Introduction Thermal barrier coatings can be used for the stable operation of aircraft engines under high-temperature environments due to their excellent oxidation resistance, corrosion resistance and heat insulation properties. However, the high-temperature phase transition of conventional 8.0% (in mass fraction) Y2O3 stabilized ZrO2 ceramic (8YSZ) materials exists when the service temperature exceeds 1 200 ℃. Developing thermal barrier coatings, such as rare-earth zirconates and rare-earth silicate, becomes popular. (Gd0.9Yb0.1)2Zr2O7 (GYbZ)/8YSZ coatings with a low thermal conductivity and a high temperature phase stabilization are regarded as potential thermal protective materials. At present, some work focus on the preparation properties optimization of air plasma spraying, electron beam physical vapor deposition and plasma spray physical vapor deposition techniques, respectively. It is important to in-situ investigate the mechanical properties and failure mechanisms of GYbZ/8YSZ coatings at > 1 200 ℃.Methods GYbZ/8YSZ thermal barrier coatings were prepared with NiCrAlY, 8YSZ and GYbZ powders on an Inconel 600 nickel-based superalloy with the thickness of 2 mm via air plasma spraying. GYbZ/8YSZ thermal barrier coatings were subjected to thermal cycle treatments in a Muffle furnace at 1 100 ℃ for 1 h, and then cooled to room temperature for 1 thermal cycle. The times of thermal cycles were 10, 50 and 100, respectively. The phase and microstructure of the coatings were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) before and after heat-treatments. The elastic modulus, hardness, fracture toughness and residual stress were measured by an indentation method at different temperatures.Results and discussion The XRD patterns show that GYbZ powder and the as-sprayed coating are a defective fluorite structure, and the doping of Yb3+ with small ionic radius makes the material change from a pyrochrite structure to a defective fluorite structure. In addition, the samples treated for different thermal cycles all maintain a defective fluorite structure, indicating that GYbZ has an excellent high-temperature phase stability. The SEM images show that the surface of the as-sprayed GYbZ coating has a good melting state，and massive micro-cracks are distributed on the surface, which is caused due to the quenching stress generated by the molten spray particles during the preparation process and the thermal stress generated by the mismatch between the thermal expansion coefficients between the layers. The bonding between the layers of GYbZ/8YSZ coatings is good, and the bonding interface is clear without any cracks. There are tiny pores in the interior. The distribution of elements in each layer is consistent with the design. After thermal cycling, the crack width of the coating surface gradually widens and the porosity gradually decreases. The thermal growth oxide (TGO) produced between the bond layer and the 8YSZ layer gradually increases, and the TGO grows to 20 μm after 100 thermal cycles. The generation of TGO leads to a large amount of stress concentration, leading to the initiation and rapid expansion of transverse cracks in the bonding layer and 8YSZ, and damages the structural stability of the GYbZ/8YSZ coatings. Also, some vertical cracks occur in GYbZ layer and 8YSZ layer. The results of element distribution test show that the oxygen content in the bond layer increases gradually with the increase of the number of thermal cycles. The creation of vertical cracks in the coating promotes the diffusion of oxygen, thus accelerating the growth of heat-grown oxides.The results of mechanical properties test show that the elastic modulus and hardness of GYbZ/8YSZ coatings surface firstly increase and then decrease with the increase of thermal cycle, and have the maximum values at 50 thermal cycles. After thermal cycling, the coating is sintered and its densification is improved, resulting in an increase in the elastic modulus and hardness. After 100 thermal cycles, the coating oxidation is serious, the binding force between coatings is weakened, massive vertical cracks occur in the coating, the coating structure is damaged, the deformation resistance is weakened, and the elastic modulus and hardness are reduced. The hardness of the coating decreases from 5.09 GPa to 2.20 GPa from room temperature to 700 ℃. At 700-1 100 ℃, the hardness of the coating is 2.00 GPa. The residual stress of the as-sprayed coating is -41.02 MPa. The residual stress accumulates due to thermal expansion mismatch of coating system during thermal cycling. After 10 thermal cycles, the residual stress accumulates to -147.30 MPa. After 50 thermal cycles, the stress relaxation caused by cracks gradually reduces the residual stress. After 100 thermal cycles, the residual stress decreases to -105.92 MPa. The results show that the residual stress of the coating before and after thermal cycling is a compressive stress. The fracture toughness of the as-sprayed GYbZ coating is 0.93 MPa·m1/2. The fracture toughness of the coating firstly increases and then decreases with the increase of the number of thermal cycles, and has a maximum value of 2.02 MPa·m1/2 after 50 thermal cycles. After heat-treatment, the pores of the coating reduce, and the dense area and the compressive stress can prevent the crack propagation. Some microcracks can increase the strain tolerance of the coating to a certain extent, and enhance the fracture toughness of the coating. After 100 thermal cycles, oxidation and massive destructive cracks lead to the instability of the coating structure, the increase of defects and the decline of performance.Conclusions The pore distribution in the as-sprayed GYbZ/8YSZ coatings was uniform, and the bonding interface of each layer was clear. Before and after thermal cycling, GYbZ coating was a defective fluorite structure and had an excellent high-temperature stability. The density of the coating increased with the increase of the number of thermal cycle, occurring some transverse and vertical cracks, and the TGO thickness grew to 20 μm. After 50 thermal cycles, the elastic modulus and hardness reached the maximum values, which were 182.01 GPa and 9.13 GPa, respectively. From room temperature to 700 ℃, the coating hardness reduced to 2.20 GPa. At 700-1 100 ℃, the coating hardness was 2.00 GPa. During the thermal cycle, the residual stress of the coating varied from -41.02 MPa to -123.67 MPa, and the fracture toughness varied from 0.93 MPa·m1/2 to 2.02 MPa·m1/2.