Igor S. Golovin

Abstract:

The equilibrium phase diagram does not reflect the real structure of Fe-Ga alloys neither in the as cast state nor after annealing followed by air-cooling or furnace-cooling. Functional properties of the Fe-Ga alloys are extremely sensitive to particular details of the phase transition from the metastable (as-cast, as-quenched) state with A2 or D0₃ structures with positive magnetostriction to the equilibrium state with L1₂ structure and negative magnetostriction. They are also sensitive to short range ordering of the A2 metastable phase including the formation of local martensite-like structures.
In the present study, we have investigated the time-dependence and temperature-dependence of the transition of as-cast metastable Fe-(9-33at.%)Ga ‘Galfenol’ alloys to the equilibrium state along with corresponding changes in their functional properties and anelastic effects that accompany these transitions. To characterize such a time-temperature-transition diagram we used both long-time isochronal annealing (up to 300 hrs) and instant heating treatments with different temperature protocols. In-situ neutron diffraction at instant heating-cooling and isochronal annealing, XRD, DSC, VSM, SEM-EBSD, Mössbauer and mechanical spectroscopy techniques were used to study first and second order phase transitions, structure, and functional properties of Galfenols.

[1] I.S. Golovin, А.M. Balagurov, V.V. Palacheva, I.A. Bobrikov, V.B Zlokazov.
Materials and Design, 98 (2016) 113-119
[2] V.V. Palacheva, A. Emdadi, F. Emeis, I.A. Bobrikov, A.M. Balagurov, S.V. Divinski, G. Wilde, I.S. Golovin. Acta Materialia 130 (2017) 229-239
[3] M.V. Matyunina, M.A. Zagrebin, V.V. Sokolovskiy, O.O. Pavlukhina, V.D. Buchelnikov, A.M. Balagurov, I.S. Golovin. Phase Transitions. 92 (2019) n.2, 101-116