A wide range of complementary research technique - XRD, SEM, TEM, MFM, HV, and low temperature
heat capacity, in situ neutron diffraction, resistivity, vibrating sample magnetometry, internal friction,
dilatometry, and differential scanning calorimetry - is applied to study structure and phase transitions at
heating and cooling of two FeeGa functional alloys with 25 and 27 at.% Ga. Using high resolution neutron
diffraction, it is unambiguously proven that the initial state of both as-cast samples at room temperature
is the D03 phase which results from ordering of the high temperature A2 phase during cooling. Heating
of as-cast samples and their subsequent cooling leads to a cascade of phase transitions which change the
samples’ structural, mechanical and physical properties. These transitions and properties are discussed in
the paper. Transition from metastable D03 to stable L12 phase at heating or isothermal annealing leads to
significant changes in macro (grain size) and micro (ordering) structure, hardness and magnetic properties
(magnetostriction, magnetization). According to our structural studies (ND, XRD), composition Fe-
25.5 at.%Ga below ~600
C belongs to a single phase (L12) range of the equilibrium phase diagram, while
in the Fe-26.9Ga alloy some amount of the D019 phase is also present.