Time temperature transition and effect of thermocycling (D03 ↔ L12) on Fe3Ga-type alloy structure

An analysis of the first order transition kinetics between D0₃ and L1₂ phases in Fe₃Ga-type alloy is carried out. Structure and magnetostriction of the samples were carefully controlled by SEM-EBSD analysis and magnetostriction tests after different heat treatments, and additionally in in situ regime by VSM and DSC. C-shaped curves for time-temperature-transition (TTT) diagram based on the results of the EBSD analysis of Fe-27Ga alloy are constructed in the temperature range between 400 and 550 °C. TTT diagram shows that the nucleation rate for L1₂ phase increases in the sequence 400 → 475 → 550 °C, while the growth rate reaches a maximum at about 500–525 °C. Effect of D0₃ ↔ L1₂ thermocycling on the kinetic of the D0₃ → L1₂ transition is studied for the first time. The amount of the L1₂ phase after sample re-quenching and subsequent annealing at the same annealing temperature and time, significantly increases compared with the first cycle quenching and subsequent annealing, demonstrating memory effect of previous transitions.