Glass Transition Behavior of Fe–Al–B–Si Amorphous Alloys

Abstract

Amorphous Fe–Al–B–Si alloys have been found to exhibit a glass transition phenomenon before crystallization. The composition range in which the glass transition is observed extends from 3 to 20%Al and 25 to 28%(B+Si) for Fe_{100−x−2.8y}Al_xB_ySi_1.8y, and 12 to 23%B and 7 to 16%Si for Fe_93−x−yAl₇B_xSi_y. The glass transition temperature (T_g) increases from 793 to 836 K with increasing B and Si contents and there is no distinct change in T_g with Al content. The largest values of the temperature span ΔT_x (=T_x−T_g) between crystallization temperature (T_x) and T_g and the change in specific heat by the glass transition (ΔC_p,s→l) are 36 K for Fe₆₅Al₁₀B₁₆Si₉ and 12.8 J/mol·K for Fe₆₅Al₇B₁₈Si₁₀. The appearance of T_g for the Al-containing alloys implies an increase of the stability of the supercooled liquid against the precipitation of crystalline phases. The increase of the thermal stability is inferred to originate from the development of a more homogeneously mixed disordered structure through an optimization of the atomic size ratio resulting from the existence of Al with the largest atomic size.