Experimental Study And Theoretical Analysis Of Creep Behavior For Directionally Solidified Turbine Blade

The directionally solidified nickel-based alloy is widely used for the turbine blade of the advanced aeroengine recently. In order to enhance the reliability of design parameters and the design method for the turbine blade, tensile tests in short-term, low cycle fatigue tests and creep experiments have been performed on the model specimens cut from the typical part of the turbine blades.Tensile tests in short-term at room temperature,850℃and 980℃are carried out with MTS810 hydraulic servo material test machine. The stress-strain curves of the model specimens at corresponding temperature are received. Mechanical properties of the material are compared with those of standard specimens, and their differences are analyzed to direct the strength design for the turbine blade.Creep tests are grouped under different stresses at the same temperature (980℃). Creep deformation values of each specimen during the test are automatically collected at regularly given intervals, and the final fracture time is recorded. The experimental results show that 16 specimens'lives significantly decline in comparison with standard specimens'ones. The experimental lives of different specimens are discrete with each other even if in the same group at the same temperature and nominal stress. But for 4 groups of 5 groups, at least two specimens'lives are relatively close in each group.In order to validate the experimental data which vary distinctly from those of standard specimens, the finite element simulation is performed. Least square method is adopted in nonlinearly fitting the creep data at 980℃under 4 stresses to obtain parameters of Graham model. Moreover, a modification is proposed on the original Graham model in the ANSYS FEA (finite element analysis) software package. The modified model has been applied to simulate creep tests considering the orthogonal anisotropic property of material. The numerical simulation results are consistent with the experimental data, which proves the rationality of the modified model. The modified model is also used to extrapolate the creep data at 980℃under 200 megapascal and 250 megapascal, and results are desirable.Further, the modified Graham model is regarded as a forecasting model of the model specimen's creep rupture life at 980℃, and lives under different stresses are attained. The reliability of this model is verified by the comparison between the forecasted lives and experimental results.Low cycle fatigue tests are grouped under different stress amplitudes at the same temperature (980℃). All specimens'fracture cycles are too few and appear abnormally. Fracture and fine texture analyses show that test results are closely related to the defects in the microstructure of specimens.