Synthesis, microstructure, and hard magnetic properties of melt-spun Nd3Fe27.5Ti1.5 and its nitride

Abstract

Nd 3 Fe 27.5 Ti 1.5 alloy and its nitride were synthesized using melt-spinning, annealing, and nitriding route, and the effects of processing conditions on phase formation, microstructure, and magnetic properties were investigated. The following has been found: (1) Melt-spun Nd3Fe27.5Ti1.5 samples consist primarily of the 3:29 phase at low wheel speeds (5–10m∕s). The 1:7 phase was developed at higher wheel speed (20–25m∕s). Meanwhile, grain size is significantly reduced with increasing the wheel speed (from 33.5nm at 5m∕s down to 13.1nm at 25m∕s). As the wheel speed was increased to 40m∕s and above, the 1:7 phase disappears and an amorphous phase became dominant. (2) Annealing of the overquenched melt-spun samples transformed the amorphous phase into the 1:7 phase (when annealed at 600–700°C) or the 3:29 phase (when annealed at 800–900°C), and significant grain growth was observed when annealing temperature was at 800°C or above. (3) Nitriding at lower temperature (300–350°C) for longer time (24–45h) was preferred for introducing nitrogen atoms into the 1:7 or the 3:29 interstitial sites without destroying their crystalline structure. (4) The best magnetic properties obtained were Br=718mT, Hci=111kA∕m, and (BH)max=23kJ∕m3. This particular sample had the 1:7 phase with a grain size of ∼12nm and a nitrogen absorption of ∼4wt%.