THE INFLUENCE OF STRUCTURAL DEFECTS ON THE MARTENSITIC-TRANSFORMATION

Martensitic single interface transformations, induced by temperature o r applied stresses in high resolution apparatus, show an intrinsic the rmoelasticity or pseudoelasticity. This phenomenon arises from the int eraction of the growing martensite with the preexisting dislocations i n the parent phase. The intrinsic thermoelasticity has a great influen ce on the hysteretic behavior of the transformation, as it prevents th e growth of a unique martensite plate. A further increase of the therm odynamically driving force favors the nucleation of new plates. Simula tion of the hysteresis loops, when several plates are present, can be performed, in a more realistic way, by considering the various microsc opic physical events taking place during the transformation: nucleatio n of the phases, interaction with the dislocations and stacking faults , number of martensite plates, hysteresis of each plate in single inte rface condition and interaction between the plates. The interaction of the martensitic transformation with small precipitates also produces an important influence on the hysteretic behavior: the hysteresis beco mes larger but decreases gradually with transformation cycling. This b ehavior can be explained by considering the mechanisms of plastic acco mmodation of the precipitate in the martensite.