Effect of P addition on nanocrystallization and high temperature magnetic properties of low B and Nb containing FeCo nanocomposites

The P content dependencies of the nanocrystallization behaviors and high temperature magnetic properties of the Fe54.6Co29.4Si2.8(B0.8-YPY)14Nb1Cu1 (Y = 0, 0.2, and 0.3) alloys have been investigated. Alloys were prepared by melt spinning and subsequently annealed in an argon atmosphere to induce nanocrystallization. P addition increases primary crystallization temperature (Tx1), thermal stability (ΔTx), and activation energy (QJMA) for secondary crystallization in as-cast alloys. The saturation induction (Bs) of 1.68 T for as-cast P free alloy decreases continuously with the addition of P. However, the soft magnetic properties are enhanced for P added alloys. The XRD pattern reveals that grain refinement increases with increasing P contents. Alloys annealed at 430 °C confirm primary nanocrystallization of α-FeCo in the amorphous matrix, while annealing at 550 °C causes secondary crystallization of other non-magnetic phases as well. The magnetic moment of as-cast and annealed alloys, measured by vibrating sample magnetometry (VSM), has minimum values at two temperatures, labeled Tc1, Tc2, prior to secondary crystallization, corresponding to the ferromagnetic transitions of as-quenched amorphous and residual amorphous phase, respectively. The stabilization of amorphous phase delays primary crystallization, resulting in increase of Tc1 for P-rich as-cast alloys.