Effects of Ga concentration, heat treatment and deformation temperature on pseudoelasticity of Fe-Ga polycrystals

Abstract

The pseudoelastic behavior of Fe-Ga polycrystals was examined focusing on the effects of Ga concentration, heat treatment and deformation temperature. Fe-Ga polycrystals solutionized at 800°C exhibited pseudoelasticity at room temperature based on reversible motion of 1/4<111> superpartial dislocations dragging an antiphase boundary (APB) in the DO3 superlattice structure. In particular, at and above 25 at%Ga, paired 1/4<111> superpartials dragging the next-nearest-neighbor APB were found to play an important role in the pseudoelasticity. The amount of strain recovery at room temperature was highest at 25 at%Ga. Moreover, heat treatment strongly influenced the pseudoelastic behavior of Fe-Ga alloys. For instance, the Ll 2 and ω-like phases precipitating at higher Ga concentrations led to a decrease in strain recovery since the precipitates suppressed the reversible motion of 1/4<111> superpartials. On the other hand, pseudoelasticity based on twinning and untwinning of 2.2T-type pseudo-twins appeared at low temperatures, especially at - 180°C. The energy of {211} pseudo-twins formed in the Fe-Ga alloys was so high that the twins tended to disappear during unloading resulting in the pseudoelasticity. However, the amount of strain recovery decreased if pseudoelasticities based on dislocation motion and twinning concurrently took place between - 150°C and - 50°C. © 2013 The Japan Institute of Metals and Materials.