Effect of length scales on microstructure evolution during Severe Plastic Deformation (SPD) was studied using orthogonal machining as a test of microstructure response. Machining was performed on Ni-200 in the plane strain configuration inside the chamber of a scanning electron microscope. Mechanics of material flow in the deformation zone was characterized in-situ using Digital Image Correlation. Post-mortem Orientation Image Mapping was performed using Electron Back Scattered Diffraction on partially detached chip specimens. Length scales were varied by setting depths of cut between 10-1 μm. It was found that with shrinking length scales, the continuous evolution of microstructure induced by SPD is replaced by abrupt but sporadic refinement mechanisms. By machining pre-strained samples, it was seen that this switchover is further instigated by initial defect concentrations.

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