Hot corrosion behaviors of gas tunnel type plasma sprayed La2Zr2O7 thermal barrier coatings

Gas tunnel type plasma sprayed free-standing La2Zr2O7 coating specimens with a thickness of 300–400 μm were prepared under optimized operating conditions and were subjected to hot corrosion test in the presence of corrosive impurities such as V2O5, Na2SO4, and Na2SO4 + V2O5 mixtures (60:40 wt%) at two different temperatures for duration of 5 h, i.e. 1000 and 1350 K for V2O5 and Na2SO4 + V2O5 mixtures, 1200 and 1350 K for Na2SO4. For temperatures at 1350 K, the reaction mechanism of V2O5 and the mixture of Na2SO4 + V2O5 are similar and LaVO4 is formed as the corrosive product, which leads to massive phase transformation from pyrochlore to tetragonal and monoclinic phases. Microstructural observations from planar reaction zone (PRZ) and melt infiltrated reaction zone (MIRZ) reveals that the present La2Zr2O7 coating exhibits good hot corrosion resistance in V2O5 environment and moderate for the mixture of Na2SO4 + V2O5, but is worst in Na2SO4 environment.