Special Features of L21–L10 Thermoelastic Martensitic Transformations in Ni54Fe19Ga27 Single Crystals in Tension

Abstract

Special features of L21–(14М)–L10 martensitic transformations (MT) are experimentally established for [001]-oriented Ni54Fe19Ga27 (аt.%) single crystals under tensile stress, including staging of superelasticity curves, stress hysteresis, and strain level of martensite formation depending on the test temperature and MT sequence. An additional stage of inelastic strain with high strain hardening coefficient and a stress drop arise on the σ(e) curves in the interval of changes of the stress-induced MT sequence from L21–14M–L10 to L21–L10 (320–400 K) at superelasticity (SE). Special features and physical reasons of this stage and of the stress drop related with the processes of origin and detwinning of L10 martensite during stress-induced L21–L10 transformation are established. The stage of inelastic strain and the stress drop are absent at the L21–14М–L10 MT in the [001]-oriented single crystals or at the L21–L10 MT at other orientations, where detwinning of L10 martensite is suppressed by geometrical reasons.