Crystal plasticity finite-element modelling of cyclic deformation and crack initiation in a nickel-based single-crystal superalloy under low-cycle fatigue

Nickel-based single-crystal superalloys are predominantly used for turbine blades in aircraft engines and land-based gas turbines. Understanding and predicting the fatigue failure of Ni-based single-crystal superalloys are critical to ensure the safety of these components during operation. In this paper, low-cycle fatigue experiments were carried out to investigate cyclic deformation of a nickel-based single-crystal superalloy MD2, recently developed by GE Power, with different crystallographic orientations. Specialty in situ scanning electron microscope (SEM) tests were also conducted to study the slip-controlled initiation of short cracks under low-cycle fatigue. In particular, the stress-strain response for both [001] and [111] orientations was used to calibrate a crystal plasticity model, which allowed us to simulate the activation of crystallographic slip systems and predict the initiation of short fatigue crack. Using the accumulated shear strain as a criterion, the simulations confirmed that the slip system with the maximum accumulated shear strain appeared to control the crack initiation. The location and direction of slip traces and short cracks, captured by the crystal plasticity finite-element simulations, agreed with the in situ SEM observations. The modelling tool will be valuable for assessing the structural integrity of critical gas turbine blades.