Effects of Cr addition on structure, magnetic properties and corrosion resistance of a Fe85.5B13Cu1.5 nanocrystalline alloy

The melt-spun structure of a Fe85.5B13Cu1.5 alloy was regulated by the addition of corrosion-resistant Cr with a moderate enhancement in amorphous-forming ability, which further refines the nanostructure and improves the soft magnetic properties and corrosion resistance of corresponding nanocrystalline alloys. The results show that high-number-density α-Fe grains in size of below 10 nm are formed in the amorphous matrix of melt-spun Fe85.5-xB13Cu1.5Crx (x = 0–6) alloy ribbons, and the grain size and number density gradually decrease with the increase in Cr content. After annealing, the α-Fe average grain size (Dα-Fe) and coercivity (Hc) of corresponding nanocrystalline alloys reduce significantly with increasing x from 0 to 3, and the reduction becomes less pronounced within x = 3–6, while the saturation magnetic flux densities (Bs) steadily decreases as x increases from 0 to 6. A Fe82.5B13Cu1.5Cr3 nanocrystalline alloy with the Dα-Fe of 14.9 nm possesses excellent comprehensive soft magnetic properties with the Hc and Bs of 13.8 A/m and 1.74 T, respectively. The fine nanostructure and good magnetic softness results from the optimum combination of pre-existing α-Fe competitive growth and Cr-inhibited atom diffusion. The nanocrystalline alloys show improved corrosion resistance in NaCl solution compared to their respective melt-spun precursors, and the addition of Cr further enhances the corrosion resistance. The alloyed Cr also reduces the annealing embrittlement of the nanocrystalline alloys.