Influence of Detection Distance on Surface Flaw Depth Evaluation with Ultrasonic Method

Based on the propagation theory of ultrasonic wave in medium and the equivalent method, quantitative evaluation of surface crack depth in laser cladding coating was studied. The results show that ultrasonic wave signal amplitude of surface crack increases gradually with crack depth increasing. After crack depth attains 1.0 mm, signal amplitude of surface crack nearly keeps stable as crack depth increases further. For the same depth, ultrasonic wave signal amplitude of surface crack decreases gradually as detection distance of ultrasonic wave increases, and signal amplitude tends to be stable further. It is assumed that ultrasonic wave energy attenuation caused by anisotropic microstructure and layer interface of laser cladding coating is the main reason for the above results. In order to improve surface crack depth evaluation accuracy, ultrasonic wave energy attenuation caused by microstructure of laser cladding coating is compensated, and the modified approach for surface crack depth of laser cladding coating is proposed and studied.