The microstructures and magnetic properties of some cast and annealed Pr-Fe-Cu-B alloys (abstract)

Abstract

This paper reports the results of investigations of the microstructures and magnetic properties of some cast and annealed Pr-Fe-Cu-B alloys represented by the formulas PrxFe94.3−xCu2.0B3.7, Pr20.5Fe75.8−xCuxB3.7, and Pr20.5Fe77.5−xCu2.0Bx. Microstructural examination of these alloys showed that most of them exhibited Pr2Fe14B plate-like grains with the c axis perpendicular to the plate surface and there was c-axis alignment in the plane perpendicular to the predominant cooling direction. SEM examination of the alloys showed that the copper was concentrated in the intercrystalline regions and only trace quantitiies (<0.4 at. %) of copper were detected in the Pr2Fe14B phase. A eutectic mixture and a needle-like phase were observed in the intercrystalline regions. The permanent magnetic properties of the alloys, subject to various casting conditions and heat treatments, were investigated and enhanced properties were observed perpendicular to the predominant cooling direction. The largest (BH)max value (70 kJ m−3) was achieved for the Pr20.5Fe73.8Cu2.0B3.7 alloy after annealing at 1000 °C for 5 h to remove the free iron. An improvement in the intrinsic coercivity of 73% was observed for this alloy on annealing for 3 h at 500 °C. Attempts have been made to correlate the permanent magnetic properties of the alloys with their corresponding microstructures.