Study On The Stability Of LnPO₄ TBC Materials In Salt Corrosion Environment At High Temperature

Thermal Barrier Coatings?TBCs?technology is one of the key factors to reduce the working temperature of the hot section in turbine engine blade.The service condition of TBCs is the worst among hundreds of functional coatings and the selection of the materials for TBCs is aboselutely harsh.The excellent characteristics of LnPO₄?Ln=Sm,Gd?make it become extremely promising candidate for TBCs.TBCs has a wide range of failures,and the high temperature attack caused by CMAS and molten salts are the most destructive,meanwhile they are also vary difficult to control.In this study,the resistance characteristics of LnPO₄?Ln=Sm,Gd?to CMAS attack were investigated and the related mechanisms were discussed,which could provide the foundation for developing new TBCs for ultrahigh temperature application.LnPO₄?Ln=Sm,Gd?ceramic powders were synthesized by chemical route and calcination method and then cold pressed into disc compacts.CMAS with a composition of 24CaO-20MgO-8Al₂O₃-48SiO₂ in mole ratio was used in this study prepared by mechanical ball-mixing method.The CMAS was dropped on the surface of LnPO₄ bulk by liquid method and then the LnPO₄ bulk with CMAS was heat treated for investigation of resistance characteristics of LnPO₄ to CMAS attack.The results showed that CaAl₂Si₂O₈,MgAl₂O₄ and Ca₃Ln₇?PO₄??SiO₄?₅O₂ were produced during the reaction between CMAS and LnPO₄.The reaction layers composed of these three products was formed to suppressing CMAS infiltration.The resistance characteristics of GdPO₄ was better than that of SmPO₄.LnPO₄?Ln=Sm,Gd?ceramic powders were synthesized by chemical route and calcination method and then cold pressed into disc compacts.Analytical pure V₂O₅powder was deposited on the surface of LnPO₄ bulk and then the LnPO₄ bulk with V₂O₅was heat treated in muffle for 2h and 10h,respectively,to investigate resistance characteristics of LnPO₄ to V₂O₅ attack.The results showed that the reaction between V₂O₅ and LnPO₄ is extremely weak and the reaction product?LnVO₄ and Ln₄?P₂O₇?₃?is few in number.Plenty of molten V₂O₅ fully penetrated into the LnPO₄ bulk,but the structure of inner LnPO₄ bulk was not destroyed.No crack or defect was found in bulk,which indicated the stability of LnPO₄ under the V₂O₅ attack in high temperature is excellent.