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Fatigue crack growth damage mechanisms for nickel-based superalloys at high, negative stress ratios challenge classical crack tip shielding and closure concepts. Fatigue crack growth rate and crack closure for single-edge notch Ni-based superalloy 718 specimens at 100 °C were evaluated for several stress ratios (0.5, 0.1, −1, and −2). Multiple methods were used to calculate the effective driving force for crack growth rates in region II (i.e., Paris or power law regime). The relationships between the effective driving forces, the experimentally-measured crack closure levels, and the fractographic evidence of damage mechanisms are discussed. • A negative opening load was observed at the highest negative stress ratios (−2). • The opening load decreased with increasing crack growth rate at stress ratios < 0. • Secondary cracking and deformation bands on fracture surfaces at stress ratio of −2. • Bauschinger-sensitivity contributes to fatigue damage at high negative stress ratios. [ABSTRACT FROM AUTHOR]