Fatigue Fracture Behavior and Residual Life Prediction of DD6 Superalloy With Precrack Damage

The crack propagation paths of DD6 superalloy samples with precrack damage were obtained by vibration fatigue test. By analyzing the dislocation behavior at the crack source region, the microscopic behavior and mechanism of vibration fatigue crack propagation were explored, and a residual life evaluation model for the alloy with precrack damage was established. The results show that the fatigue cracks of both undamaged and precracked samples propagated along the 111 crystal planes in the form of straight line. For vibration fatigue test at 850 ℃/340 MPa, the residual life model of DD6 superalloy is ln N=-1.16ln a+11.24, R=0.92, with good prediction effect. The cracks of the samples with pre-crack damage initiated from the notch, and the sources are mainly located at the intersection of the notch and the plate thickness, and the crack tip inside the notch also has sources. The dislocation density at the source region of the samples with longer fatigue life is relatively lower, while the stress concentration at the source region of the samples with shorter fatigue life increases, thereby reducing the resistance to dislocation slip in the matrix.