Microstructural characterization of thermal barrier coatings on high pressure turbine blades

Thermal barrier coated high pressure turbine blades were characterized befo re and after the service by microstructural analysis and Cr3+ photostimulat ed luminescence piezo-spectroscopy. Thermal barrier coatings, in this study , consisted of electron beam physical vapor deposited yttria partially stab ilized zirconia (YSZ; ZrO2-8 wt.% Y2O3), vapor-deposited aluminide bond coa t and Ni-base superalloy. Compressive residual stress in thermally grown ox ide, measured by Cr3+ photostimulated luminescence piezospectroscopy, was o bserved to be in the order of 2.5 similar to3.0 GPa and varied slightly as a function of substrate geometry. X-Ray diffraction and scanning electron m icroscopy equipped with energy dispersive X-ray spectroscopy were utilized to investigate the microstructural development of thermal barrier coatings. The as-deposited non-equilibrium tetragonal (t') phase in the YSZ coatings was observed to decompose after the service, but the monoclinic (m) phase was only found in the YSZ coatings with concave substrate curvature on the pressure side of the HPT blade. Also, a significant sintering of ZrO2-8 wt. % Y2O3 coating after the service was observed in the microstructure. Locali zed spallation of YSZ occurred within the thermally grown oxide (mostly alp ha -Al2O3) and within the ZrO2-8 wt.% Y2O3 coating for pressure and suction sides of the serviced high pressure turbine blade near the tip, respective ly. (C) 2001 Elsevier Science B.V. All rights reserved.