Numerical Analysis of Complex Systems Evolution with Phase Transformations at Different Spatial Scales

This paper shows the existence of a critical dimension for finite length nanowires exhibiting shape memory effects. We give a brief survey of phase transformations, their classifications, and provide the basis of mathematical models for the phenomena involving such transformations, focusing on shape memory effects at the nanoscale. Main results are given for the dynamic of square-to-rectangular transformations modelled on the basis of the modified Ginzburg-Landau theory. The results were obtained by solving a fully coupled system of partial differential equations, accounting for the thermal field, a feature typically neglected in recent publications on the subject when microstructures of nanowires were modelled with phase-field approximations. Representative examples are shown for nanowires of length 2000nm and widths ranging from 200nm to 50nm. The observed microstructure patterns are different from the bulk situation due to the fact that interfacial energy becomes comparable at the nanoscale with the bulk energy.