THERMAL SHOCK RESISTANCE OF La2(Zr0.7Ce0.3)2O7 THERMAL BARRIER COATING PREPARED BY ATMOSPHERIC PLASMA SPRAYING

Abstract

Thermal barrier coatings(TBCs) are widely used in turbine engines to protect hot-section metallic components from corrosion and oxidation.The typical material of TBCs is 8YSZ due to its low thermal conductivity(2.1 W·m~(-1)·K~(-1)) and relatively high thermal expansion coefficient (1.1×10~(-5) K~(-1)).However,at temperature above 1200℃,it could hardly be used for long-term application for its low sintering resistance and low phase stability.So it is urgently needed to develop novel TBCs materials with higher phase stability and lower thermal conductivity than 8YSZ.Recently, some materials have been evaluated as the candidates for TBCs,such as LaMgAl_(11)O_(17)(LMA), La_2Zr_2O_7(LZ),La_2Ce_2O_7(LC) and La_2(Zr_(0.7)Ce_(0.3))_2O_7(LZ7C3).Among those interesting candidates, the LZ7C3 ceramic shows the promising thermophysical properties for high-temperature TBCs.In this paper,the novel thermal barrier LZ7C3 coating was prepared by atmospheric plasma spraying.The microstructure,phase structure,composition,phase stability,thermal conductivity and thermal shock behavior of LZ7C3 coating were studied.These results show that the coating had single pyrochlore structure with high phase stability in high temperature.The thermal conductivity of coating is 20% lower than the bulk material due to high porosity of coating.The thermal shock tests indicate that the lifetime and failure mechanism depend on the test temperature.The coatings are failed after 116 cyc thermal shock from 1000℃to room temrature.which is attributed to the spallation of lamella.The failure mode of lamella spallation and layer fracture are found when the coating tested at 1100℃, the thermal shock lifetime is 53 cyc.Whereas at 1200℃,the coatings are spalled entirely after 3 cyc thermal shock in the way of layer fractur at the interface between LZ7C3 and bond coat.