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(ε) 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.