The effect of crystal orientation on fretting fatigue crack formation in Ni-based single-crystal superalloys: In-situ SEM observation and crystal plasticity finite element simulation

The effect of crystal orientation on fretting fatigue crack formation behaviors of Ni-based single crystal (NBSX) superalloys is investigated in this paper. Differences of slip lines and crack formation patterns between two crystal orientations are revealed by in-situ fretting fatigue experiments. The cracks are found to initiate along the direction of slip lines for both crystal orientations, which indicates the crack formation has close relations with crystallographic slip. Crystal plastic finite element method (CPFEM) simulation is implemented and shows the difference of slip system activations between two crystal orientations. Equivalent plastic strain is proved effective to predict crack formation sites and directions. The predicted slip lines and cracks obtained from CPFEM simulations are in good agreements with the experimental observations.