Comparative study of structures and phase transitions in Fe–(31−35) at% Ga alloys by in situ neutron diffraction

Anelastic Effects in Fe–Ga and Fe–Ga-Based Alloys: A Review

“…Our recent structural studies bring some light to the phase transitions in high-Ga alloys [ 11 , 16 ] and help to interpret anelastic effects in high-Ga alloys. In particular, phase transitions at instant heating for 31–45%Ga alloys were reported using in situ neutron diffraction studies up to 850 °C by Vershinina et al [ 26 , 27 , 135 ], which helps to interpret transient effects in the same alloys related to the appearance of the Fe 13 Ga 9 , α- and β-Fe 6 Ga 5 phases, and to predict new and still unreported anelastic effects. Thus, let us consider Fe–Ga alloys with high Ga content in two steps: alloys below 27–29% and above.…”

“…Quasi equilibrium structure of the alloys after 300 h [ 16 ] and longer annealing time [ 17 ] below 600 °C was reported, and it was shown that even 1800 h of annealing does not allow reaching 100% equilibrium structure due to sluggish diffusion. Phase transitions at instant heating and cooling with the rate ±2 K/min were reported by real-time diffraction experiments for Fe–45%Ga [ 26 ], Fe–38%Ga [ 135 ], and 31–35%Ga [ 26 , 27 , 135 ]. Corresponding TDIF tests with the same heating rate were carried out [ 60 ].…”

“…The transient effect (denoted as P Tr1 in Figure 27 ) earlier assigned to the D0 3 to L1 2 transition moves to lower temperatures (from about 500 °C in alloys with 27–28%Ga to 400 °C in alloy with 38%Ga) and decreases. The reason is the presence of the Fe 13 Ga 9 phase in the structure of the alloys with 32–38%Ga already at room temperature [ 27 ], which leads to the corresponding decrease in bcc-derived phases (D0 3 , B2) and their transition to the L1 2 phase and to a pronounced increase in a volume fraction of the Fe 13 Ga 9 phase above 400 °C which, most probably, contributes to the change of P Tr1 effect temperature and parameters. Structure of the alloy with 38.4%Ga in as-cast state is the mixture of the Fe 13 Ga 9 phase (main phase) and B2.…”

“…Inset to ( b ): the P Tr1 peak height as a function of inverse frequency in Fe–(29–38)Ga); temperature ranges for the existence of phases during heating up to 850 °C ( e ). The vertical segments indicate the temperatures corresponding to significant increase in the volume fraction of Fe 13 Ga 9 upon heating [ 27 ].…”

“…Atomic arrangement from A2 disordered phase to B2 and D0 3 (second-order transition, for both systems) or to L1 2 ordered (through two second-order and one first-order transition in Fe–Ga [ 21 ]) phases affects both the value and the sign of magnetostriction coefficients in Fe–Ga. In Fe–Ga alloys with Ga > 30%, another 3 phases were observed in addition to the B2, D0 3 , and L1 2 : Fe 13 Ga 9 [ 25 ] and α- and β-Fe 6 Ga 5 [ 26 , 27 ].…”