Transformation-induced plasticity during pseudoelastic deformation in Ni–Ti microcrystals

Abstract

[1 1 0]-oriented microcrystals of solutionized 50.7 at.% Ni–Ti were prepared by focused ion beam machining and then tested in compression to investigate the stress-induced B2-to-B19′ transformation in the pseudoelastic regime. The compression results indicate a sharp onset of the transformation, consistent with little prior plasticity. Post-mortem scanning transmission electron microscopy reveals no apparent retained martensite but rather a macroscopic band of dislocation activity within which are planar arrays of ∼100 nm dislocation loops involving a single a〈0 1 0〉{1 0 1} slip system. Micromechanics analyses show that the angle of the band is consistent with activation of a favored martensite plate. Further, the stress from the individual variants within the plate is shown to favor activation of the observed slip system. The work done by the applied stress during the B2-to-B19′ transformation is estimated to be ∼34 MJ m −3 at ambient temperature.