Research on Ultrasonic Testing Methods for Adhesion Quality of Ceramic Coatings

Ceramic coatings are widely used in aerospace field as thermal barrier materials for their high-temperature performance. The adhesion quality of ceramic coatings on metallic substrate is an important index for coating performance. The uniformity of coating thickness is also important since it determines the thermal stresses in the coatings, which means the coating performance is closely related with the uniformity. The reflection characteristic of the coating-substrate interface is an essential factor for evaluating the adhesion quality. Since the acoustic impedance of ceramic coatings is very close to that of substrate, it is not easy to distinguish their reflection wave in the received waves. In this paper, the propagation characteristics of ultrasonic wave in coatings with different thicknesses on the substrate were researched using immersion ultrasonic testing with pulse-echo method. An algorithm based on the amplitude and phase of reflection waves was proposed for the evaluation of adhesive quality. The results show that, pulse-echo method is highly reliable for the measurement of coating thickness and that the algorithm is effective for the evaluation of adhesion quality of ceramic coatings.

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