MECHANICAL AND ELECTRICAL-PROPERTIES OF A NITI SHAPE MEMORY ALLOY

Mechanical properties of shape memory NiTi alloys have been widely investigated: though a reasonable understanding of the micromechanisms underlying macroscopic behaviour is known, these sometimes can hardly be inferred from macroscopic stress-strain curves. Electrical Resistance (ER) measurements, extensively used to investigate thermal martensite, are here performed on NiTi alloys under stress state. Attention is here focused on the mechanical and electrical behaviour of a NiTi alloy in one start single phase: -in martensitic phase, at T<M(f) or within the hysteresis cycle; -in parent phase, at T>A(f) or within the hysteresis cycle. ER, sensitively affected by electronic structure modifications, lattice structure defects, residual impurities, can profitably be exploited to enlighten similar macroscopic stress-strain behaviour. ER results here obtained allow to discriminate different active micromechanisms, specifically at a same temperature within the hysteresis cycle where similar stress-strain curves are obtained.