Fig. 1. (a) Inverse pole figure of the as-received Ti-6Al-3Nb-2Zr-1Mo alloy. Hot-compression bonding and sampling for tensile tests: (b) original square specimens, (c) hot-compression bonding process, (d) schematic describing the sampling position for interfacial microstructure characterization, (e) Sampling scheme of tensile specimens and (f) tensile specimen geometry.

Fig. 2. Three-dimensional (3D) topographies of three types of bonding surfaces: surfaces ground by SiC paper with a grit of (a) #800 and (b) #150, and (c) polished surface. (d-f) Two-dimensional morphologies along the red arrows in (a-c), respectively.

Fig. 3. Orientation imaging microscopy (OIM) and grain reference orientation deviation (GROD) maps for different bonding interfaces with deformation strain of 10% at 850 °C and 1 s-1. (a) OIM and (b) GROD maps for the bonding interface of rough surfaces with roughness of Ra = 0.561 μm (“interface I”); (c) OIM and (d) GROD maps for the bonding interface of rough surfaces with roughness of Ra = 1.481 μm (“interface II”).

Fig. 4. Kernel average misorientation (KAM) maps of (a) “interface I” and (b) “interface II”. Misorientations measured along the lines marked in Fig. 4(b): (c) L1, (d) L2 and (e) L3. The black and white lines represent grain boundaries with different misorientation angles: greater than 15° (HAGBs) and 5°-15° (MAGBs), respectively.

Fig. 5. {0001}, $\left\{ 11\bar{2}0 \right\}$ and $\left\{ 10\bar{1}0 \right\}$ pole figures and the extracted 3D orientation diagrams corresponding to different regions of “interface II” in Fig. 3(b): (a) upper area, (b) lower area and (c) interfacial recrystallization area (X-Y plane is parallel to the cross section of the compression-bonded sample and the Y direction is along the compression direction as described in Fig. 1(d); red indicates the highest density of orientations). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 6. (a) Geometrically necessary dislocations (GNDs) density map and (b) corresponding Euler map of the α phase for “interface I”; (c) GNDs density map and (d) corresponding Euler map of the α phase for “interface II”.

Fig. 7. (a) OIM, (b) KAM and (c) GNDs density maps for the bonding interface of polished surfaces with deformation strain of 10% at 850 °C and 1 s-1 (“interface III”, original bonding interface exists in the form of interface grain boundaries (IGBs)).

Fig. 8. Euler maps of the bonding interfaces of polished surfaces with different deformation strains at 850 °C and 1 s-1: (a) 10%, (b) 15%, (c) 20%, and (d) 30%.

Fig. 9. (a) Stress-strain curves at room temperature for bonding joints of “interface I”, “interface II” and “interface III” compared with base material. (b) Ultimate tensile strength and elongation for base material and bonding joints.

Fig. 10. Tensile fracture morphologies for (a) base material and bonding joints of (b) “interface I”, (c) “interface II” and (d) “interface III”, respectively.

Fig. 11. Schmid factor maps of (a) “interface I”, (b) “interface II” and (c) “interface III” for prismatic slip within α phase.

Fig. 12. Schematic diagram illustrating the proposed rotational dynamic recrystallization (rDRX) mechanism at the original bonding interface of rough surfaces during compression bonding.

Fig. 13. Schematic diagram illustrating the dynamic recrystallization mechanism at the original bonding interface of polished surfaces with increasing deformation strain during compression bonding.