Corrosion of thermal barrier coatings by vanadium and sulfur compounds

Abstract

Hot corrosion studies of two plasma-sprayed coatings, yttria-stabilized zirconia and calcium silicate, were undertaken in order to compare the performance of these materials for use as thermal barrier coatings in high-temperature combustion environments. The coatings were tested in contact with vanadium pentoxide at 1,000°C and, also, under conditions in which they were exposed to sulfur-containing compounds at 900°C or 1,000°C. The samples were subsequently characterized by scanning electron microscopy and X-ray diffraction analysis to identify the effects of these tests on the microstructure and composition. The results indicate that reactions with V2O5 lead to a disruptive phase transformation in zirconia that rapidly degrades the coating. For calcium silicate, the reactions with V2O5 appear to be more limited and less disruptive so that the coating is much more slowly degraded by the vanadium compounds. Exposure to SOx and sulfate salts at high temperature caused rapid degradation of the calcium silicate coatings through a reaction involving the formation of CaSO4. Under similar conditions, the yttria-stabilized zirconia coatings experienced much less attack.