Role of Ta and Nb alloying elements on the viscosity of Fe-B-Si melts

Abstract

Alloying of Fe – B – Si alloys is a key issue in the preparation of promising bulk amorphous materials. In the present study, we examine temperature and concentration dependences of the kinematic viscosity of (Fe0.75B0.15Si0.10)100-xMx (M = Ta, Nb, x = 0–4) melts. Detailed structural analysis is performed. The results demonstrate importance of sedimentation processes for understanding temperature dependences of the viscosity with a concentration of alloying elements of more than 1 at.% Ta and 1.5 at.% Nb. The sedimentation processes are associated with the presence of the refractory compounds, FeTaB and NbB2, in the (Fe0.75B0.15Si0.10)100-xTax and (Fe0.75B0.15Si0.10)100-xNbx (x = 0–4) alloys, respectively. Alloying elements, Ta and Nb, even at low concentrations, have different effect on the viscosity of Fe–B–Si melts. Small Ta additions slightly affect the viscosity, while the Nb additions increase its value. The concentration dependences show the local maxima of viscosity at 1 at.% Ta and 3 at.% Nb. Ab initio calculations show the difference in the chemical interaction of Ta and Nb atoms in the melts. The alloying preserves the main features of the melt local structure and increases the dispersion of component interaction radii which improves the amorphization ability.