Evaluation of hot corrosion behavior of plasma sprayed ceria and yttria stabilized zirconia thermal barrier coatings in the presence of Na2SO4+V2O5 molten salt

In this study, substrates of Inconel 738 LC superalloy coupons were first sprayed with a NiCoCrAlY bondcoat and then with a ceria and yttria stabilized zirconia (CYSZ; ZrO2−25 wt%CeO2−2.5 wt%Y2O3) topcoat by air plasma spraying (APS). Hot corrosion studies of plasma sprayed thermal barrier coatings (TBCs) were conducted in 45 wt%Na2SO4+55 wt%V2O5 molten salt at 1000 °C for 30 h. The results showed that the coating defects, such as pores and microcracks play important roles as effective paths for the salt penetration in hot corrosion. Based on the results, the reaction between molten salt and stabilizers of zirconia (Y2O3 and CeO2), the formation of YVO4, CeVO4 and CeO2 crystals, the detrimental phase transformation of zirconia from tetragonal to monoclinic due to the depletion of stabilizers and finally, the creation of stresses were recognized to be in the degradation mechanism of CYSZ ceramic coatings in the presence of molten sulfate–vanadate salt.