Mapping microstructures from severe plastic deformation in machining

Surface generation by chip formation in machining involves unique Severe Plastic Deformation conditions characterized by superposition of large strains, strain-rates and thermomechanically coupled temperatures. Here, we use plane-strain machining itself as a test of microstructure response to create a knowledge-base of how thermomechanical conditions map to the quantitative characteristics of the deformed microstructure. To accomplish this, the mechanics of the deformation zone are characterized using digital image correlation and infrared thermography, followed by electron microscopy of the resulting chips. Ultimately, we propose Rate-Strain-Microstructure (RSM) map that is parameterized as functions of the strain, strain-rate and temperature, onto which the crystallographic characteristics of the deformed grain structure are projected. The RSM space is characterized by the x-axis as the Zener-Hollomon parameter and y-axis as the effective deformation strain. The implications of resulting mappings for microstructure prediction, control as well as for custom-designing refined surface microstructures, directly using machining are outlined.