The Non-Isothermal and Isothermal Crystallization Behavior and Mechanism of Fe–Ni Alloys

Abstract

(Fe40Ni40B19Cu1)97Nb3 magnetic amorphous alloys have been prepared by a melt-spun method, and their crystallization behavior and kinetics have been investigated. The results showed that under non-isothermal conditions, the growth process is easier than the nucleation process for both precipitated phases ((Fe,Ni)23B6 and γ­(Fe,Ni)), and the activation energy (E a 2 = 427.03 kJ mol–1) for γ­(Fe,Ni) phase is higher than that of (E a 1 = 275.11 kJ mol–1) for the (Fe,Ni)23B6 phase. Under isothermal conditions, the energy released during the entire crystallization process is independent of annealing temperature, and the crystallization parameters fit with the Kolmogorov–Johnson–Mehl–Avrami (KJMA) model well. The nucleation activation energy (E n ) and growth activation energy (E g ) are 429.2 and 417.2 kJ/mol, respectively. Based on the values of the Avrami exponent n, the transformation process can be divided into three different stages: Stage I, n ≈ 2.5; Stage II, 2.5 ≤ n ≤ 3; Stage III, n > 3. The whole crystallization process from interface-controlled one-dimensional growth converted into interface-controlled three-dimensional growth.

The Isothermal and Non‐Isothermal Growth Behaviors of Ca2Nb2O7 in Molten Slag

“…The Avrami exponent in the JMAK model can provide the dimensions of the growth of crystal and the mechanism of surface nucleation or bulk nucleation. [17][18][19][20][21] But for the process of multiple crystals crystallizing, the JMAK model is not capable of analysis because the crystallization fraction is not clear. The in situ thermal analyzer consisting of a single hot thermocouple, a light microscope, and a photographic system is applied to study the growth behaviors.…”

Amorphous alloys and differential scanning calorimetry (DSC)

“…There are opinions in the literature that the JMAK model has limited validity both in isothermal and non-isothermal conditions [87]. But many improved versions have been published [88,89]. The validity of the Kissinger method is also disputed [90] and therefore authors have further developed the Kissinger method [91,92].…”