Fig. 1. Experimental setup of ultrasonic vibration assisted laser cladding

Fig. 2. (a) Digital speckle pattern generation principle; (b) Digital speckles; (c) Speckle pattern of substrate surface after laser marking

Fig. 3. (a) Random speckle patterns R₁, R₂, R₃ generated by Python; (b) SSIM* under different subarea division

Fig. 4. (a) Speckles for testing; (b) Visualization results of autocorrelation function

Fig. 5. (a) Periodic speckle pattern A₁-A₅ and random speckle pattern A₆ generated by Python; (b) Calculation results of SSIM* and A_n; (c) Calculation results of MIG and MIG_OP

Fig. 6. Speckle patterns taken in the experimental environment T₁-T₄

Fig. 7. Strain field before and after 1 s under ultrasonic vibration. (a) Strain field in the x direction; (c) Strain field in the y direction

Fig. 8. The strain contours in x and y directions during the cladding process under different ultrasonic powers. (a1), (a2) Without ultrasonic vibration; (b1), (b2) With ultrasonic power of 500 W; (c1), (c2) With ultrasonic power of 1000 W; (d1), (d2) With ultrasonic power of 1500 W; (e1), (e2) With ultrasonic power of 2 000 W; (f1), (f2) With ultrasonic power of 2 500 W

Fig. 9. (a) The strain distribution on M-M′; (b) The strain distribution on N-N′; (c) Strain standard deviation under different ultrasonic power

Fig. 10. The distribution of P₁, P₂ and P₃ points

Fig. 11. The strain changes of P₁, P₂ and P₃ points with time under the action of ultrasound and without ultrasound. (a) y direction strain; (b) x direction strain

Fig. 12. High-speed camera images with and without ultrasonic vibration. (a1)-(a3) Without ultrasonic vibration; (b1)-(b3) With ultrasonic vibration

Fig. 13. SEM of cladding layer with and without ultrasonic vibration. (a), (c) Without ultrasonic vibration; (b), (d) With ultrasonic vibration

Fig. 14. SEM local magnification and elemental analysis. (a) Without ultrasonic vibration; (b) With ultrasonic vibration; (c) The content of several elements in B₁, B₂ and B₃ fractions