NANOCRYSTALLIZATION MECHANISMS OF Fe۵۲Cr۱۸Mo۷B۱۶C۴Nb۳ BULK AMORPHOUS STEEL

Crystallization kinetics of Fe۵۲Cr۱۸Mo۷B۱۶C۴Nb۳ alloy was evaluated using X-ray diffraction, differential scanning calorimetric (DSC) tests and TEM observations in this research work. In effect, crystallization and growth mechanisms were investigated using DSC tests in four different heating rates (۱۰, ۲۰, ۳۰, ۴۰ K/min) and kinetic models (i.e. Kissinger- Starink, Ozawa, and Matusita methods). Results showed that a two -step crystallization process occurred in the alloy in which α - Fe and Fe۳B phases were crystallized respectively in the structure after heat treatment. Activation energy for the first step of crystallization i.e., α - Fe was measured to be ۴۲۱ (kj/mol) and ۴۴۲ (kj/mol) according to both Kissinger- Starink and Ozawa models respectively. Further, Avrami exponent calculated from DSC curves was ۱.۶ and a two -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. TEM observations reveal that crystalline α – Fe phase nucleated in the structure of the alloy in an average size of ۱۰ nm and completely mottled morphology