Martensitic transformations in shape-memory alloys: Successes and failures of thermal analysis and calorimetry

Abstract

The development of adapted equipment for high-resolution thermal analysis (thermomicroscopy, acoustic emission, stress-strain and heat conduction calorimetry) provides macroscopically relevant information about the microscopic interactions and the effect of the defects in martensitic transformations of Cu-based shape-memory alloys, e.g., levels of resolution and evolution time scales, intrinsic thermoelasticity, separation between the effects of nucleation and friction. Furthermore, making direct measurements and applying a simple thermodynamic formulation directly relates the friction work (mechanical, analogous to the entropy production) with the width of the calorimetrically calculated hysteresis cycle. Thus, some thermodynamic difficulties found in the measurements and encountered in recent interpretations in the literature are avoided.