Nanocrystalline Fe(Co)ZrMoBCu soft magnetic alloys: A transmission electron microscopy study of the microstructures

Abstract

Nanocrystalline Fe81Zr7Mo2B9Cu1 and Fe40.5Co40.5Zr7Mo2B9Cu1 alloy ribbons were prepared by annealing the as-quenched amorphous alloys at their first exothermic peak temperature. The primary crystallization phases of Fe81Zr7Mo2B9Cu1 and Fe40.5Co40.5Zr7Mo2B9Cu1 consisted of nanoscale body-centered cubic α-Fe and α-FeCo grains, respectively. The microstructures and compositions were analyzed via transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM), and area maps were obtained through energy-dispersive spectroscopy (EDS). The addition of Co decreased the mean grain size (D) and broadened the grain-size distribution (σ). The effect of the addition of Co on the Cu clusters and element distribution was studied in detail. Scanning transmission electron spectroscopy combined with energy-dispersive spectroscopy revealed that both alloys contained Cu clusters; the Fe40.5Co40.5Zr7Mo2B9Cu1 alloy exhibited a Cu-cluster density similar to that of the Fe81Zr7Mo2B9Cu1 alloy. Both alloys contained relatively less Fe in their residual amorphous phases than in their nanocrystals, with the nanocrystals in Fe40.5Co40.5Zr7Mo2B9Cu1 containing less Co than in the residual amorphous phase. Fe40.5Co40.5Zr7Mo2B9Cu1 exhibited higher specific saturation magnetization (Ms), specific remanent magnetization (Mr) and larger coercivity (Hc) than Fe81Zr7Mo2B9Cu1.