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 ≥
15ᵒ are marked in black and low angle boundaries with
misorientations from 2ᵒ to 15ᵒ 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.