The Step-Wise Martensite to Austenite Reversible Transformation Stimulated by a Stress State

Abstract
In shape memory alloys the Thermoelastic Martensitic Transformation (TMT), intrinsically step-wise, can be either thermaliy induced or stress-induced. Moreover, it has already been shown that an extrinsic fragmentation of thermally induced transformation can be stimulated ("Step-wise Martensite to Austenite Reversible Transformation", SMART) by means of Incomplete Cycles on Heating (ICHs) : the SMART transformation shows "micromemory" features that are reversible. SMART phenomenology appears nowadays quite a general property of shape memory alloys : it has been highlighted in several shape memory alloys, notably in NiTi, NiTiCu, NiTiFe, AgCd and CuAlZn. The relevance of the hysteresis cycle width has been nicely correlated with the key features of SMART. SMART phenomenology induced by stress has not yet received great attention and stimulated the present investigation : NiTi wires were used to investigate the micromemory behavior in both thermally induced and stress induced martensitic transformations. Evidence is provided for several stress-induced SMART key features, similar to those found in the thermally induced transformation. In stress-induced SMART, evidence is provided also for micromemory effects related to the direct transformation, with no thermal analogue.