Degradation of microstructural and mechanical properties with serviced turbine blades

To study the degradation of directionally solidified turbine blades with different service times, four parts of four cross sections are selected to examine their microstructure through scanning electron microscopy. The width of the γ-phase channel, γ’ volume fraction, types of carbides, and elemental composition are chosen to characterize the damage. Creep tests are carried out at four heights on the upper and lower parts of the turbine blades, and the residual creep life is determined. The degrees of degradation of the blades are examined based on the microstructures and creep test results of the samples with respect to various service times. The results indicate that the quantitative description of the microstructure is consistent with the experimentally obtained results for the remaining creep life. The relationships between the residual lives of the small samples and the width of the γ-channel and γ'-phase volume fraction are presented in a three-dimensional graph. Based on the creep damage model, a method for predicting the remaining life of the turbine blades in service is established. The predicted results of the remaining life fit well with the model results.