Purifying Fe-based amorphous alloys to enhance glass-forming ability by designing a novel refining slag

Abstract

• A novel refining slag design strategy was proposed for Fe-based amorphous alloys. • The designed SiO 2 -CaO-Al 2 O 3 -B 2 O 3 refining slag was effective in enhancing the GFA. • Inclusions with small lattice disregistry can promote the heterogeneous nucleation. • The enhanced GFA is due to the reduced impurities and inclusions after refining. Designing low melting point and low basicity refining slag suitable for Fe-based amorphous alloys and understanding the inclusions’ formation, removal, influencing mechanisms are quite vital in the fields of metallurgy and materials. In this study, a novel 13%SiO 2 -32%CaO-30%Al 2 O 3 -25%B 2 O 3 (wt.%) refining slag was designed after careful calculations of the liquid phase region, slag-metal equilibrium, surface tension, viscosity, deoxidation capability and sulfur distribution ratio. After refining with our designed slag, the content of impurities and the number density of inclusions in a representative Fe 83 Si 2 B 15 (at.%) amorphous alloy were significantly reduced. Moreover, the glass-forming ability (GFA) of the alloy was also enhanced, enabling the preparation of amorphous ribbons with a lower cooling rate. Based on the impurities in Fe-based amorphous alloys as well as the calculated oxide and sulfide free energy diagrams, CaO, SiO 2 , Al 2 O 3 oxides and CaS, TiS, MnS sulfides will form in the master alloy. The high melting point inclusions in the melt are generally removed via a floatation-separation-absorption process and the Mn, Ti, S impurities are removed via slag-metal interface reactions during refining. As for the detrimental effect of inclusions on glass formation, the small lattice disregistry between Ti, Mn-containing inclusions and primary α-Fe gains reveal that these inclusions are effective in promoting the heterogeneous nucleation, and therefore greatly deteriorate the GFA. These findings are important and provide an ideal solution to purifying the Fe-based amorphous alloys by refining and enhancing the GFA for industrial production.