Fig. 1. (a) Schematic illustration of the submicron sized cylindrical pillars fabricated by FIB milling, (b) pillars used for the in-situ TEM compression tests, and (b1) schematic of the relative positioning of the punch with respect to the pillar.

Fig. 2. (a) Schematic diagram of USRP-processed sample, (b) TEM micrograph of the axial-section of TB8 alloy treated by USRP, (c-c2) the corresponding bright field (BF), dark field (DF) and SAED figures of region V, (A) the fast Fourier transformation image (FFT) of the saffron yellow dashed circle in panel (c), (d-d2) the corresponding BF, DF and SAED figures of region IV, and (e-e2) the corresponding BF, DF and SAED figures of region III.

Fig. 3. (a-a2) The corresponding BF, DF and SAED figures of region II in Fig. 2(b), (b-b2) the corresponding BF, DF and SAED figures of region I in Fig. 2(b), (c) HRTEM image of USRP-processed sample surface, (A) FFT image of the red dashed framed in panel (c), and (d) grain size distribution images of different regions and schematic figure of the gradient microstructure in TB8 alloy processed by USRP.

Fig. 4. XRD patterns for the base material and the USRP-treated TB8 sample.

Fig. 5. In-situ compression tests of samples taken from the gradient structure layer and coarse grained core performed at room temperature. (a) Load-displacement curves obtained at a strain rate of 5 × 10-3 s-1, (b) the engineering stress-strain curve calculated from datum in (a), (c-c2) and (d-d2) pillar images of single crystal and gradient structure extracted from a depth of 3 μm and the corresponding SAED patterns before and after the compression tests, respectively.

Fig. 6. (a-a2) Images of the pillar of gradient structure extracted from the treated surface and the corresponding SAED patterns before and after the compression tests, (b) the HRTEM image of the pillar's surface, (A) and (B) FFT images of the corresponding red dashed frames in panel (b).

Fig. 7. (a) Nano-indentation curves of the base material, at a depth of 3 μm and on the treated surface, (b) the corresponding microhardness and Young's Modulus.

Fig. 8. HRTEM images of the TB8 alloy processed by USRP. (a) HRTEM image of III region in Fig. 2(b), (b) the detail of the yellow dashed framed in panel (a), (e) HRTEM image of II region in Fig. 2(b), (A-I) FFT images of the red dashed framed in panels (a), (b) and (e), (c) and (d) the corresponding IFFT images of B and D zones.

Fig. 9. (a) The detailed image of zone F in (b), (b) HRTEM images of the yellow dashed framed in panel (c), (c) TEM image of region I in Fig. 2(b), (A-G) FFT images of the red dashed framed in panels (a) and (b), (d-d5) the distribution diagrams of Al, Mo, Ti, Nb and Si in the USRP-treated sample surface.

Fig. 10. Schematic illustration of deformation mechanism in TB8 alloy subjected to USRP.