Fig. 1. Microstructure of solution treated specimen before hot deformation: (a) Orientation imaging microscopy (OIM) map, (b) grain size distribution, (c) misorientation angle distribution, (d) misorientation angle changes along the lines marked L1 and L2. Black and red lines represent grain boundaries with misorientation angle greater than 15° (HAGB) and twin boundary. Colors correspond to crystallographic orientations indicated in inverse pole figure (IPF).

Fig. 2. Experimental flow stress-strain curves and corrected ones for Incoloy 028 alloy deformed at different strain rates within temperature range of 950-1200 °C: (a) 0.001 s-1, (b) 0.01 s-1, (c) 0.1 s-1, (d) 1 s-1, (e) 10 s-1, (f) all flow stress curves and (g) (h) work-hardening rate under different deformation conditions.

Fig. 3. Microstructures of Incoloy 028 alloy hot deformed to a true strain of 0.916 at various deformation conditions: (a) 950 °C, 1 s-1; (b) 1050 °C, 10 s-1; (c) 1050 °C, 1 s-1; (d) 1200 °C, 10 s-1; (e) 1200 °C, 1 s-1; (f) 1150 °C, 0.01 s-1. White, black and red lines represent grain boundaries with misorientation angles: 1～15° (LAGBs), greater than 15° (HAGBs) and twin boundaries, respectively. The IPF indicating the colors correspond to crystallographic orientations is shown for the compression axis (C. A.).

Fig. 4. Recrystallized grain size distribution by various deformation conditions to a true strain of 0.916: (a) 950 °C, 1 s-1; (b) 1050 °C, 10 s-1; (c) 1050 °C, 1 s-1; (d) 1200 °C, 10 s-1; (e) 1200 °C, 1 s-1; (f) 1150 °C, 0.01 s-1.

Fig. 5. Microstructure (a) and changes of misorientation angle along the lines marked by lines L1 and L2 (b) deform at 1050 °C and 10 s-1 to true strain of 0.6. TEM micrographs of the specimen deformed at 1050 °C with the strain rate of 10 s-1 to (c) 0.6, (d) 0.916. The colors and line styles in the OIM micrographs have the same definitions as those in Fig. 3.

Fig. 6. Microstructure (a) and changes of misorientation angle along the lines marked by lines L1 and L2 (b) deform at 950 °C and 1 s-1 to true strain of 0.916. TEM micrographs of the specimen deformed at 1050 °C with the strain rate of10 s-1 to (c) 0.5, (d) 0.916. The colors and line styles in the OIM micrographs have the same definitions as those in Fig. 3.

Fig. 7. Microstructure (a) and changes of misorientation angle along the lines marked by lines L1 and L2 (b) deform at 1150 °C and 0.01s-1 to true strain of 0.35; (c) (d) TEM micrographs of the specimen deformed at 1050 °C with the strain rate of 0.001 s-1 to 0.916. The colors and line styles in the OIM micrographs have the same definitions as those in Fig. 3.

Fig. 8. Microstructure (a) and changes of misorientation angle along the lines marked by lines L1 and L2 (b) deformed at 1200 °C and 0.001s-1 to a true strain of 1.2. The colors and line styles in the OIM micrographs have the same definitions as those in Fig. 3.

Fig. 9. Microstructure (a) and changes of misorientation angle along the lines marked by lines L1 and L2 (b) deform at 1200 °C and 10 s-1 to a true strain of 0.5; TEM micrographs of the specimen deformed at 1050 °C with the strain rate of 0.1 s-1 to a true strain of (c) 0.6 and (d) 0.916; microstructure (e) and changes of misorientation angle along the lines marked by lines L1 and L2 (f) deform at 1100 °C and 1s-1 to a true strain of 0.6. The colors and line styles in the OIM micrographs have the same definitions as those in Fig. 3.

Fig. 10. Relationship between Zener-Hollomon parameter and (a) stress, (b) strain at peak or θmin, (c) relationship between σ at strain of 0.916 normalized by shear modulus (σ/G) and DDRX of Incoloy 028 alloy.

Fig. 11. The fraction of DRX, LAGBs and HAGBs at different strains in the (a) high flow stress region (1050 °C, 10 s-1), (b) low flow stress region (1150 °C, 0.01 s-1) and (c) moderate flow stress region (1100 °C, 1 s-1).

Fig. 12. Schematic diagram of the DRX mechanism transition under different deformation temperatures and strain rates of Incoloy 028 alloy.