Comparative study of structure and phase transitions in Fe-(25–27)%Ga alloys
Résumé
A wide range of complementary research technique - XRD, SEM, TEM, MFM, HV, and low temperatureheat capacity, in situ neutron diffraction, resistivity, vibrating sample magnetometry, internal friction,dilatometry, and differential scanning calorimetry - is applied to study structure and phase transitions atheating and cooling of two FeeGa functional alloys with 25 and 27 at.% Ga. Using high resolution neutrondiffraction, it is unambiguously proven that the initial state of both as-cast samples at room temperatureis the D03 phase which results from ordering of the high temperature A2 phase during cooling. Heatingof as-cast samples and their subsequent cooling leads to a cascade of phase transitions which change thesamples’structural, mechanical and physical properties. These transitions and properties are discussed inthe paper. Transition from metastable D03to stable L12phase at heating or isothermal annealing leads tosignificant changes in macro (grain size) and micro (ordering) structure, hardness and magnetic prop-erties (magnetostriction, magnetization). According to our structural studies (ND, XRD), composition Fe-25.5 at.%Ga below ~600C belongs to a single phase (L12) range of the equilibrium phase diagram, whilein the Fe-26.9Ga alloy some amount of the D019phase is also present.