Oxidation and refreshing behaviors of P-containing Fe-based amorphous ribbons

Oxidation behaviors of Fe₇₈B₁₃Si_{9 − x}P_x (x = 0, 1, 3, 5 and 7) amorphous ribbons were investigated and a refreshing method by annealing in reductive atmosphere were successfully developed by considering the changes of magnetic properties and P content. It is found that the amorphous ribbons with high P content are prone to be oxidized at the beginning of a traditional annealing process. When the annealing process was under reductive atmosphere, however, not only the oxidation can be avoided but also the oxidized ribbon can be refreshed. It is found that, although the color is changed, the amorphous structure for both the oxidized and refreshed ribbons is not changed with the annealing conditions. The refreshing can recover the excellent soft magnetic properties of the alloys with P content lower than 5 at.%. The magnetization process characterized by magnetic domains has revealed the effect of refreshing ability to the oxidized ribbon. It is further confirmed that the refreshing mechanism of the oxidized layer is the valence state change of iron ions from high to low through the seriously oxidized Fe₇₈Si₂B₁₃P₇ amorphous ribbon.