Nondestructive Evaluation and Analysis of Thermal Sprayed Coatings: Latest Technology Progresses and Case Studies

Nondestructive Evaluation and Testing (NDE&T) techniques have been played vital roles in property characterization, process development and quality control of various thermal spray coatings. Besides conventional NDE&T lab methods such as Eddy current thickness measurement and fluorescent penetrant inspection (FPI) for cracking and debonding detection, some latest NDE techniques have been developed, demonstrated and applied to evaluate and characterize thermal sprayed coatings recently. The improved and innovative NDE methods provide more capable and accurate measurement to inspect on surface morphology, 2D and 3D coating porosity, oxide content, cracking and interface debonding, as well as other defects or specific properties. In this work, some latest NDE techniques were investigated and summarized based on several case studies of thermal sprayed coatings. Laser and confocal microscopes had been used for characterizing surface morphologies and roughness profiles of APS and HVOF coatings with 2D and 3D mapping. 2D image analysis and 3D advanced photon source analysis were capable of determining coating porosity percentages, distribution and even morphology. In particular, thermal wave imaging and acoustic micro imaging methods were used to detect the suspicious existence of lateral separation within coating specimens or at the interfaces of coating and substrate.