Synergetic strengthening of additively manufactured (CoCrFeMnNi)99C1 high-entropy alloy by heterogeneous anisotropic microstructure

Abstract

In this study, the heterogeneous anisotropic microstructure and mechanical properties of additively manufactured (CoCrFeMnNi)99C1 high-entropy alloy (HEA) are comprehensively investigated using experimental and theoretical analyses. For the present alloys, the selective laser melting (SLM) process produced orthogonally anisotropic microstructure with not only strong macroscopic morphological but also sharp microscopic crystallographic textures. Moreover, due to the complex thermal gradient and history in the melt pools, the columnar grains were heterogeneously evolved along the building direction with alternatively arranged layers of fine and coarse grains parallel to the laser scanning direction. This unique morphological texture played a dominant factor for the big difference in tensile properties between different loading directions in the early stage of deformation. In particular, the alternatively arrangement of fine and coarse grains could generate high hetero-deformation induced (HDI) hardening along the scanning direction in the as-built samples by profuse evolution of geometrically necessary dislocation at the boundaries of each layer. On the other hand, upon the last stage of plastic deformation, the crystallographic texture played a crucial role in directional flow behavior by modulating twinning activity. The combined contribution of the various anisotropic microstructural factors to the tensile properties of the SLM-processed HEAs was clarified both qualitatively and quantitatively. This work will shed light on effective utilization of both heterogeneity and anisotropy of the structural parts for customized performance via expanding multi-scale freedom of design in additive manufacturing.