Thin-wall effect on low-cycle fatigue behavior of a Ni-based single-crystal superalloy turbine blade material

The enhancement in thrust-to-weight ratio and thermal efficiency in aero-engines has led to the adoption of thin-walled turbine blades (<1 mm). Cooling is enhanced and thermal loads are reduced by this design, but fatigue performance is significantly degraded due to reduced wall thickness. The low-cycle fatigue behavior of cast Rene N6 single-crystal superalloy specimens with thicknesses of 0.6 mm and 0.8 mm is evaluated under stress-controlled loading (R = 0.1) at 760 °C, 980 °C, and 1070 °C. The influences of thickness on fatigue life, ratcheting strain, crack initiation, and crystallographic slip are analyzed. A pronounced reduction in fatigue life is exhibited by thinner specimens, with fatigue life reduced by over 50 % at 980 °C and up to approximately 58 % at 1070 °C. Crack initiation shifts from subsurface casting defects to surface oxidation-induced damage with increasing temperature. Crack propagation is observed along the {1 1 1} slip planes, and the inclination of fracture surfaces ranges from 30° to 60° depending on slip activity. Faster accumulation of ratcheting strain is induced by intensified local plastic deformation in thinner walls. An anisotropic fatigue-damage finite element framework is employed to interpret the thickness effect under stress-controlled low-cycle fatigue. The framework is informed by the {1 1 1}<1 1 0> slip systems through the Schmid tensor. It is also coupled with oxidation-induced section loss. This framework is used to analyze the influence of thickness in a physically consistent manner. The thickness effect is captured accurately, and fatigue life is predicted within 20 % error. The fatigue degradation mechanisms of thin-walled structures are clarified, offering a reliable tool for life prediction and design optimization.