Driving Force and Thermal Activation in Martensite Kinetics

A formal kinetics equation derived by the authors in previous work to provide a unified description of martensite transformation is applied to martensite transformation curves obtained with different iron-base alloys under different conditions. In previous work, our formalism was shown to describe athermal as well as isothermal martensite transformation. In this work, it is demonstrated that our unified formalism is able to describe isothermal martensite transformation under depressurization, in the presence of a magnetic field and induced by applied strain. We found that the values of the apparent activation energy fall roughly within an order of magnitude and are compatible with the results reported in the literature. Other important features of martensite transformations, such as, martensite embryos, autocatalysis, and chemical driving force are also discussed. We suggest that our findings are qualitatively compatible with the view that in a favorable environment, austenite can evolve into metastable embryos that are promoted to nuclei, eventually. The embryo→nuclei transition could be regulated by a small barrier overcome by thermal activation.