Terahertz Nondestructive Evaluation of Corroding Multilayer Paint Stacks

This paper showcases terahertz nondestructive detection of corrosion buried underneath a multilayer paint stack. Periodically, during the accelerated corrosion protocol, samples are removed from the environmental chambers and characterized using terahertz pulse imaging. Analysis of the reflected waveforms indicates that corrosion leads to a decrease in the amplitude of the deconvoluted pulse, which reflects from the metallic layer. The decrease in amplitude results from a roughening of the metallic surface with corrosion. Surface roughness increases with corrosion, eventually leading to detachment of the multilayer paint stack from the substrate.