Non-Destructive Testing of Thin Layers by Holographic Sound Field Imaging

Abstract

A technique that involves the holographic imaging of an ultrasound field induced on the surfaces of components and its application to flaw detection are described. Optimum test parameters deduced from tests with artificially produced flaws have been found to give good results when examining protective barrier coatings. The presence of flaws detected in plasma sprayed CoCrAIY and zirconia coatings has been confirmed by metallographic analyses. Good resolution of location, size, and (in the case of cracks) depth has been achieved. The technique should be of use for complex components such as turbine blades since the imaging process is not affected by shape.