Role of P on amorphization, microstructure, thermo-physical and soft magnetic properties of Fe-rich FeB(P)SiNbCu melt-spun alloys

The influence of P on amorphizing ability, as-quenched microstructure, thermo-physical and soft magnetic properties of Fe-rich (i) Fe81B15-xPxSi2Nb1Cu1 (ii) Fe82B14-xPxSi2Nb1Cu1 and (iii) Fe83B13-xPxSi2Nb1Cu1 (x = 0, 2, 4, 6, 8 at%) melt-spun alloys are investigated. The substitution of P improves amorphization of alloys and restricts the formation of hetero-amorphous microstructure for Fe 83 at% ribbons at around (x = 8). The improvement in short range ordering of P containing clusters with varying Fe content has been discussed within the framework of Cluster-Glue atom model and supported by experimental thermal parameters. The optimal P content in Fe-rich alloys in the range of 4 <= x <= 6 delivered favourable thermal properties of high primary and secondary crystallization onset temperature viz; T-x1, T-x2 and temperature span Delta T between these onsets. The P substitution drastically restricts the precipitation of secondary crystallites with reduced enthalpy of secondary crystallisation (Delta H-2) during annealing and favourably assists in attaining maximum magnetic moment during the primary crystallization stage. Moreover, the P substitution (4-8 at%) effects refinement of alpha-Fe nanocrystallites and promotes low coercivity (H-c < 20 A/m) in nanocomposite alloys. On contrary, the P substitution linearly reduces saturation magnetization (M-s) by weakening ferromagnetic exchange coupling and ferromagnetic dilution. An optimal content of 4 at% P offers favourable combination of low H-c and High M-s in both amorphous and nanocomposite state.