Structure induced anelasticity in Fe3Me (Me = Al, Ga, Ge) alloys

Neutron diffraction and mechanical spectroscopy techniques were combined in one study in order to interpret structure induced anelasticity of Fe-(25-27) Me alloys where Me is Al, Ga or Ge. The following sequences of phase transitions at continuous heating in the 20-850 degrees C temperature range were recorded: (i) in Fe-27Al the B2 (only in water quenched state) -> D0(3) -> B2 -> A2, (ii) in Fe-27Ga: D0(3) -> L1(2) -> D0(19) -> A2(B2), and (iii) in Fe-25Ge: D0(19) (+A2 very limited amount) -> A3 (+A2 very limited amount). At continuous cooling from 850 degrees C, we recorded the following transitions: (i) in Fe-27Al A2 -> B2 -> D0(3), (ii) in Fe-27Ga: A2 -> B2 -> L1(2) (+very limited amount of D0(19) and remaining A2 phases which underwent to D0(3) ordering), and (iii) in Fe-25Ge A3 (+A2 very limited amount) -> D0(19) (+A2 very limited amount). These transition sequences determine different temperature dependencies of magnetic and anelastic properties in the studied alloys. In Fe-27Al and Fe-27Ga water quenched samples the bcc-born phases (A2, B2, D0(3)) dominate at room temperature and a Snoek-type anelastic relaxation is recorded in both alloys. The Snoek relaxation is not recorded in Fe-25Ge alloy which has a close-packed D0(19) structure. Zener relaxation was recorded in all three systems Fe-Al, Fe-Ga and Fe-Ge both at heating and cooling. The first order irreversible D0(3) -> L1(2) transition (in Fe-27Ga) at continuous heating generates internal stresses due to a huge jump-like increase of atomic volume with temperature and leads to a well-pronounced transient internal friction effect. The reversible D0(3) <-> B2 transition (in Fe-27Al) also leads to a transient but much smaller anelastic effect. Much slower phase transition in Fe-25Ge alloy does not influence temperature dependent anelasticity in this alloy. (C) 2016 Elsevier B.V. All rights reserved.