The influence of temperature and orientation on fatigue crack growth behavior of a directional solidification nickel-based superalloy: Experimental investigation and modelling

The fatigue crack growth (FCG) behaviour of a directional solidification nickel-based superalloy DZ125 samples (L- and T-orientated directions) were conducted at 750, 850 and 925 °C. Results showed that the FCG rate at elevated temperature increased significantly compared with that at room temperature. However, the reduced difference between room and elevated temperature can be observed in later stage due to oxidation induced closure effect. In addition, the influence of orientation is limited at elevated temperature while this is more evident at room temperature. To further reveal the process of crack propagation, the fractography was also examined by SEM and EDS method, and oxidation features were found at elevated temperature. Finally a modified phenomenological parameter was proposed to make test data of different orientation and temperature fall into a narrow [1/2, 2] band, which shows less temperature dependence compared with crack tip driving force parameter ΔK under the linear elastic fracture framework.