Stress measurement of laser cladding coating with critically refracted longitudinal wave method

Based on ultrasonic acoustoelastic theory, stress measurement of laser cladding coating with critically refracted longitudinal wave was introduced. The results show that anisotropic microstructure in laser cladding coating and its interface were main reasons for lower SNR and waveform distortion of critically refracted longitudinal signal. Within elastic limit, the difference in time of flight between critically refracted longitudinal signals increased linearly as the stress increased. When the stress reached 658 MPa, the relationship between difference in time of flight and stress was not obvious as stress increased further. Uneven plastic deformation of laser cladding coating due to anisotropic microstructure caused the above results, and influence degree of uneven plastic deformation on the results increased with the increase of stress. The maximum relative error in stress measurement was about 4.5%. The method in this study can be used to nondestructively measure the stress in laser cladding coating.