HOT CORROSION OF CERIA-YTTRIA STABILIZED ZIRCONIA PLASMA SPRAYED THERMAL BARRIER COATING BY EUTECTIC VANDIUMPENTAOXIDE-SODIUM SULFATE

Abstract

The high temperature corrosion behavior of thermal barrier coating (TBC) system consisting of IN-738 LC superalloy substrate, air plasma sprayed Ni24.5Cr6Al0.4Y (wt%) bond coat and air plasma sprayed ZrO2-20 wt% ceria-3.6 wt% yttria (CYSZ) ceramic coat were characterized. The upper surfaces of CYSZ covered with 30 mg/cm2 , mixed 45 wt% Na2SO4-55 wt% V2O5 salt were exposed at different temperatures from 800 to 1000 oC and interaction times from 1 up to 8 h. The upper surface plan view of the coatings were identified for topography, roughness, chemical composition, phases and reaction products using scanning electron microscopy, energy dispersive spectroscopy, talysurf, and X-ray diffraction. XRD analyses of the plasma sprayed coatings after hot corrosion confirmed the phase transformation of nontransformable tetragonal (t') into monoclinic phase, presence of YVO4 and CeVO4 products. Analysis of the hot corrosion CYSZ coating confirmed the formation of high volume fraction of YVO4, with low volume fractions of CeOV4 and CeO2. The formation of these compounds were combined with formation of monoclinic phase (m) from transformation of nontransformable tetragonal phase (t').