Low-cycle fatigue behavior of WAAM TC4 dual-phase titanium alloys: Experiments and microstructure-based crystal plasticity modeling

During Wire arc additive manufacturing (WAAM) deposition, excessive heat buildup promotes microstructural heterogeneity and compromises fatigue resistance. To clarify the effect of thermal history, three heat treatment schedules were designed to study microstructural evolution and its impact on the mechanical behavior of WAAM TC4 dual-phase titanium alloys, with emphasis on low-cycle fatigue (LCF). By tailoring α lamellae morphology and combining tensile, nanoindentation, and LCF tests, mechanical responses under different grain orientations and temperatures were examined. Results show that higher HT temperature and holding time cause α lamellae coarsening, lower strength and fatigue life, but increased ductility, hysteresis loop area, and cyclic softening. High-temperature fatigue further revealed a fracture transition from tear ridges to dimples, wider striations, and faster crack growth. Meanwhile, a microstructural modeling framework integrating Computer Vision was established and incorporated into crystal plasticity finite element simulations to investigate the role of α morphology in fatigue. Validation against EBSD analyses confirmed the reliability of the RVE models and highlighted the dominant factors affecting LCF: α / β phase boundaries and low-angle grain boundaries act as primary sites for stress concentration and plastic strain accumulation, while grain orientation differences cause hard grains to carry higher local stresses, serving as preferential crack initiation sites. Finally, a damage evolution model based on accumulative plastic strain predicted LCF lives under different strain amplitudes, HT conditions, and temperatures, demonstrating accuracy and applicability. These findings clarify the microstructure–fatigue relationship of WAAM TC4 alloys and guide fatigue optimization and service life prediction of additively manufactured components.