June 22-27, 2014
A novel non-destructive inspection technique was developed to measure the residual stresses in TBCs by using Eu3+ photoluminescence piezo-spectroscopy. The relationship between the strongest peak of 5D0→7F2 and stress was determined by the high-pressure experiments and used to evaluate the residual stresses. When the top ceramic coat LZ7C3 in the double-layered coating LZ7C3/YSZ:Eu spalled, the inner YSZ:Eu could produce visible luminescence under UV illumination, providing an indication of the spallation location. The LZ7C3/YSZ:Eu coating spalled bit by bit from LZ7C3 to YSZ:Eu during thermal cycling. The similar thermal expansions of LZ7C3 and YSZ:Eu prolonged the thermal cycling life of the coating.
Xueqiang Cao, "Multilayered thermal barrier coatings" in "Thermal Barrier Coatings IV", U. Schulz, German Aerospace Center; M. Maloney, Pratt & Whitney; R. Darolia, GE Aviation (retired) Eds, ECI Symposium Series, (2015). https://dc.engconfintl.org/thermal_barrier_iv/20