Fig. 1. Size and processing area of tensile specimen. (a) Size of tensile specimen; (b) processing area

Fig. 2. DPLSP process diagram

Fig. 3. Effect of DPLSP on surface microhardness of Ti6Al4V titanium alloy under different delay time

Fig. 4. Microstructures of surfaces of untreated samples. (a)(b) Areas with low dislocation density; (c)(d) areas with high dislocation density

Fig. 5. Microstructures of surfaces of SPLSPed samples. (a) Dislocation wall; (b) mechanical twins; (c) dislocation cell; (d) refined grains

Fig. 6. Microstructures of surfaces of DPLSPed samples. (a) Dislocation walls; (b) mechanical twins; (c) subgrains; (d) refined grains

Fig. 7. Surface XRD patterns of samples under different treatment methods. (a) XRD pattern; (b) partial enlargement

Fig. 8. Cross-section microhardness values of samples under different treatment methods

Fig. 9. Tensile results of samples under different treatment methods. (a) Stress-strain curves; (b) mechanical properties

Fig. 10. Tensile fracture morphologies and local magnification near surfaces of samples under different treatment methods.

Fig. 11. Schematics of mechanism of DPLSP. (a) Composite structure after DPLSP; (b) one-dimensional tensile stress is transformed into two-dimensional tensile stress