Crystallisation kinetics of Fe40Ni40B20 amorphous alloy

The crystallisation of amorphous Fe40Ni40B20 alloy upon isothermal annealing was investigated using power-compensating differential scanning calorimetry supported by X-ray diffraction and transmission electron microscopy for microstructure analysis. It was found that the crystallisation occurs in one step mainly by coupled growth of lamellar fcc (Fe,Ni) and orthorhombic (Fe,Ni)3B phase. Kinetic analysis of the crystallisation reaction was performed by fitting a modular model of phase transformation simultaneously to several isothermal transformation curves. It was thus found by fitting to transformation-rate data obtained without a pre-annealing treatment that above the glass transition temperature, the crystallisation reaction proceeds by continuous nucleation of new crystalline particles and by growth with a growth law slower than linear growth in 3D, attributed to the lamellar microstructure. By introducing additional experimental data, for variable nucleation mode realised by pre-annealing, separate activation energies for nucleation and for growth could be determined involving fitting to, simultaneously, the set of all transformation rate data comprising both data obtained without pre-annealing and data obtained after pre-annealing.