Fig. 1. Model of surface wave propagating in a two-layer structure of 45 steel substrate coated with nickel alloy

Fig. 2. Dispersion curves of surface wave on nickel alloy coating with different elastic modulus

Fig. 3. Diagram of laser cladding synchronous powder feeding technology

Fig. 4. Two-layer structure specimen of 45 steel substrate with nickel alloy coating

Fig. 5. Optical microscopy images of nickel alloy coating. (a) Front metallography diagram of the coating; (b) side metallographic diagram of the coating

Fig. 6. Dimensional drawing of tensile samples

Fig. 7. Relationship between stress and strain of tensile test

Fig. 8. Laser ultrasonic testing system

Fig. 9. Schematic of laser ultrasonic signal acquisition region

Fig. 10. Time domain signal diagram and spectrum of the surface at 3 mm distance between the excitation point and the receiving point. (a) Time domain signal diagram; (b) spectrum of the surface

Fig. 11. Dispersion relation of signals collected from region 3 on nickel alloy-coated 45 steel substrate by 2D-FT

Fig. 12. Dispersion curves of different regions by 2D-FT. (a) Dispersion curves of surface wave on regions 1-8 of nickel alloy coating; (b) dispersion curves of surface wave on three regions of 45 steel

Fig. 13. Flowchart for solving the inverse problem of elastic modulus of coating

Fig. 14. Dispersion curve fitting diagram of region 3 of laser cladding coating