after 48 h of ball milling and subsequent 600-degrees-C annealing possessed (i)H(c) of 17.4 kOe, B(r) of 5.8 kG, and (BH)max of 6.5 MGOe. This alloy showed sharp diffraction peaks of Pr2Fe14B phase, while the alpha-Fe phase peak, which persisted through the ball milling process, almost disappeared. The high (i)H(c) of the Pr-Fe-B alloy, subjected to optimum milling and subsequent annealing, was attributed to a very fine Pr2Fe14B phase precipitation from the amorphous state and to the effective solution of the alpha-Fe phase into the matrix phase. Also, a small addition of Cu to the Pr15Fe80B5 alloy was found to increase the coercivity. Further, the alloy milled for 12 h and annealed at 600-degrees-C for 1 h showed (i)H(c) of 19.7 kOe, B(r) of 7.0 kG, and (BH)max of 10.2 MGOe.