Evolution and Removal of Inclusions in Fe-Based Amorphous Alloys

Fe-based amorphous alloys generally suffer from deteriorated glass forming ability and soft magnetic properties due to the impurities in industrial raw materials. In this study, the inheritance of impurities from raw materials and evolution of inclusions were systemically investigated in a series of FeB, FeBSi, FeBSiP and FeBSiPNb alloys with an increasing compositional complexity. The Mn, Al, Ti, S, C and Ca impurities in the raw materials were found to form MgO-Al2O3 or composite inclusions with MgO-Al2O3 cores and shells of sulfides, nitrides and carbides in the master alloys, where Mg originated from the MgO crucible or the MgO-B2O3 refining slag. By comparison, the inclusions in as-quenched ribbons were considerably much simpler and smaller, because the high-melting-point MgO-Al2O3 and MgO-Al2O3-SiO2 inclusions are insufficient to grow up and low-melting-point sulfide, carbide and nitride inclusions will not precipitate during the rapid solidification. During refining, these high-melting-point inclusions were generally removed via a flotation-absorption process, and the Mn, Ti, S impurities in the melt diffused to the refining slag and were removed via steel-slag interface reactions. These findings are of paramount importance for developing suitable refining process to alleviate the detrimental effects of impurities in Fe-based amorphous alloys and facilitate the industrial production of high-performance soft magnetic materials.