Abstract
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.
Highlights
Metallic materials, especially steels and aluminum alloys, are the most widely-used engineering materials in the society for their excellent comprehensive mechanical properties
In certain extreme conditions, such as high temperature, strong corrosion and wear, etc., ceramic materials perform better than traditional metallic materials
In order to enhance the performance of metallic materials in extreme conditions mentioned above, ceramic materials are usually sprayed or bonded on the surface of metallic substrate as coatings [1, 2]
Summary
Especially steels and aluminum alloys, are the most widely-used engineering materials in the society for their excellent comprehensive mechanical properties. In order to enhance the performance of metallic materials in extreme conditions mentioned above, ceramic materials are usually sprayed or bonded on the surface of metallic substrate as coatings [1, 2]. In Maxwell model, the adhesive is considered as a spring and a damper in series and is usually used to describe stress relaxation. While in Voigt model, a spring and a damper in parallel and is usually used to describe creep. For the model of interface of sample, Tattersall [8] proposed a spring-based model In his model, the interfacial forces are represented by a density of springs between the two media and the springs are light enough to transmit stress instantaneously across the boundary. Singher [9] regarded the interface between adhesive and adherend as a spring-mass structure, and proposed a quasi-static approach, in which a density of springs with constant stiffness were used to describe the shear mechanical behavior of the interfacial adhesive-adherend
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