Fig. 1. (a) Schematic of the HE-XRD measurement set-up. (b) Representative X-ray diffraction pattern (quarter of image plate) of the as-ARBed N8 composite. RD: rolling direction, ND: normal direction, TD: transverse direction.

Fig. 2. The measured and the CMWP fitted diffraction profiles of (a) N1 and (b) N8 composites. The measured and the fitted diffraction data is shown with black circles and solid red lines, respectively. The difference between the measured and the fitted spectra is shown with solid blue lines. The diffraction intensity and the difference are shown in logarithmic and linear scale, respectively.

Fig. 3. Evolution of dislocation activities for (a) various Burgers vectors and (b) the five common slip systems with ARB cycles in Ti of the ARBed Ti/Nb composites. (c) Schematic illustration of the Burgers vector direction of each dislocation type and common slip planes in the hcp structured Ti. The fitted lines in (a) and (b) are regression lines with 95% confidence to show the variation tendency. The dislocation activities obtained from the X-ray peak profile analysis of a CP-Ti under hot rolling [39] are shown as dashed lines in (a), in which the equivalent true strains of processing are indicated in the upper abscissa axis. B<a>: basal 〈a〉 slip, P<a>: prismatic 〈a〉 slip, Py<a>: pyramidal 〈a〉 slip, PyI<c+a>: first-order pyramidal 〈c+a〉 slip, PyII<c+a>: second-order pyramidal 〈c+a〉 slip. SBs: shear bands.

Fig. 4. Representative lamellar morphologies of (a) N5 and (b) N8 SBL Ti/Nb composites showing the initiation of shear bands. The yellow arrows and boxes indicate the necking of the hard Nb layers and the formation of shear bands that cut through several heterophase interfaces, respectively. The Ti layers are shown in dark grey and the Nb layers are in light grey, respectively.

Fig. 5. Dislocation characteristics in Nb layers. The representative modified Williamson-Hall plots with different dislocation activities of Nb in the (a) N1 and (b) N8 composites. Here, the broadening of each peak, ΔKhkl, is plotted as a function of ($K_{h k l} \bar{C}_{h k l}^{1 / 2}$), where Khkl corresponds to the peak position and $\bar{C}_{hkl}$ is average dislocation contrast factor of the {hkl} plane. E1: {110}〈$1\bar{1}1$〉 edge dislocation, E2: {112}〈$11\bar{1}$〉 edge dislocation, S: screw dislocation, Mix: a combination of 88% E1 and 12% E2 dislocations.

Fig. 6. Textures characterized by neutron diffraction. Pole figures of (a) N2, (b) N5 and (c) N8 Ti/Nb composites after intermediate annealing (AN). The left and right columns are pole figures for Ti and Nb, respectively. The orange stars are projections of the orientations with the maximum orientation distribution function (ODF) intensity. RD: rolling direction, TD: transverse direction, ND: normal direction.

Fig. 7. Schematic illustration of the grain orientations with Euler angles of (173°, 34°, 186°) in Ti and (328°, 0°, 347°) in Nb, and the corresponding configuration of slip planes, illustrating the local strain accommodation between Ti and Nb at heterophase interfaces. Displacement gradient tensor (e) expressed in the slip reference system is also given. RD: rolling direction, TD: transverse direction, ND: normal direction of the ARBed sheets. b: Burgers vector, n: normal direction of slip plane. shcp and sbcc denote theoretical slip shear of the slip systems in the hcp structured Ti and the bcc structured Nb, respectively.

Fig. 8. TEM characterizations of dislocations in the SBL composite. Bright-field TEM of the dislocation structures for (a) the as-ARBed N8 composite and (b) the N8 composite after the subsequent uniaxial tensile testing to fracture (with a maximum elongation of ～9%). Dislocations that are visible under imaging vector g=[0002]* are 〈c+a〉 dislocations based on dislocation invisibility criterion g·b=0 (b: Burgers vector). The inset in the right panel of (b) shows the various crystallographic plane traces, enabling the determination of crystal planes of the observed 〈c+a〉 dislocations, as shown by the short-dashed lines. B: basal plane, P: prismatic plane, PyI: first-order pyramidal plane, PyII: second-order pyramidal plane.

Fig. 9. Superior mechanical properties of the SBL composites. (a) Engineering stress-strain curves of the SBL Ti/Nb composites processed by five and eight ARB cycles (N5 and N8 composites) in comparison with other LMCs composed of at least one hcp constituent [[48], [49], [50], [51], [52], [53], [54], [55], [56], [57], [58], [59], [60], [61]]. ε denotes equivalent true strain achieved in the fabrication routes of rolling or ARB processing. (b) Comparison of ultimate tensile strength versus elongation to fracture obtained in the current Ti/Nb composites with other materials. (c) Fracture elongation versus equivalent true strain applied in mechanical processing of the materials. All data are obtained from uniaxial tensile tests along the rolling direction with nominally quasi-static strain rates at room temperature.