MICROSTRUCTURAL AND MAGNETIC STUDIES ON PR-FE-B-CU ALLOYS

A detailed study on the microstructure and magnetic properties of alloys Pr20.5Fe74.0B3.5Cu2.0(A) and Pr17.0Fe76.5B5.0Cu1.5(B) has been carried out as a precursor to a study of the effects of high-temperature mechanical deformation on these materials. In the cast condition, the microstructure of alloy A consisted of three phases in the cast condition: Pr2Fe14B matrix phase, Pr-rich grain-boundary phase, and free Fe inside the matrix phase. The microstructure of alloy B in the cast state consisted of four phases: the same three phases as those observed in alloy A together with the PrFe4B4 phase. On annealing alloy A, an extra phase with needlelike or irregular form was observed in the grain-boundary regions. EDX (energy dispersive x-ray spectrometer)/WDX (wavelength dispersive x-ray spectrometer) analysis indicated that this phase is the Pr (Fe0.94Cu0.06)2 phase. In alloy B, the microstructures were not altered radically by annealing at high temperature except for the disappearance of the free iron. Alloy A exhibited much better permanent magnetic properties than those of alloy B, and this was attributed to grain size and improved magnetic isolation of the individual grains. The effects of low-temperature annealing on the magnetic properties at 500-degrees-C have also been investigated.