Eddy Current Thermographic Method And Its Application In The Nondestructive Test Of Thermal Barrier Coatings

Thermal barrier coatings(TBCs)has complex multilayer structure and service in extremely high temperature environments.The main reason caused the failure of TBCs is disbonding defect in service,therefore,the non-destructive testing of disbonding defect in TBCs is very important.In this paper,eddy current thermography in transmission mode is developed,the non-destructive testing is successfully completed.Firstly,the theoretical analysis is carried out on the disbond defect under heat conduction process of TBC by eddy current thermography in transmission mode.Using finite element method to analysis the thermal response characteristics between the disbond defect area and normal area.Based on the different heat conductivity of disbond defect area and normal area,two kinds of typical thermal response characteristics are summarized and developed.Secondly,the eddy current thermography system in transmission mode is made.Based on the original thermal image characteristics,the adaptive mean carrier algorithm is developed to eliminate the uneven temperature field,reducing the noise of thermal image.In addition,according to the study of interfacial disbonding defects,the new method for disbonding defects is proposed,that is,the interfacial disbonding defect is instead by the ceramic hollow particles.Thermal barrier coatings containing disbonding defects of real turbine blades is made successfully.Non-destructive testing,such as linear laser scanning thermography and eddy current thermography,is applied on the disbonding defect testing.For the linear laser scanning thermography,linear laser carrier algorithm and threshold carrier algorithm are used.For the eddy current thermography,adaptive mean carrier algorithm and Carrier windowing algorithm are used.The thermal response characteristics are highlighted.Finally,the crack defect is detected by the eddy current thermography.The experimental results show that the eddy current thermography can effectively identify 2mm diameter of disbond defect and 0.5mm diameter of blind hole defect,2mm diameter of disbonding defect on the complex curved surface and 50?m width of crack defect.