1.State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China
2.Xi’an Aerospace Engine Corporation in CASC, Xi’an 710065, China
3.The Second Military Representative Office of the Rocket Force Equipment Department in Xi’an, Xi’an 710065, China
Gd2Zr2O7(GZO) has a stable phase structure until its melting point and has low thermal conductivity. It is one of the most potential materials to replace yttria-stabilized zirconia（YSZ） as the ceramic layer of thermal barrier coatings(TBCs). However, the low fracture toughness restricts the engineering application of GZO. In order to achieve long life span GZO-TBCs, this study prepared YSZ+GZO double layer TBCs and investigated the influence of sintering-induced hardening on failure mechanism. The results show that the thermal cycle life of YSZ+GZO double layer TBCs is 12 times higher than that of GZO single layer TBCs. GZO coating has no phase transformation after thermal cycle. After 100 hours of heat exposure at 1250 ℃ and 1450 ℃, its apparent porosity decreased by 46.0% and 59.8% respectively, and its hardness increased by 79.0% and 1238%, which changed rapidly in the early stage of heat exposure and gradually slowed down in the later stage. By observing the healing behavior of longitudinal cracks in the layer, unbound areas between layers and spherical pores in high temperature heat exposure, it is found that the micro defects of the coating gradually heal, resulting in the increase of density and gradual hardening of the coating, which is one of the main reasons for the failure of the coating.