POWDER METALLURGICAL PROCESSING OF TB0.27DY0.73FE2-X(0-LESS-THAN-X-LESS-THAN-OR-EQUAL-TO-0.5) BY HYDROGEN DECREPITATION

This paper reports on the characterization of giant magnetostrictive alloys, of the general formula Tb0.27Dy0.73Fe2-x (0 < x less-than-or-equal-to 0.5), at various stages during their powder processing by hydrogen decrepitation, in order to try to optimize the process. Mass spectrometer degassing studies on hydrogenated material have shown that disproportionated material exhibits two desorption peaks and is not degassed completely with respect to hydrogen until above 600-degrees-C. The RFe2 (R = Tb0.27Dy0.73) hydride powder appears to degas at a lower temperature; however, it is thought that a high-temperature desorption peak is not present due to oxidation. Metallographic studies have shown that there is much less rare-earth-rich grain-boundary phases in sintered compacts of initial composition RFe1.5 than in cast RFe1.5 and also reveal the microstructure of hydrogenated and disproportionated RFe1.5. Wavelength dispersive x-ray analysis seems to indicate preferential loss of Dy during sintering.