Degradation of YSZ/EUCOR TBC Coating System during High Temperature Low Cycle Fatigue Tests

摘要

Thermal barrier coatings are widely used to protect the substrate from high temperature and extremely aggressive environments in gas engines. In the present article, authors have been studied degradation of complex thermal barrier coating system deposited on polycrystalline nickel superalloy IN 713LC. The substrate material was grit blasted with alumina (Al_2O_3) particles prior to air plasma deposition of CoNiCrAlY bond coat. Top coat consists of conventional zirconia (ZrO_2) stabilized by yttria (Y_2O_3) -YSZ ceramic in combination with a eutectic nanocrystalline ceramic Eucor made of zirconia (ZrO_2), alumina (Al_2O_3) and silicia (SiO_2) -in the ratio of 50/50 in wt. %. The top coat was deposited using water stabilized plasma. Test specimens with the TBC coating system were fatigued under strain control condition in fully reversed symmetrical push-pull cycles at 900°C in air. The microstructure of TBC was characterized with scanning electron microscopy and energy dispersion X-ray analysis. The coating hardness and thickness were measured. Fracture surface and polished sections parallel to the specimen axis were examined to study damage mechanisms in coatings under cyclic loading at high temperature. TBC delamination was observed at the top coat/bond coat interface after cyclic loading at high temperature. Fatigue crack initiation sites are documented. Majority of fatigue cracks start from the surface and top coat/bond coat interface.