Study On Eddy Current Nondestructive Testing Of Multicoating Thickness And Its Realization

With the rapid development of science and technology and the constant improvement of the aerospace vehicle speed, high-speed aerospace craft and turbine engine blade coating materials and structure of the coating become more and more complex. However, the thickness and uniformity of the coating will directly affect the temperature distribution in the substrate. Uneven thermal barrier coating thickness can cause a rapid increase of the local temperature in the substrate. It can cause the failure or the state of motion changes of turbine engines and aircraft parts, seriously even can cause catastrophic accident. Therefore, non-destructive evaluation of multi-layer conductive coating thickness has become an important research topic in high-end equipment manufacturing industry.Eddy current nondestructive testing technique, with its characteristics of low cost, high sensitivity, fast detection and non-contact measurement, has been widely used in aerospace, nuclear industry and other fields. Supported by the SAST fund of Academy of China Aerospace Science and Technology Group VIII, this paper carried out the experimental research on multi-layer conductive coating thickness measurement using eddy current testing. The main contents of this paper are as follows:(1) According to the bases principle of eddy current testing and multi-frequency multi-parameter detection theory, the multi-frequency eddy current testing system for coating thickness test is designed. The excitation signal source, signal conditioning circuit, the design and selection of data acquisition module data processing program are included in the system.(2)The interaction between layers of coatings is studied by using the experiment testing platform. According to the experimental results, a new approach for detecting multi-coating thickness is proposed. And the effects of different detection parameters on the test results are analyzed, such as excitation frequency and signal amplitude, structural parameters of excitation coil and magnetic testing components, and the conductivity of coating. Finally the optimal testing conditions for multi-layer coating thickness testing are obtained.(3)The single layer coating, double layer coating and three layer coating on the substrate and unknown conductivity coating thickness are measured. Then the detection system is optimized according to the actual test conditions and the error analysis.By combining the experiment research and the improved experiment testing system, the feasibility of polygon method in precise detecting multi-coating thickness areas is verified.