CRITICAL ASSESSMENT 1: Outstanding issues in crystallographic variant selection in displacive transformations

Abstract

Variant selection has been a well researched subject in metallurgy and materials science in recent decades. The emergence of experimental techniques capable of determining crystallographic orientation at the grain level has provided insight into the fundamental processes underlying variant selection. The theory, however, is far from complete. Fundamental questions, such as the specific roles of stress and strain in variant selection, have yet to be fully resolved. It remains unclear whether variant selection is a nucleation controlled phenomenon or growth controlled. The possibility of using unconventional forces such as magnetic or electrical fields to influence variant selection is of interest, but needs further research. Any phenomenon related to phase transformation gains importance only when it can be controlled to improve material properties, and it is still unclear how variant selection can be applied to this end. The literature is critically assessed and an attempt is made to identify areas for future research with potential to allow effective application of variant selection.