Abstract: Additive manufacturing, commonly known as 3D-printing, of high-entropy alloys (HEAs) has garnered significant attention for its ability to create intricate geometries and tailored microstructures. HEAs exhibit superior mechanical properties, including high strength, ductility, and resistance to wear, corrosion, and high temperatures, making them well-suited for use in demanding environments. However, the successful application of 3D-printed HEAs depends critically on understanding their deformation mechanisms under dynamic fatigue loading. This study delves into the microstructural features and deformation mechanisms of a CrMnFeCoNi HEA fabricated via laser-beam powder bed fusion, subjected to cyclic loading at a strain ratio of R =-1. Detailed electron backscatter diffraction (EBSD) analysis of microstructurally small cracks revealed significant grain rotation driven by the activation of multiple slip systems, with misorientations up to 30° in the reoriented regions, which rotated mainly from the 〈001〉 pole towards the 〈101〉 pole. Notably, curvilinear deformation twinning was identified ahead of the crack tip, while higher-lower strain boundaries within the elongated grains provided low-energy transgranular paths for crack propagation. Additionally, the localized plastic deformation on one side of the crack caused uneven displacement of crack surfaces, enhancing roughness-induced crack closure. The findings shed light on the deformation mechanisms of HEAs, paving the way for expanding their applications in cyclic load-bearing structures.

Key words: Electron backscatter diffraction (EBSD), Grain rotation, Crack propagation, Cyclic micro-plasticity, Deformation twinning