The effect of Si addition on the microstructure and hard magnetic properties of Nd-rich Nd-Fe-B melt spun ribbons

Increasing the Nd content in melt-spun Fe-Nd-b ribbons beyond the stoichiometric concentration (11.76 at.%) and up to 20 at. %, the coercivity (sub j H sub c) progressively increases due to the presence of Nd-rich phase(s) at the Nd sub 2 Fe sub 14 B grain boundaries which is though to damp the nucleation of reverse domains. However, these alloys have relatively low remanence (J sub r) and maximum energy product (BH)sub max. because of dilution by the Nd-rich phase. In an attempt to improve Jr of a high coercivity alloys, Si was substituted for Fe in N sub 18 Fe sub 76-x B sub 6 Si sub x (x = 0-2.5 at. %). The ribbons of various thicknesses were produced for roll speeds in the range 12 to 25 m/sec. In these alloys, Si does not improve the remanence, as previously observed for low Nd-alloys, while, on the other hand, the coercivity is slightly improved. The optimum properties were found for 2 at.% Si. The coercivity increases ( about 1850 to about 1940 kA/m) for Si contents up to 2.0 at.%, while on further increasing Si content (2.5 at. %) causes a decrease in coercivity ( about 1380 kA/m). The J sub s (1.0-1.1 T) and remanence (0.68-0.72 T) were fairly constant for all compositions. The maximum energy product was found to lie in the range 70-95 kJ/m sub 3. (author)