Microstructure and mechanical behavior of additively manufactured CoCrFeMnNi high-entropy alloys: Laser directed energy deposition versus powder bed fusion

CoCrFeMnNi high-entropy alloys (HEAs) are additively manufactured by laser directed energy deposition (L-DED) and laser powder bed fusion (L-PBF) processes. Comparative studies are conducted for the microstructures and deformation mechanisms of L-DED and L-PBF samples. In both types of samples, highly heterogeneous microstructures are formed, consisting of columnar grains, solidification cells, and dislocation networks. However, substantial differences are measured in the crystallographic texture, cell size, and elemental distribution. Deeper melt pools in the L-DED samples promote a mixed crystallographic texture of <101>/<111> as opposed to <001> along the build direction in the L-PBF samples. The <101>/<111> texture elevates the flow stresses and facilitates the activation of deformation twins in the L-DED samples. Moreover, their larger solidification cell sizes and associated chemical segregation across cell walls increase the dislocation storage capability and resistance to dislocation motion, leading to profuse planar slip bands and microbands during plastic deformation. The enhanced plastic deformation capabilities in the L-DED samples give rise to more sustained strain hardening and thus higher ductility compared to the L-PBF samples. Our work not only provides fundamental insights into the deformation mechanisms of additively manufactured HEAs, but also underscores the critical impact of processing conditions on the solidification microstructure and material design by additive manufacturing.