High‐Cycle Fatigue Behavior and Deformation Mechanisms of Al _0.5 CoCrFeNi High‐Entropy Alloy by Laser Powder Bed Fusion

ABSTRACT Laser powder bed fusion (LPBF) can fabricate high‐entropy alloys (HEAs) with refined microstructure and enhanced mechanical properties. However, the deformation and fatigue mechanisms of Al‐containing HEAs produced by LPBF remain unclear. In this work, we systematically investigate the tensile properties, deformation mechanisms, and high‐cycle fatigue (HCF) response of Al 0.5 CoCrFeNi HEA fabricated by LPBF. The results show that the as‐printed HEA exhibits a remarkable synergy of high strength and ductility at room temperature (899 MPa and 39%). Monotonic deformation is mainly dominated by planar slip, microband formation, and the development of lamellar dislocation boundaries, whereas deformation twins are absent even near fracture. Under cyclic loading, the HEA shows a pronounced stress sensitivity, and fatigue life decreases sharply at 450 MPa (43,802 cycles) but increases to 544,320 cycles at 400 MPa. When the stress amplitude is 340 MPa, the number of cycles exceeds 10,000,000 without specimen failure. Interestingly, deformation twinning was observed during cyclic loading, particularly near the crack tip. The high lattice friction stress inherent to the alloy effectively suppresses widespread cyclic strain localization, contributing to its improved fatigue resistance at moderate stress. This study provides a comprehensive understanding of the deformation and fatigue mechanisms of LPBF HEAs and offers guidance for designing high‐strength fatigue‐resistant additively manufactured HEAs through lattice‐friction engineering.