Processing - property - microstructure relations in Fe-M-Nd-C (M=Cu,Ga,Nb,Al) based ingot magnets

The effects of composition, annealing temperature and annealing time on the magnetic properties and microstructure of Fe66M2Nd20C9.5B0.5 (at %) (M = Ga,Nb,Cu,Al) ingot magnets are presented. It has been found that the magnitude of the hard magnetic properties, which evolve during the solid state transformation Fe17Nd2Cx to Fe14Nd2C, depend on the additive elements. These additions, which change the properties of the intergranular phase, affect mass transfer and the transformation process. In general, the elements which decrease the melting temperature of the intergranular phase accelerate the transformation process, and those which increase this temperature retard the transformation. Coercivities up to 880 kA/m combined with a remanence 0.58 T were produced in alloy ingots with M = Cu, annealed for 5 h at temperatures in the range 800-1000 C. The initial grain size was found to be crucial in producing good magnetic properties and coercivities as high as 980 kA/m were achieved Fe-Nd-C-B alloy magnets hot pressed from microcrystalline melt spun ribbon. A modest increase of remanence (approx 0.7 T) was achieved by die-upset forging of ingot alloys. (author). 15 refs, 9 figs, 2 tabs