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

Abstract

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 °C temperature range were recorded: (i) in Fe-27Al the B2 (only in water quenched state) → D03 → B2 → A2, (ii) in Fe-27Ga: D03 → L12 → D019 → A2(B2), and (iii) in Fe-25Ge: D019 (+A2 very limited amount) → A3 (+A2 very limited amount). At continuous cooling from 850 °C, we recorded the following transitions: (i) in Fe-27Al A2 → B2 → D03, (ii) in Fe-27Ga: A2 → B2 → L12 (+ very limited amount of D019 and remaining A2 phases which underwent to D03 ordering), and (iii) in Fe-25Ge A3 (+A2 very limited amount) → D019 (+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, D03) 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 D019 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 D03 → L12 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 D03 ↔ 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.