Application of pulsed thermography to quality assurance of thermal barrier coatings

Abstract

Thermal barrier coatings (TBCs) are applied on components which need to withstand high temperatures in furnaces and turbines. The coatings are generally yttria stabilized zirconia which are applied to the surface of components by a plasma spray process. In order to provide oxidation resistance the metal surfaces are normally treated with an aluminium-rich MCrAlY bond coat which will form a stable oxide during service at elevated temperatures. Pulsed thermography is a technique which consists of applying a fast and short burst of heat to a specimen and then monitoring the thermal evolution of the surface by means of an infrared camera. This paper describes the application of pulsed thermography on a ‘blind test’ of sprayed TBCs on real turbine components. The study validates the usefulness of pulsed thermography as an additional quality assurance tool prior to placing coated components into service.