A DETAILED STUDY TOWARD THE NANO -CRYSTALLIZATION OF α – Fe IN Fe55-XCr18Mo7B16C4 BULK AMORPHOUS ALLOY

Crystallization of ? – Fe phase during annealing process of Fe55Cr18Mo7B16C4 bulk amorphous alloy has been evaluated by X- ray diffraction, differential scanning calorimetric tests and TEM observations in this research. In effect, crystallization mechanism and activation energy of crystallization were evaluated using DSC tests in four different heating rates (10, 20, 30, 40 K/min). A two -step crystallization process was observed in the alloy in which ?–Fe phases was crystallized in the first step after annealing process. Activation energy for the first step of crystallization process (i.e. ? – Fe phase) was measured to be 276 (Kj/mole) according to Kissinger kinetic model. Furthermore, Avrami exponent calculated from DSC curves was two and a three -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. It is also known from the TEM observations that crystalline ? – Fe phase nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology.