An evaluation of the fatigue crack propagation rate for powder metallurgical nickel-based superalloys using the DCPD method at elevated temperatures

This study investigates the fatigue-crack propagation behavior of a powder metallurgical nickel-based superalloy, used in aircraft turbine disks. Taking into consideration the various operating conditions, the fatigue-crack propagation tests were conducted at various temperatures and stress ratios. These tests were performed with using the direct current potential drop method suggested by ASTM E647. Using Paris' law, the fatigue life can be predicted and the fatigue strengths can be calculated for developing a damage-tolerant design to predict the defects at elevated temperatures. The fatigue crack propagation rates at elevated temperatures are higher than that at room temperature. In addition, scanning electron microscope (SEM) observations of the fracture surface at different temperatures were examined and compared. At elevated temperatures, intergranular fractures are appeared with the oxidation.