Spraying thermal barrier coatings (TBCs) on engine blades can significantly reduce the temperature of the surface and prevent corrosion and oxidation at high-temperature (Fig1). When the coating material is in service at high temperature, quality problems such as interface cracking and local thinning are prone to occur, which brings safety hazards to the engine system, as shown in Figure 2. Therefore, the real-time detection and evaluation of the state and performance of coating structural materials during preparation and service is of great significance to ensure the safety and reliability of components.

In view of the engineering problems above, the research team studied a one-dimensional thermal diffusion theoretical model based on the direction of coating thickness and established a coating thickness detection method based on the characteristic time of infrared heat map (the moment when the second derivative minimum point appears) by using long pulse thermal excitation. This method overcomes the difficulty of detecting coatings with low thermal conductivity under traditional short pulse excitation. At the same time, this method can realize rapid and large-area coating thickness detection (Fig 3).

Fig    3   Schematic diagram of long pulse excitation thermography in reflection mode

The problem of uneven thickness detection about thermal barrier coatings in long-term service was further studied. The experimental results show that the coating thickness can be detected efficiently and accurately by long-pulse infrared nondestructive testing with the relative error less than 5%, as shown in Fig. 4. At the same time, the influences of thermal excitation duration, infrared sampling rate and coating material parameters are also discussed.

(a)                               (b)

Fig 4 (a) Plot of the curved surface obtained by DIC method and (b) Uneven coating thickness measured by active LPT method

The results were published in NDT&E International, a leading journal in the field of nondestructive testing(Region 1 TOP), with the title of "Non-destructive Evaluation of Uneven Coating Based on Active Long Pulse Thermography". Jiangsu University is the first unit and the corresponding unit. Professor Zhu Jianguo and lecturer Zhuo Lijun of structural Health Management Research Institute are the co-corresponding authors. Graduate student Zhen Huang was the first author. The research was supported by the National Natural Science Foundation of China, the Natural Science foundation of Jiangsu Province and the key Laboratory Foundation of Harbin Institute of Technology.

Paper Links：

https://authors.elsevier.com/a/1f7-p3RA9ST-jE