The microstructural observations of the samples deformed by both deformation modes are shown in Fig. 3. Fig. 3 (a-e) shows microstructure of monotonous (CW) deformed specimens and Fig. 3 (f-j) shows microstructure of (CW-CCW) deformed specimens at ԑ=1,4,12,24,60 respectively. The variation in the average grain size and fraction of HAGBs w.r.t strain is plotted in Fig. 4 (a & b) for monotonically deformed specimens and strain reversal deformed specimens respectively. The high angle grain boundaries having misorientations θ ≥ 15 are marked in black and low angle boundaries with misorientations from 2 to 15 are marked in red.
Observation from Fig.3 (a-e) reveals that there is a continuous evolution of structure from LAGBs at lower strain to heterogeneous structure consisting of LAGBs and HAGBs at an intermediate strain level and ultimately resulting in an equiaxed ultrafine grained structure separated by mostly HAGBs. The microstructure evolution in case of strain reversal deformation (Fig. 3 (f-j)) is similar to the monotonous deformed specimens, where at starting LAGBs were found to dominate which then ultimately transforms to ultrafine grained structure at higher strains.