Fig. 1. As-received CP-Ti: (a) EBSD IPF orientation map; (b) grain boundary misorientation distribution; (c) IAMA map showing the distribution of substructured grains (yellow) relative to the deformed (red) and recrystallized (blue) ones; (d) KAM map showing the non-uniformly distributed local misorientations. (c) and (d) were both derived from the EBSD map.

Fig. 2. Schematic diagram of the large volume ECAP system (a) and the processing route (b).

Fig. 3. Schematic diagram of the MDF device and processing routes.

Fig. 4. EBSD/TKD crystal-orientation maps and grain boundary misorientation distributions of CP-Ti after L-ECAP/MDF for different number of passes/cycles: (a) and (b) 8-pass L-ECAP; (c) and (d) 12-pass L-ECAP; (e) and (f) 2-cyc MDF; (g) and (h) 3-cyc MDF.

Fig. 5. TEM micrographs and grain size distribution of the L-ECAP billets: longitudinal plane of 8-pass (a) and 12-pass (c) samples; cross-sectional plane of 8-pass (b) and 12-pass (d) samples; grain size distribution of 8-pass (e) and 12-pass (f) samples.

Fig. 6. Recrystallized nano-grains with iron purities surrounded by the matrix: (a) typical bimodal microstructure; (b) nano-clustered area; (c) EDS results of the matrix; (d) EDS results of the nano-clustered area.

Fig. 7. Bright-field TEM micrographs and grain size distribution for MDF CP-Ti after 2 cycles (a) and (b) and after 3 cycles (c) and (d).

Fig. 8. Uniaxial tensile properties and strain hardening behavior of the as-received and L-ECAP/MDF samples: (a) Engineering stress?strain (σe?εe) curves at a constant displacement rate of 1 mm/min; (b) True stress?strain (σT?εT) curves, converted using standard equations (up to the maximum stress point where non-uniform elongation onsets) from the corresponding curves in (a); (c) Strain hardening rate (Θ = dσ/dε) vs. true strain (εT) curves.

Fig. 9. Microhardness (HV) and yield strength (σ0.2) of the as-received and deformed samples as a function of the inverse square root of average grain size (d-1/2) showing a fit to the Hall-Petch relationship.

Fig. 10. The quantitative description of the average GND density and the driving force for recrystallization during L-ECAP/MDF.

Fig. 11. Grain segmentation by dislocation tangle during the dynamic recovery process and the hexagonal dislocation networks morphology: (a) a segmented grain by dislocation tangles; (b) gradually formed dislocation tangles in a grain; hexagonal dislocation networks formed internal grain (c) and at grain boundary (d).