Hot Corrosion Behavior of YSZ and CaZrO3/YSZ Composite Thermal Barrier Coatings in Contact with 50V2O5+50Na2SO4 Salts

A novel thermal barrier coating system was formulated to resist hot corrosion environments. In this coating system, 5% CaZrO3 was added to conventional yttria-stabilized zirconia (YSZ). The above composite coating system was compared with the standard YSZ system in the presence of a mixture of 50% Na2SO4 and 50% V2O5 at 950 A degrees C. The results demonstrated that the lifetime of the CaZrO3-added composite system in this highly hostile environment was longer compared with the standard YSZ system. This is due to the fact that the preferential reaction of NaVO3 shifted from yttria to calcia, forming CaV2O4 instead of YVO4. The preferential reactions are discussed in terms of free energy changes and acid-base theory of molten salts with ceramic oxides. Furthermore, calculations of lattice distortion also proved that the CaZrO3-added composite system demonstrated less distortion, thus increasing the overall lifetime of the coating system.