Abstract
Crystallization kinetics of Fe 55−x Cr 18 Mo 7 B 16 C 4 Nb x (x= 0, 3) bulk amorphous alloys were analyzed using X-ray diffraction and differential scanning calorimetric (DSC) tests. In practice, crystallization and growth mechanism were evaluated using DSC tests at four different heating rates (10, 20, 30, and 40 K/min) and kinetic models. Two-step crystallization behavior was observed when Fe 55 Cr 18 Mo 7 B 16 C 4 and Fe 52 Cr 18 Mo 7 B 16 C 4 Nb 3 bulk amorphous alloys were annealed, where Fe 36 Cr 12 Mo 10 phase was crystallized in the first step of crystal-lization. Results show that Fe 36 Cr 12 Mo 10 and Fe 3 C phases were crystallized in the structures of the alloys after further annealing process. Activation energy for the crystallization of Fe 36 Cr 12 Mo 10 phase was measured to be 543 kJ/mol in Fe 52 Cr 18 Mo 7 B 16 C 4 Nb 3 alloy and 375 kJ/mol for Fe 55 Cr 18 Mo 7 B 16 C 4 alloy according to Kissinger-Starink model. Moreover, a two-dimensional diffusion controlled growth mechanism with decreasing nucleation rate was found in Fe 52 Cr 18 Mo 7 B 16 C 4 Nb 3 alloy whereas a three-dimensional diffusion controlled growth mechanism with decreasing nucleation rate was found in crystallization of Fe 36 Cr 12 Mo 10 phase during annealing of Fe 55 Cr 18 Mo 7 B 16 C 4 alloy. TEM (transmission electron microscopy) observations reveal that crystalline Fe 36 Cr 12 Mo 10 phase nucleated in the structures of the alloys in an average size of 10 nm with completely mottled morphology.