Effect of multi-component rare-earth doping on maintaining structure stability of RE2Zr2O7 (RE = La, Sm, Gd, Y, Yb) coatings under thermal cycling

Inspired by the high entropy effects of high-entropy components, a novel high-entropy rare-earth zirconate (La1/5Gd1/5Y1/5Sm1/5Yb1/5)2Zr2O7 (HEC-LZ) was designed and successfully synthesized in this work. In addition, two binary rare-earth doped zirconates (RE-LZ), (La1/3Sm1/3Yb1/3)2Zr2O7 (LSYZ) and (La1/3Gd1/3Y1/3)2Zr2O7 (LGYZ), were proposed using the same rare-earth elements for comparison. The thermal barrier coatings with LZ-based ceramic top layer were prepared by spray granulation, solid-phase synthesis and atmospheric plasma spraying techniques. The as-synthesized LZ-based ceramics are all dominated by the pyrochlore phase. Under 1000 °C, the thermal cycling performances of the three coatings were studied. The microstructure evolution and crack expansion during the failure process were investigated in detail. The strengthening mechanism and the cause of coating spallation are proposed in combination with mechanical properties and thermal matching analysis. The results showed that compared with the undoped LZ coating, the thermal shock life of LGYZ coating, LSYZ coating and HEC-LZ coating is improved by nearly 46%, 27% and 57%, respectively. Due to the characteristics of high randomness, HEC-LZ ceramic has a large lattice distortion than RE-LZ ceramics, resulting in a higher coefficient of thermal expansion and fracture toughness, which contributes to maintaining the structure stability of coatings under thermal stress.