Notch effect and its mechanism during creep rupture of nickel-base single crystal superalloys

In this research, the double notched plate mini-specimens have been designed to study the notch effect during creep. The experimental results show that the notch has strengthening effect. The scanning electron microscopy (SEM) photos of fractured surfaces reveal that void growth is the primary mechanism of creep rupture. Finite element analysis (FEA) with a modified form of Kachanov-Rabotnov damage law was carried out to simulate the damage evolution in the specimens. The creep damage calculations show that the creep is a process of stress redistribution. The 3-D voided unit cell model with the constant maximum principal stress was used to explore the mechanism of notch strength. The results show that the initial stress triaxility has remarkable influence on void growth. The greater the initial stress triaxility is, the slower the growth rate is. The stress state plays a main role in void deformation. The void grows remarkably in transverse direction when the stress triaxility is high. The void growth and coalescence is the main mechanism of creep rupture. The multiaxial stress state can inhibit the void growth, and this constraint effect is beneficial to the creep life.