Micro-strain and cyclic slip accumulation in a polycrystalline nickel-based superalloy

This work provides a comprehensive understanding of deformation and fatigue damage mechanisms in a nickel-based superalloy during ambient temperature fatigue and points to the fundamental deformation mechanisms that result in the onset of crack nucleation. Strain and slip irreversibility are investigated at the nanometer scale using high-resolution digital image correlation and high-resolution electron backscatter diffraction, highlighting distinct deformation mechanisms contributing to crack nucleation. It is observed during early fatigue cycling at relatively low applied stress, the formation of intense slip events that induce grain boundary shearing. It results in intense micro-strain in the neighboring grains, producing localized plasticity and stresses. Such stresses facilitate fatigue extrusion-intrusion mechanisms during subsequent cycling, resulting in early crack nucleation. Finally, the configurations within the microstructure that promote such deformation and damage mechanisms sequence are highlighted.