STEP-WISE MARTENSITE TO AUSTENITE REVERSIBLE TRANSFORMATION STIMULATED BY TEMPERATURE OR STRESS - A COMPARISON IN NITI ALLOYS

In shape memory alloys the thermoelastic martensitic transformation (T MT) can be either thermally induced or stress-induced. The TMT is intr insically step-wise: moreover it has already been shown that an extrin sic fragmentation of thermally induced transformations can be stimulat ed ('step-wise martensite to austenite reversible transformation', SMA RT) by means of incomplete cycles on heating (ICH): the SMART transfor mation shows 'micromemory' features which are reversible. The SMART ph enomenon induced by stress had not yet received great attention and ha s stimulated the present investigations. Several stress-induced SMART key features, similar to the ones found in thermally induced transform ations, are reported for a NiTi alloy. In the stress-induced transform ation SMART, some evidence is given for micromemory effects related to the direct transformation that have no thermal analogue. (C) 1998 Els evier Science S.A.