Fig. 1. Schematic illustration for three types of serration flow generally accepted [9].

Fig. 2. Schematic illustration for the quantitative definition method of serrated flow.

Fig. 3. (a) Stress vs. strain curves of specimens tested at temperatures ranging from 523 to 623 K at an applied strain rate of 10?4 s?1; (b) and (c) magnified images of the boxed segments in Fig. 3(a).

Fig. 4. Serration behavior with deformation time at three temperatures.

Fig. 5. Time evolution of strain-rate distribution on the gauge part at three temperatures. The nominal strain rate, $\dot{\varepsilon}^{DIC?L}$, along the tensile direction was evaluated along the central axis of the gauge part by high-temperature DIC and continuously displayed in a serial flow of testing time.

Fig. 6. Strain-rate distribution map showing A-type PLC band propagation in the gauge part of a test piece deformed at 523 K/10?4 s?1, as indicated by the dotted segment in Fig. 5. Each DIC image was acquired at the strain represented by the red circles in the stress-strain curve.

Fig. 7. Strain-rate distribution map showing B-type PLC band propagation in the gauge part of a test piece deformed at 623 K/10?4 s?1, as indicated by the dotted segment in Fig. 5. Each DIC image was acquired at the strain represented by the red circles in the stress-strain curve.

Fig. 8. Strain-rate distribution map showing (A+B)-type PLC band propagation in the gauge part of a test piece deformed at 573 K/10?4 s?1, as indicated by the dotted segment in Fig. 5. Each DIC image was acquired at the strain represented by the red circles in the stress-strain curve.

Fig. 9. Strain-rate distribution map showing C-type PLC band propagation in the gauge part of a test piece deformed at 623 K/10?4 s?1, as indicated by the dotted segment in Fig. 5. Each DIC image was acquired at the strain represented by the red circles in the stress-strain curve.

Fig. 10. Schematic illustration for three types of PLC band propagation and the corresponding serration behavior.

Fig. 11. (a) Map of global strain rate and deformation time. Three temperatures are colored in red for 523 K, blue for 573 K, and green for 623 K. Each serration type is presented by different symbols: squares for A-type, crosses for B-type, circles for C-type, and overlapping symbols for mixed type; (b) map of type transition of serration as a function of the global strain rate.

Fig. 12. (a) Time evolution of PLC band and (b) the corresponding global stress behavior with time as the PLC band evolves at a strain rate of 5.00 × 10?6 s?1. (a) and (b) indicate “jumping” PLC band and typical C-type serrated flow, respectively; (c) time evolution of PLC band and (d) the corresponding global stress behavior with time when the PLC band evolves at a strain rate of 6.25 × 10?6 s?1.

Fig. 13. (a) Time evolution of PLC band and (b) the corresponding global stress behavior with time when the PLC band evolves at a strain rate of 1.00 × 10?5 s?1. (a) and (b) indicate “hopping” PLC band and typical B-type serrated flow, respectively; (c) time evolution of PLC band and (d) the corresponding global stress behavior with time when the PLC band evolves at a strain rate of 1.63 × 10?6 s?1. (c) and (d) indicate “walking” PLC band and typical A-type serrated flow, respectively.