The Influence of Structural Defects on the Martensitic Transformation

Abstract
Martensitic single interface transformations, induced by temperature or applied stresses in high resolution apparatus, show an intrinsic thermoelasticity or pseudoelasticity. This phenomenon arises from the interaction of the growing martensite with the preexisting dislocations in the parent phase. The intrinsic thermoelasticity has a great influence on the hysteretic behavior of the transformation, as it prevents the growth of a unique martensite plate. A further increase of the thermodynamically driving force favors the nucleation of new plates. Simulation of the hysteresis loops, when several plates are present, can be performed, in a more realistic way, by considering the various microscopic physical events taking place during the transformation : nucleation of the phases, interaction with the dislocations and stacking faults, number of martensite plates, hysteresis of each plate in single interface 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 becomes larger but decreases gradually with transformation cycling. This behavior can be explained by considering the mechanisms of plastic accommodation of the precipitate in the martensite.