Selective laser melted equiatomic CoCrFeMnNi high-entropy alloy: Microstructure, anisotropic mechanical response, and multiple strengthening mechanism

Abstract

One of the major challenges of equiatomic CoCrFeMnNi HEA is to manufacture parts with complex geometry that have higher yield strength. Equiatomic CoCrFeMnNi HEA was successfully fabricated in the present study with selective laser melting. The unique microstructure and mechanical anisotropy that generally appear in additive manufactured materials were investigated. SLM-built HEA has strongly oriented grains, dislocation networks, and nano-sized oxides. In addition, the average grain sizes were measured as 15.66 μm, 12.93 μm, and 5.98 μm on the plane perpendicular to the scanning direction (SD), transverse direction (TD), and building direction (BD), respectively. A compressive test measured outstanding yield strengths (YS) of 778.4 MPa, 766.4 MPa, and 703.5 MPa in the loading axis of SD, TD, and BD, respectively. These outstanding YSs are the result of a combination of fine grain sizes, high dislocation density and nano-sized oxides. In addition, anisotropy in mechanical properties are result from different values of Taylor factor and grain size according to the loading axis. After a compression test, the geometrically necessary dislocation density was found to differ about 2.5 times on each plane parallel to the loading axis in the same macro strain. Based on such findings, the relationship among microstructure, mechanical anisotropy and deformation mechanism are discussed in the present paper. Furthermore, the mechanical properties of SLM-built equiatomic CoCrFeMnNi HEA are predicted by using multiple strengthening mechanisms considering the microstructural characteristics.