In Situ Characterization And Finite Element Simulation Analysis Of Bending Properties Of (Gd_0.9Yb_0.1)₂Zr₂O₇ Coatings At Different Temperatures

Thermal barrier coatings?TBCs?with excellent thermal insulation properties and high temperature oxidation resistance have been widely applied in hot-end components of advanced aero engines.Many researchers are committed to developing new high-temperature coatings that meet more than 1200°C?such as rare earth doped zirconia and rare earth zirconates?at home and abroad.However,the high temperature failure of the coating is closely related to the evolution of its mechanical properties.Therefore,it is important to evaluate and characterize the high temperature mechanical properties of TBCs materials in service environments for improving coating material formulation,structural design and fabrication processes.At present,there is a lack of systematic analysis about the high temperature mechanical properties and the fracture failure mechanism of(Gd_0.9Yb_0.1)₂Zr₂O₇?GYbZ?.In this paper,the GYbZ coating was prepared by plasma spraying process.Then the nano-indentation technique was used to characterize the elastic modulus and hardness of the coating.Secondly,the mechanical properties of GYbZ coating were studied by three-point bending and single-edge notched beam method at different temperatures.Finally,the internal microstructure of GYbZ coating was obtained based on industrial CT technology,and the finite element mesh model with defects was established to study the effect on the mechanical properties.The main contents are summarized as follows,Firstly,the nano-indentation technique and three-point bending test were used to characterize the elastic modulus,hardness and fracture strength of the GYbZ coating.The results showed that the cross-section elastic modulus and hardness were larger than the surface.The flexural modulus of GYbZ coating was 4±0.19 GPa at T=25°C,increased to 9.5±2.9 GPa at T=1200°C,and then decreased to 3.0±0.92 GPa at T=1500°C.The fracture strength was 12±0.52 MPa at T=25°C,reached maximum at T=1200°C.The results showed that the flexural modulus and fracture strength of the coating increase first and then decrease with the increase of test temperature,then the failure strain continued to increase,reached 1.22±0.22%at T=1500°C.Secondly,the fracture toughness and strain energy release rate of GYbZ coating were characterized by single-edge notched beam and extended finite element method at different temperatures.The fracture toughness of the coating was 0.8±0.025MPa?m^1/2 at T=25°C,reached 1.9±0.17 MPa?m^1/2 at T=1400°C,and then decreased to 1.21±0.21 MPa?m^1/2 at T=1500°C.Meanwhile,the results showed that the strain energy release rate of GYbZ coating was 157 N/m at room temperature,reached 420N/m at T=1400°C,and then decreased to 345 N/m at T=1500°C.Thirdly,in order to study the effect of micro-defects on the mechanical properties of the coating,the internal microstructure of the GYbZ coating sample was scanned by industrial CT tomography.After the scanned image was subjected to image processing steps such as graying,binarization and segmentation,the microscopic defects in the GYbZ coating were extracted.The brittle cracking criterion was used to simulate the fracture failure of the GYbZ coating,and the cracking strain was 0.36±0.03%,which was in good agreement with the data obtained from the experimental results,thus the feasibility and reliability of the geometric reconstruction method were proven.