Fig. 1. Stages of grain refinement in single-phase low SFE materials: (a) primary twinning, (b) secondary twinning and development of LAGBs in primary twins, (c) shear banding which fragments twins, and (d) evolution of LAGBs into fine grains.

Fig. 2. EBSD maps for AB after ECAP at 350 °C for 4 passes via route C, showing (a) highlighted refined grains (blue) and twins (red), and (b) grain misorientation. HAGBs, LAGBs and twin boundaries are indicated as black, grey and red lines, respectively, with incoherent twin boundaries indicated as green lines in (a). Arrowed and numbered features are described in the text.

Fig. 3. EBSD map for AB after ECAP at 400 °C for 4 passes via route C, showing (a) highlighted twins and refined grains and (b) grain misorientation. Lines and shading have the same meaning as in Fig. 2, with arrowed and numbered features described in the text.

Fig. 4. SEM microstructures of NAB in (a) the as-received state containing lamellar κIII (arrow 1), fine κIV particles (arrow 2), and coarse κII particles (arrow 3), and after ECAP via route BA at 400 °C for (b) 1 pass which induces fragmentation (arrow 1), buckling (arrow 2) and spheroidization of the lamellae (3), with further refinement after (c) 2 passes, and (d) 4 passes.

Fig. 5. EBSD maps for the as-received NAB showing (a) highlighted twins and refined grains, and (b) grain misorientation. κ phases excluded due to scale, and lines and shading have the same meanings as in Fig. 2.

Fig. 6. EBSD maps for NAB after 1 pass at 400 °C showing highlighted refined grains and twins. Different microstructural regions are highlighted including (a) an overview of the different particle types, and closer views of the boundary structures around (b) the fine κIV, (c) fragmented lamellae, and (d) buckled lamellae. Lines and shading have the same meanings as in Fig. 2, with the κ phases shaded dark grey. Arrowed, numbered, and circled features are described in the text.

Fig. 7. EBSD misorientation maps for NAB after 1 pass at 400 °C showing the same microstructural regions described in Fig. 6. κ-phases are highlighted light blue, with HAGBs between κ-phases indicated by black lines and LAGBs dark blue. Line colours in the α-phase have the same meaning as in Fig. 2.

Fig. 8. EBSD maps for NAB after ECAP at 400 °C via BA showing highlighted refined grains and twins (left) and misorientation data (right) after (a-b) 2 passes and (c-d) 4 passes. Lines and shading have the same meanings as in Fig. 6, Fig. 7, with arrowed and numbered features described in the text.

Fig. 9. EBSD maps for NAB after 4 passes of ECAP via BA showing highlighted refined grains and twins (left) and misorientation data (right) at pressing temperatures of (a-b) 450 °C and (c-d) 500 °C. Lines and shading have the same meanings as in Fig. 6, Fig. 7, with arrowed and numbered features described in the text.

Fig. 10. Stages of grain refinement in single-phase low SFE alloys at elevated temperatures: (a) reduced density of twins with LAGB segments, (b) detwinning and deformation to existing twin structures leading to incoherent twin boundaries, (c) secondary twinning, shear banding and dynamic recrystallisation at deformed twins, and (d) propagation of recrystallised grains at shear bands and deformed twins. Arrowed and numbered features are described in the text.

Fig. 11. Mechanisms and structures around particles of different sizes: (a) secondary slip by prismatic looping around fine particles leading to (b) cellular structures; (c) deformation zones around coarse particles leading to (d) rings of recrystallised grains.

Fig. 12. Various stages of cross-slip and twin formation in the presence of fine particles, showing (a) prismatic looping into alternative slip directions, (b) formation of a twin nucleus on the primary slip plane following saturation of prismatic looping, and (c) expansion of a twin boundary beyond the bounding particle.

Fig. 13. Dependence of substructure formation on the crystal and lamellar orientations, showing (a) twins (grey shaded) and twin nuclei (solid lines) when the ECAP shear plane (bottom left to top right), slip plane (arrowed) and lamellar planes (black shaded) are aligned, or sub-cell formation when either the lamellae (b) or slip direction (c) are misaligned with the shear plane.

Fig. 14. Formation of HAGBs between fragmented lamellae, showing (a) initial deformation altering the crystal orientation on both sides of the lamellae through lattice rotation or twin formation, and (b) creation of new boundaries (thick black line) after the fracture of the lamellae.