Crystallization kinetics of the Fe₄₀Ni₄₀P₁₄B₆ metallic glass in an extended range of heating rates

The effect of heating rate (in the range of 0.083–3.333 K s⁻¹) on the parameters of thermal stability and crystallization kinetics of the Fe₄₀Ni₄₀P₁₄B₆ metallic glass has been investigated by differential scanning calorimetry and X-ray diffraction. An analytical model of glass crystallization describing the homogeneous nucleation rate, the velocity of interface-limited growth, the number of crystal volume density in crystallized samples as well as the crystallization kinetics at constant rate heating is presented. A modified procedure of estimation of thermodynamic and kinetic parameters governing the rate of crystal nucleation and growth based on the use of the measured heating rate-dependent variations of the volume fraction crystallized and the average grain size is proposed. The values of the effective diffusivity have been estimated by the Kissinger-like isoconversional method accounting the contribution of both the free energy difference and the specific interfacial nucleus-melt energy changes estimated from the structural data. It has been shown for the first time that the shapes of the non-isothermal experimental kinetic crystallization curves measured at the heating rates ≤ 1.333 K s⁻¹ are well described by the approximate analytical equation and the values of the Avrami exponent lowering from 5.5 to 2.3 with the heating rates increasing have been estimated. The evaluated ranges of the nucleation rate (1.4 × 10¹⁶–2.5 × 10¹⁷ m⁻³ s⁻¹) and growth velocity of crystals (2.05 × 10⁻⁹–3.0 × 10⁻⁷ m s⁻¹) in Fe₄₀Ni₄₀P₁₄B₆ glass at temperatures from 653 to 714 K are in reasonable agreement with the experimental data. Possible variations of the established eutectic crystallization mechanism revealed by changes of the Avrami exponent with the heating rate increasing are discussed.