Behavior and mechanism of internal friction peak in quenched Fe-18 at.% Ga alloy

Abstract Quenched Fe-18 at.% Ga with high magnetostrictive properties has a peak (Pwq) in temperature-dependent internal friction (IF) spectrum near 320 oC, which disappears for both as-cast and furnace-cooled alloys. However, the mechanism of this peak is not well understood. In this investigation, the behavior and mechanism of this peak were systematically studied. It is found that the Pwq appears when the sample is quenched from a temperature higher than the critical temperature of the order-disorder phase transition and disappears when annealed at 300 oC for 1 h. The Pwq becomes gradually more apparent as the Ga content increases from below ~18 at.%, and the Pwq almost disappears when the Ga content equals 23 at.%. Combined with deformation and XRD studies, the Pwq does not originate from the vacancies and dislocations produced by the high-temperature quenching process or a phase transition from D03 to L12, and potential formation mechanisms for the Pwq may originate from the transition of Ga-rich Guinier-Preston (GP) zones to D03 structures or lattice relaxation related to Ga-rich GP zones.