The outstanding effect and mechanism of non-inert casting atmospheres on glass forming ability of P-containing Fe-based soft magnetic bulk metallic glasses

Abstract

Generally, amorphous alloys are fabricated in an inert atmosphere—Ar to avoid crystallization and gain high glass forming ability (GFA). In this work, the effect of non-inert casting atmospheres (N2, air and O2) on the GFA of Fe76Si9B10P5, Fe76Si8B10P5Mo1, Fe77Mo2P10C4B4Si3 and [(Fe0.8Co0.2)0.75B0.2Si0.05]96Nb4 soft magnetic bulk metallic glasses (BMGs) was systematically investigated. Surprisingly, contrary to existing experience, while the GFA of [(Fe0.8Co0.2)0.75B0.2Si0.05]96Nb4 alloy remains the same as cast in Ar, it was found that the non-inert casting atmospheres can dramatically improve the GFA of P-containing Fe-based BMGs, especially in oxidizing casting atmosphere, with no influence in their thermal properties and magnetic properties. The results also indicated the surface composition of the P-containing Fe-based BMGs varied much with the casting atmospheres whilst the bulk composition remain unchanged. Moreover, plausible reasons were eliminated and underlying mechanism was elucidated. The decreased surface tension resulted from the segregation of P element of the P-containing Fe-based liquids during the melting process leads to the crystallization occurring in the surface layer rather than in the central area. At last, the enhancement of GFA by non-inert casting atmospheres were mainly ascribed to the increased surface tension resulting from the elimination of oxygen element for the oxidizing (air and O2) atmosphere and the alloying effect of nitrogen element for the N2 atmosphere, respectively. The new understanding about the non-inert atmosphere and metallic amorphous formation is expected to benefit the composition design of amorphous materials with better GFA and advances in the manufacture of amorphous alloys.