AN INVESTIGATION ON HOT CORROSION RESISTANCE OF PLASMA SPRAYED COMPOSITE YSZ-GD_2ZR_2O_7 AND GD_2ZR_2O_7 THERMAL BARRIER COATINGS IN SIMULATED TURBINE ENVIRONMENT AT 1050°C

摘要

Thermal barrier coatings (TBCs) are frequently used on hot section components in gas turbines. Rare-earth zirconate ceramics used as thermal barrier coatings have attracted increasing interest in recent years due to their distinctly lower thermal conductivity than common TBC material; Yttria stabilized zirconia (YSZ). This paper investigates the hot corrosion resistance of composite YSZ+Gd_2Zr_2O_2 and Gd_2Zr_2O_2 coating, in Na_2SO_4+V_2O_5 at 1050°C. Chemical interaction is found to be the major corrosive mechanism for the deterioration of these coatings. Characterizations using X-ray diffraction (XRD) and scanning electron microscope (SEM) indicate that the reaction between NaVO_3 and Y_2O_3 in YSZ produces YVO_4 and leads to the transformation of tetragonal ZrO_2 to monoclinic ZrO_2. Then For the Gd_2Zr_2O_7+YSZ composite coating, by the formation of GdVO_4, the amount of YVO_4 formed on the YSZ+Gd_2Zr_2O_7 composite coating is significantly reduced, thus the amount of monoclinic phase in the TBC coating is substantially reduced. Comparing to YSZ, under a high temperature of 1050°C, Gd_2Zr_2O_7 is more stable, both thermally and chemically, So Gd_2Zr_2O_7 exhibits a better hot corrosion resistance than YSZ+Gd_2Zr_2O_7 composite coating.