Fig. 1. IPBF-8000 biaxial cyclic testing system. The inset shows the heating facility as well as the water-cooled grips.

Fig. 2. Geometry of the specimens used in uniaxial biaxial tensile tests. (a) Sampling direction within rolled CP titanium sheets, (b) geometry of cruciform specimen, and (c) standard dog bone specimen.

Fig. 3. Microstructure of TA2 titanium observed using an optical microscope.

Fig. 4. Microstructure of TA2 titanium observed using an optical microscope. The inset shows the microstructure of a polished specimen.

Fig. 5. True stress-strain curves for uniaxially and biaxially loaded specimens along (a) RD, (b) TD; θ−σ-σ0.2 curves for uniaxially and biaxially loaded specimens along (c) RD, (d) TD.

Fig. 6. (a) Inverse pole figure maps and (b) pole figures of the as-received material.

Fig. 7. Inverse pole figure maps and twin boundary misorientation maps in (a) area 1 and (b) area 2 of the biaxially deformed TA2 cruciform specimen. Red and green lines indicate {10$\bar{1}$2} extension twins and {11$\bar{2}$2} contraction twins, respectively.

Fig. 8. SEM micrographs for slip trace analysis in (a) area 1 and (b) area 2. The inset shows the contrast between actual slip traces and variant traces of different slip systems calculated by OIM software. Green, yellow, blue, and red thick lines indicate the basal, prismatic, pyramidal Ⅰ, and pyramidal Ⅱ slip traces, respectively.

Fig. 9. Inverse pole figure maps and SEM micrographs for slip trace analysis of TA2 specimens that were biaxially deformed at (a) 300 ℃ and (b) 400 ℃. The inset shows the cross-slip at 300 ℃.

Fig. 10. (a) Changes in the percentages of multiple slip and cross-slip with temperature, (b) changes in the percentages of different slip systems with temperature, and (c) the percentages of M&C at 300 ℃ and 400 ℃.

Fig. 11. Twin boundary misorientation maps and GSF distribution diagrams of the grain matrices with activated (a) {11$\bar{2}$2} contraction twins and (c) {10$\bar{1}$2} extension twins. Inverse pole figures of the orientation of the grain matrices that activate (b) {11$\bar{2}$2} contraction twins and (d) {10$\bar{1}$2} extension twins.

Fig. 12. Bright-field and WBDF TEM images of the specimen biaxially deformed at RT: (a) bright-field image of dislocations with B = [2$\bar{1}$$\bar{1}$0], (b) WBDF micrographs with g = (000$\bar{2}$), (c) WBDF micrographs with g = (01$\bar{1}$0).

Fig. 13. SEM micrographs and GSF distribution diagrams of the specimen biaxially deformed at 400 ℃: for (a) {10$\bar{1}$2} grains and (c) {11$\bar{2}$2} grains. Inverse pole figures of (b) {10$\bar{1}$2} grains and (d) {11$\bar{2}$2} grains.

Fig. 14. SEM micrographs of the specimen biaxially deformed at 400 ℃ for (a) slip trace analysis and (b) cross-slip research. The orientations of the {10$\bar{1}$2} grains are illustrated in (c) the inverse pole figure.

Fig. 15. Schematics showing the process of cross-slip activation in 400 ℃ biaxial deformation. Firstly, (a) prismatic and pyramidal Ⅰ slips are activated and (b) form multiple slip. The self-interaction of multiple slip (c) activated pyramidal slips and (d) cross-slip are generated in stress concentration areas.

Fig. 16. Bright-field TEM images of the specimen biaxially deformed at 400 ℃. (a) The image of dislocations with B = [0001]. The dislocations imaged in two-beam conditions by using the diffraction vectors (b) g1 =($\bar{1}$100), (c) g2 = (01$\bar{1}$0), and (d) g3 = (10$\bar{1}$0).

Fig. 17. (a) Image quality map and (b) inverse pole figure maps for slip trace analysis of TA2 specimens that were biaxially deformed at 300 ℃ for slip trace analysis.

Fig. 18. Schematics of the differences of cross-slip activation under biaxial deformation at (a) 300 ℃ and (b) 400 ℃. Cross-slip traces are marked by red and blue dotted lines.

Fig. 19. Bright-field and WBDF TEM images of the biaxially deformed specimen at 300 ℃, the grain is tilted to B = [01$\bar{1}$0]. (a, c) Bright-field images of <c> dislocations in the two-beam condition with g = (000$\bar{2}$). (b, d) WBDF images of <c> dislocations in the two-beam condition with g = (000$\bar{2}$).