Fig. 1. Inverse pole figure (IPF) maps, GB maps and GB networks topology are shown in (a), (c) and (e) for AM, and (b), (d) and (f) for GM. (g) Fractions (in number) of triple junctions to access RGB networks connectivity in AM and GM. In (a), (b), (c) and (d), RGBs are in black while Σ3, Σ9, Σ27 and other Σ ≤ 29 SBs are colored red, green, blue and yellow respectively. In (e) and (f), RGBs and SBs are represented by black and gray lines.

Fig. 2. SEM micrographs of samples aged at 800 °C for (a) 1 h (c) 12 h of AM and (b) 1 h (d) 12 h of GM.

Fig. 3. TEM micrographs of the η phase precipitated at GB in the AM aged at 800 °C for 12 h (a) and (c). (b) and (d) Diffraction pattern taken from (a) and (c).

Fig. 4. SEM and EBSD results of the η phases precipitated at RGBs in AM aged at 800 °C for (a) 1 h, (b) 12 h, and in GM aged at 800 °C for (c) 1 h, (d) 12 h. RGBs are in black while Σ3 and other Σ ≤ 29 SBs are colored red and yellow respectively.

Fig. 5. SEM and EBSD results of the η phases precipitated at different SBs in GM aged at 800 °C for (a) 1 h, (b) 12 h. RGBs are in black while Σ3, Σ9 and Σ27 are colored red, green and blue respectively.

Fig. 6. SEM and EBSD results of the η phase precipitated at coherent ∑3 in GM aged at 800 °C for (a) 1 h, (b) 12 h. Coherent ∑3 is colored red.

Fig. 7. Statistics of fractions of different boundaries precipitated with η phase in GM after aging at 800 °C for 12 h.

Fig. 8. SEM and EBSD results of AM aged at 800 °C for 12 h. (a) SEM image. (b) Phase map consist of Fe and η phase. (c) Inverse pole figure (IPF) maps indicating the austenite around the η phase has the same orientation as the neighboring grain where growth starts. RGB are colored black.

Fig. 9. Schematic representation of the change in austenite orientation with the formation of η phase.

Fig. 10. SEM microstructures near different grain boundaries in AM after aging at 800 °C for different time: (a) and (b) 1 h at RGB, (c) 1 h, (d) and (e) 12 h at coherent ∑3.

Fig. 11. Secondary ion images show the distribution of (a) Ni and (b) Ti ions in alloy after annealing at 980 °C for 1.5 h.

Fig. 12. SEM maps of the η phase precipitated at (a) connected RGBs in AM, (c) unconnected RGBs in GM, after aging at 800 °C for 12 h. (b), (d) Grain boundary maps corresponding to (a) and (c), respectively. RGBs are in black while Σ3, Σ9 and Σ27 are colored red, green and blue respectively.

Fig. 13. Schematic illustration for formation and growth of η phase. Ti concentration at boundary after solution treatment in (a) AM and (d) GM. Formation of η phase at RGB after short time aging in (b) AM and (e) GM. Growth of η phase precipitated at (c) connected RGB in AM, and (f) unconnected RGB in GM after long time aging. RGBs and SBs are colored black and red, respectively.