High Magnetic Field Effects on Phase Transformation Kinetics of ε-Mn-Al Probed Using Differential Thermal Analysis

Abstract

Differential thermal analysis (DTA) on quenched Mn₅₅Al₄₅ with hcp structure (ε-phase) was performed under magnetic fields up to 15 T in order to investigate the magnetic field effects on the transformation kinetics of ε-phase. So far, the annealing of ε-phase under magnetic field indicated the acceleration of the phase transformation from the ε-phase to the metastable ferromagnetic τ-phase with L1₀ structure and the suppression of the decomposition into the equilibrium phase (β-phase). In this study, as the magnetic field intensity increased, the transformation temperature from ε-phase gradually decreased to the lowest value in the range from 0 to 4 T. A single exothermic peak was observed on each DTA curve, and it was found that the peak contained plural exothermic ε–τ and τ–β transformations. Activation energy of the transformation also showed the lowest value in the magnetic field range from 4 to 10 T, suggesting that the activation energy of the ε–τ transformation decreases at low magnetic field region from 0 to 4 T and the activation energy of the τ–β transformation increases at high magnetic field region from 10 to 15 T. These changes in activation energy were discussed by contribution of Zeeman energy for nucleation of the τ-phase in the ε-matrix and that of β-phase from the τ-phase.

Fig. 7 Activation energy E_a in the function of magnetic field intensity.