Fig. 1. Schematic diagram of ULSP process. (a) LSP device; (b) UP device; (c) laser shock path; (d) ultrasonic shock path

Fig. 2. Surface morphology of specimens under different treatment methods. (a) Untreated; (b) LSP; (c) UP; (d) ULSP

Fig. 3. TEM images of untreated specimen. (a) γ' phase; (b) dislocation

Fig. 4. TEM images of LSP specimen. (a) Grain structure; (b) dislocation; (c) dislocation wall; (d) twinning

Fig. 5. TEM images of ULSP specimen. (a) Grain and subgrain structure; (b) dislocation and γ'' phase; (c) dislocation wall; (d) twinning

Fig. 6. XRD pattern. (a) Complete diffraction curves; (b) local magnification of the main peak

Fig. 7. Microhardness of LSP and ULSP specimens with different laser energies. (a) LSP; (b) ULSP

Fig. 8. Residual stress of LSP and ULSP specimens with different laser energies. (a) LSP; (b) ULSP

Fig. 9. Surface strengthening mechanism of IN718 nickel-based alloy by ultrasonic-assisted laser shock peening

Fig. 10. Microstructure evolution mechanism of IN718 nickel-based alloy by ultrasonic-assisted laser shock peening