Characterization and properties of soft-magnetic (Fe0.5Co0.5)75B21Nb4 metallic glass treated with cryogenic treatment and relaxation annealing

The effect of cryogenic treatment (CT) and relaxation annealing treatment (AT) on the local atomic arrangement (dm), thermodynamic stability, soft-magnetic properties, microhardness (Hv), and corrosion resistance of as-spun (Fe0.5Co0.5)75B21Nb4 metallic glasses (MGs) have been studied. On the premise of maintaining a full amorphous phase, appropriate CT and AT are conducive to achieving synergy of the increased saturation magnetization (Ms) and reduced coercivity (Hc). Shallow CT at 213 K displays a significant optimization enhancement effect on the soft-magnetic properties of MG. Based on the low activation energy of nucleation and the increased activation energy of growth, appropriate CT is beneficial for achieving uniform annealed nanocrystals for the amorphous phase. On the basis of the correlation between free volumes and potential energy, it suggests that the Hc variation depends on the expansion and contraction behavior of amorphous phases after different CTs. The fitting formulas of Hc ~ dm and Ms ~ Hv correlations demonstrate a more solid linear relationship between soft-magnetic parameters and the contents of free volume and degree of dense random packing. Moreover, the pitting resistance is improved by appropriate CT and AT, which is characterized by promoting Nb-rich passive film stability formed during electrochemical corrosion in 3.5 wt.% NaCl solution.