Multi-alloying of nanomet: conception and implementation of homogeneous nanocrystallization in high-flux density soft magnetic alloys

Abstract

This study demonstrates how multi-alloying the Fe-Si–B–P–Cu (Nanomet®) can avoid the strict requirements on the annealing scheme in terms of high heating rate and narrow annealing temperature range in order to grow a homogeneous ultrafine nanocrystalline structure. The rather restricted amorphization capability sets a low limit of the maximum thickness of the amorphous precursor. These shortcomings have their origin in the existence of detrimental pre-existing nuclei in the amorphous precursors, which in turn potentially lead to a heterogeneous crystallization. Here, we have multialloyed Nanomet with CoCNi- and CoCMo- to avoid the creation of these pre-existing nuclei. This leads to improved amorphization capability and changes a potentially heterogeneous crystallization to a homogeneous nanocrystallization over a much broader temperature range than for unalloyed Nanomet. Thus, the requirements for the annealing are much relaxed. This work encompasses quenching the amorphous precursors using melt-spinning, investigating the crystallization temperatures by calorimetry, showing the depletion of pre-existing nuclei by magneto-thermo-gravimetry, conceptualizing the crystallization dynamics using isothermal calorimetry, and finally revealing the excellent soft magnetic properties over a broad annealing temperature interval (390–490 °C for the substituted alloys compared to 410–470 °C for unalloyed Nanomet). The multi-elemental substitution of Fe with CoCMo and CoCNi in Nanomet alloy nearly maintains the saturation magnetization and the coercivity. We believe the substituted alloys provide a better alternative to Nanomet with improved amorphization capability and homogeneous nanocrystallization without any special heat treatment scheme.