Structure and anelasticity of Fe3Ga and Fe3(Ga,Al) type alloys

The structure of binary Fe-27at.%Ga and ternary Fe-18at.%Ga-6at.%Al alloys is studied after different annealing regimes of as quenched samples. This paper focuses mainly on early stages of different phase transitions: from A2 to D0(3), to L1(2) and D0(19), which decrease functional properties of Fe-Ga alloys. Formation of stable phases goes through formation of metastable phases: according to XRD, the D0(3) ordering of practically disordered A2 solid solution clearly takes place at 150 degrees C, while formation of equilibrium fcc ordered L1(2) phase starts after four hours annealing at 350 degrees C. Upon continuous heating, the transition from D0(3) to L1(2) phase is accompanied by a transient internal friction peak. On its turn, the phase transitions are retarded in the ternary Fe-18Ga-5Al alloy, although a careful TEM study of the ternary alloy proves weak D0(3) ordering in the as-quenched state and formation of small precipitates of L1(2) phase (not detectable by X-ray) after four hours annealing at 275 degrees C. The presence of carbon in studied alloys leads to appearance of Snoek-type relaxation in both binary and ternary alloys: the peak in binary Fe-27Ga alloy is unimodal with activation energy of about 1 eV, and it has hi-modal shape in the ternary alloy Fe-18Ga-5Al with activation energies of about 1.1 and 1.4 eV, corresponding to carbon atom diffusion under stress in vicinity of Ga and Al atoms, respectively. (C) 2015 Elsevier B.V. All rights reserved.