Mechanism and kinetics of crystallization of amorphous Fe81B13Si4C2 alloy

Abstract

Crystallization process of amorphous Fe81B13Si4C2 alloy manifested as a slightly asymmetrical exothermic peak in temperature range 770–820K of differential scanning calorimetry (DSC) curves. Complex crystallization DSC peak was deconvoluted into three steps corresponding to formation of α-Fe(Si), Fe3B and Fe2B crystalline phases. Fe2B phase is formed from the amorphous matrix, while metastable Fe3B decomposes, providing constituents for subsequent formation of Fe2B phase. Examination of mechanism and kinetics of each individual step of crystallization yielded similar values of kinetic triplets, indicating similar crystallization mechanism for all individual phases, which was subsequently discussed using the values of Avrami exponents of individual crystallization steps. Both the range of and changes in values of the local Avrami exponent suggested the appearance of impingement, which precluded full applicability of JMA equation, and mixed nucleation type with accelerating nucleation for crystallization of all phases. Position of the transformation-rate maxima of individual crystallization steps indicates that anisotropic growth is the prevailing type of impingement. Estimation of lifetime showed very high stability of the alloy against crystallization at room temperature, with exponential decline in lifetime with temperature increase.