Crystallisation kinetics of Fe₄₀Ni₄₀B₂₀ amorphous alloy

The crystallisation of amorphous Fe₄₀Ni₄₀B ₂₀ 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.