Enhanced subsurface grain refinement during transient shear-based surface generation

The present work combines quantitative orientation imaging microscopy and in situ digital image correlation to identify heterogeneities in the coupled mechanics and microstructure evolution occurring in the deformed subsurface during transient shear-based surface generation. Subsurface microstructure exhibited heterogeneities in terms of thickness of the ultrafine-grained layer and recrystallization fraction as a function of position along the surface wavelength. It was observed that subsurface microstructure evolution followed accelerated recrystallization kinetics due to strain path changes occurring in the subsurface during transient surface generation. The magnitudes of these strain path changes and pre-straining of the deformed subsurface were observed to correlate well with changes in the information entropy of the corresponding subsurface crystallographic textures. A phenomenological model for predicting the information entropy of the orientation distribution function based on strain path changes and strain history was formulated and validated for monotonic loading paths. The implications of this generalized framework for modeling and controlling subsurface microstructure in transient surface generation are briefly discussed.