Kinetics and thermodynamics of thermally induced structural transformations of amorphous Fe75Ni2Si8B13C2 alloy

Thermally induced structural transformations of amorphous Fe75Ni2Si8B13C2 alloy have been characterized in terms of both thermodynamic and kinetic parameters of individual processes. The crystallization of the alloy occurs in temperature region around 500 °C with primary crystallization of stable α-Fe(Si) and Fe2B and metastable Fe3B phase, followed by transformation of Fe3B to Fe2B. The latter process exhibits the lowest values of apparent activation energy and change in Gibbs free energy of activated complex, as well as negative value of change in entropy of activated complex, indicating that this corresponds to transformation of one crystalline phase to another, making it the least complex of the four processes. Another set of transformations occurs around 700 °C, where two consecutive processes are observed: phase transformation of α-Fe(Si) to α1-Fe(Si) and subsequent transformation of a portion of α1-Fe(Si) to Fe2B. The consecutive nature of these processes is indicated by the fact that the first process exhibits significantly higher values of apparent activation energy and changes in Gibbs free energy and entropy of activated complex.

► Two experimental peaks observed in DSC of Fe75Ni2Si8B13C2 amorphous alloy.
► First peak deconvoluted into four steps and attributed to crystallization.
► Second peak deconvoluted into two steps and attributed to phase transformations.
► Thermodynamic and kinetic parameters of every individual process were determined.