Fig. 1. (a) The $\bar{B}$o-$\bar{M}$d diagram showing the positions of some developed titanium alloy and newly designed TB17 in this work and (b) a three-dimensional map simultaneously displaying d-electron parameters and [Mo]eq values of TB17 and some other alloys presented in the gray region around the α/α + β boundary in (a).

 Fig. 2(a) displays the morphology and orientation of grains in the as-forged TB17 alloy, which is mainly composed of elongated grains along the deformation direction. The grain size distribution map is shown in Fig. 2(b) and the average value was measured to be about 302 µm based on EBSD data. Fig. 2(c) shows the color-coded kernel average misorientation (KAM) distribution map assessing strain distribution as well as dislocation density of materials [22]. It can be observed that larger strain accumulates near the grain boundaries compared to that inside the grains, indicating heterogeneous KAM distribution in the as-forged sample. The average KAM value calculated by OIM was - 1.22, as given in the Fig. 2(d). The presence of relatively high strain is due to the dislocations slipping and entanglements during the plastic deformation on the one hand, and the transformation strain caused by the precipitation of the α phase from β matrix on the other hand.

Fig. 2. (a) IPF map of the as-forged specimen, the inset is the inverse pole figure, (b) grain size distribution map, (c) KAM distribution map showing a relatively high strain energy and (d) the corresponding fitting curve with calculated average value of 1.22.

Fig. 3. (a) A high-magnified EBSD image showing twelve kinds of α variants within a single β grain of as-forged sample, (b) pole figures from the EBSD point analysis of β matrix, (c) composite pole figures obtained from 12 α variants marked in (a), and (d) individual analysis of 12 α variants.

Fig. 4. (a) XRD diffractograms of the as-forged TB17 alloy, SEM images showing that (b) morphology of elongated grains, (c) continuous αGB precipitating along the grain boundaries and (d) intragranular αf and αs phases inside the matrix, (e) a TEM BF image depicting Widmanstätten structure, the inset shows SAED patterns of αf and β phases along [0$\bar{1}$10] and [$\bar{1}$ 13] zone axes, respectively, and (f) DF image from the (2$\bar{1}$ $\bar{1}$0) diffraction spot indicted by yellow circle in (e).

Fig. 5. (a) STEM-HADDF image of the Widmanstätten structure in the as-forged sample, EDXS elemental maps of the distribution of (b) Ti, (c) Al, (d) Mo, (e) Cr, (f) V, (g) Nb, (h) Zr and (i) Sn.

Fig. 6. EBSD images of (a) phase distribution map, the partition fraction is shown on lower right corner and (b) KAM distribution map displaying a reduction of strain in the beta matrix, (c) a SEM micrograph showing the discontinuous αGB and remained αf precipitates in the ST heat-treated specimen, (d) a TEM BF image indicating an αf lath, (e) the SAED patterns along [1$\bar{2}$1$\bar{3}$] and [$\bar{1}$$\bar{1}$13] zone axes of the α and β phases, respectively, and (f) the TEM dark field image from the marked diffraction (0$\bar{1}$11) spot of α phase.

Fig. 7. (a) STEM-HADDF image of the α lath in the ST sample, EDXS elemental maps of the distribution of (b) Ti, (c) Al, (d) Mo, (e) Cr, (f) V, (g) Nb, (h) Zr and (i) Sn.

Fig. 8. SEM micrographs showing that (a) the precipitates at the grain boundaries and inside the matrix, (b) magnified αf phase and (c) uniform and ultrafine αs phases in the STA specimen, and (d) EBSD KAM distribution map illustrating increased strain after aging treatment in comparison with that of ST sample.

Fig. 9. (a) TEM BF image of α lath containing nano-scale substructures in STA sample, (b) corresponding SAED patterns under the zone axes of [01$\bar{1}$2]α and [1$\bar{1}$ 0]FCC, DF images of (c) HCP α phase and (d) FCC substructures using (2$\bar{1}$ $\bar{1}$ 0)α and ($\bar{1}$ $\bar{1}$ $\bar{1}$) FCC reflections, respectively.

Fig. 10. (a) STEM-HADDF image of the α lath in the STA sample, EDXS elements partitioning maps of (b) Ti, (c) Al, (d) Mo, (e) Cr, (f) V, (g) Nb, (h) Zr and (i) Sn.

Fig. 11. (a) A high-magnification STEM-HADDF image showing the ultrafine FCC substructures in the STA sample, EDXS elemental maps of the distribution of (b) Ti, (c) Al, (d) Mo, (e) Cr, (f) V, (g) Nb, (h) Zr and (i) Sn.

Fig. 12. (a) STEM-HADDF image of the uniformly distributed αs precipitates within the β matrix of the STA sample, EDXS elements distribution maps of (b) Ti, (c) Al, (d) Mo, (e) Cr, (f) V, (g) Nb, (h) Zr and (i) Sn.

Fig. 13. Stress-strain curves of the as-forged and STA specimens with superhigh strength and considerable plasticity at room temperature.

Fig. 14. SEM images showing that (a) the morphology and cracks and (b) magnified dimples and micro-voids in the fracture of STA after tensile testing, SEM micrographs in the section parallel to deformation direction displaying (c) the serrated profile of the crack, the inset is magnified micro-voids presenting around αGB precipitates and (d) transformed microstructures that indicate compatible plasticity in the STA sample after deformation.

Fig. 15. TEM images of αf in the STA sample after tensile test: (a) dislocations slipping and (b) dislocations tangles at two-beam condition of g = [1010], (c) a BF image showing the twins (d) corresponding SAED patterns under the zone axes of [1$\bar{2}$1$\bar{3}$ ]M/T, DF images of (e) HCP α phase and (f) twins using (1$\bar{1}$ 01)M and (1$\bar{1}$ 01)T reflections, respectively.

Fig. 16. Schematic illustrations of the microstructure evolution in the STA sample during deformation (a) dislocation slip in the soft αf phase, (b) dislocation pileups at the αf/β interfaces and in the αf phase, (c) micro-voids nucleation at αGB phase and formation of mechanical twins and (d) crack propagation under severe deformation.