OXIDATION AND DEGRADATION OF A PLASMA-SPRAYED THERMAL BARRIER COATINGSYSTEM

The isothermal oxidation behavior of thermal barrier coating (TBC) spe cimens consisting of single-crystal superalloy substrates, vacuum plas ma-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 degrees C for up to 200 h. Co ating durability was assessed by furnace cycling at 1150 degrees C. Co atings and reaction products were characterized by X-ray diffraction, field-emission scanning electron microscopy and energy dispersive spec troscopy. No spallation of the ceramic top coatings occurred after up to 200 h isothermal exposure. Interfacial scales consisted of Al2O2 an d Ni(Cr,Al)(2)O-4 spinels. Discrete bands of Al5Y3O12 oriented perpend icular 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 subscal e formation during thermal cycling. Results of the study are in agreem ent with previous findings. This work was the introductory phase of a larger study which will evaluate the oxidation behavior of electron be am-physical vapor deposition (EB-PVD) TBC systems.