Mapping subgrain sizes resulting from severe simple shear deformation

Grain refinement under interactive effects of severe shear strains, strain rates and temperatures often follows complex trajectories. Encapsulating the process–structure linkages under these conditions is central to controlling product outcomes from processes involving severe plastic deformation. This paper uses in situ characterization of deformation in large-strain machining using high-speed digital image correlation and IR thermography to examine the microstructural consequences across a swathe of directly quantified thermomechanical conditions. Using electron microscopy, it is shown that the average subgrain sizes resulting from this deformation correlate with the strain and the theoretical limit of the subgrain-size that is achievable. From this, a suitably parameterized map-space is proposed for capturing average subgrain sizes resulting from severe shear deformation. The parameterization is characterized by the y axis as the strain and the x axis as a parameter R, which is a function of the strain-rate, temperature and material constants. Noting that the surfaces from machining processes are essentially derived from severe thermomechanical conditions akin to those explored here, the implications of subgrain size-maps for controlling surface microstructures on components manufactured by machining processes are discussed.