Oxidation and degradation of a plasma-sprayed thermal barrier coating system

Abstract

The isothermal oxidation behavior of thermal barrier coating (TBC) specimens consisting of single-crystal superalloy substrates, vacuum plasma-sprayed Ni22Cr10Al1Y bond coatings and air plasma-sprayed 7.5 wt.% yttria stabilized zirconia (YSZ) top coatings was evaluated by high-mass thermogravimetric analysis at 1150°C for up to 200 h. Coating durability was assessed by furnace cycling at 1150°C. Coatings and reaction products were characterized by X-ray diffraction, field-emission scanning electron microscopy and energy dispersive spectroscopy. No spallation of the ceramic top coatings occurred after up to 200 h isothermal exposure. Interfacial scales consisted of Al 2O 3 and Ni(Cr,Al) 2O 4 spinels. Discrete bands of Al 5Y 3O 12 oriented perpendicular to the bond coat surfaces were dispersed throughout the alumina scales. Coatings displayed average cyclic lifetimes of 355 1-h cycles. There were indications of interfacial scale delamination and subscale formation during thermal cycling. Results of the study are in agreement with previous findings. This work was the introductory phase of a larger study which will evaluate the oxidation behavior of electron beam-physical vapor deposition (EB-PVD) TBC systems.