Influence of composition on molten sulfate-vanadate salt corrosion resistance of lanthanum zirconate coatings

Abstract Three lanthanum zirconate (LZO) thermal barrier coatings with designed La/Zr ratios, i.e., 0.7:1 (LZO-7), 1:1 (LZO-10), and 2:1 (LZO-20), are fabricated by laser enhanced chemical vapor deposition and their corrosion resistance in 40 wt% V2O5 + 60 wt% Na2SO4 mixture is studied at 900 °C. The reaction between lanthanum zirconate coatings and NaVO3 produces LaVO4 and ZrO2, which form impediment layer and prevent deeper penetration of the corrosive sulfate-vanadate molten salt. Meanwhile, no severe transverse cracks are found in all the coatings due to the columnar crystalline microstructures. Furthermore, LZO-20 shows the better corrosion resistance than others as the result of the decreased concentration of corrosive molten salts at the contacting interface, which is attributed to the fact that the excess lanthanum consumes maximum NaVO3. Correspondingly, the LaVO4/ZrO2 ratios rise with the increase of lanthanum content. These results uncover the key role of the lanthanum content on the corrosion resistance of the sulfate-vanadate molten salt and are expected to guide the optimization of the future thermal battier coating design by tailoring the composition.