Effects of Secondary Orientation and Recrystallization Grains on the Low‐Cycle Fatigue Behavior of DD6 Single Crystal Superalloy

ABSTRACT This study investigated the fatigue property of DD6 nickel‐based single crystal superalloy using in situ scanning electron microscopy (SEM), focusing on the coupled effects of secondary orientations ([010] and [110]) and recrystallization defects, representing the first comprehensive report of this synergistic interaction. Surface recrystallization significantly deteriorated fatigue resistance, with crack nucleation preferring recrystallized regions. [110]‐oriented specimens exhibited superior fatigue durability compared to [010]‐oriented counterparts in both pristine and recrystallized conditions. [010]‐oriented specimens showed pronounced cross‐slip activity, while [110]‐oriented samples maintained single‐slip deformation. Fatigue crack propagation in [010] orientation was governed by multi‐octahedral slip system activation. Combined electron backscatter diffraction (EBSD) analysis and crystal plasticity finite element modeling (CPFEM) demonstrated that [010]‐oriented specimens accumulated higher cumulative shear strain (CSS) under equivalent stress conditions compared to [110]‐oriented samples, directly correlating with reduced fatigue life. A unified fatigue life prediction model incorporating orientation and recrystallization effects was developed for cyclic loading evaluation.