Time Domain Terahertz Non-Destructive Evaluation of Aero Turbines

We propose to prove the feasibility of using time domain terahertz (THz) non destructive evaluation (NDE) to inspect turbine blade thermal barrier coatings (TBC). High speed, non contact THz inspection will be useful both during the manufacturing process, during maintaince, and during recoating. Low thermal conductivity ceramic coatings that are deposited on Ni-alloy turbine-engine blades to prevent the extreme thermal conditions in the engine from adversely affecting the blade. These coatings must be applied with proper thickness tolerance, be free of defects, and the air passages must be free of TBC plugs. As the engine experiences thermal cycling and environmental degradation various defects and wear in the TBC will appear. The ceramic layer may decrease in thickness, thermally grown aluminum oxides will appear at the ceramic to bond-coat interface, and voids, coating delaminations, and other effects may occur. In this phase I project, we will investigate quantitatively measuring coating quality parameters by THz NDE. THz is an ideal non contact, non-ionizing, safe, inspection technology for TBC’s, providing high spatial resolution and three dimensional structure. THz NDE can reduce the expense of blade coating manufacturing and enhance safety by detecting issues associated with a blade failure.BENEFITS: A successful Phase II will result in a high speed non contact THz NDE inspection system for turbine blade TBC coatings. This system can be used in the manufacturing process and/or during the inspection of aging engines. During manufacturing, the system can potentially give feedback during the coating process, reducing rework. During inspection, those blades which meet tolerances need not be recoated, while ensuring those blades with defects are recoated. This reduces maintenance costs and enhances safety.