Study of the tensile constrained recovery behavior of a Fe-Mn-Si shape memory alloy

Abstract

Free- and constrained recovery behaviors of a Fe-23.3 Mn-2.8 Si (wt.%) Shape Memory Alloy (SMA) were revealed by uncoiling experiments and tensile tests, respectively. With the enhancement of plastic deformation degree, including by additionally elongating the hot rolled specimens, the increase of the amount of e stress induced martensite (SIM) plates in the detriment if γ austenite, was emphasized by means of optical microscopy and XRD. The tensile-stress variation was analyzed during complex cycling by constrained recovery of the alloy under study, with a tensile strength of 670 MPa and an ultimate strain of 8%. The cycles were composed of: (i) room temperature (RT) loading; (ii) RT partial unloading; (iii) constant strain heating and (iv) constant strain cooling to RT. During the cycles, characterized by average maximum stresses above 500 MPa and recovery stresses above 260 MPa, the observed stress-temperature evolution confirmed the four stage stress variation reported in literature [Z.Z. Dong et al., Acta Mater. 53, 4009 (2005)]. In order to maintain the above stress levels, constrained-recovery strain had to be increased with an average of 1.1% per cycle, between 1 and 3%.