Microstructural evolution of (FeCoNi)85.84Al7.07Ti7.09 high-entropy alloy fabricated by an optimized selective laser melting process

Abstract

High-entropy alloy (HEA) FeCoNiAlTi (FCNAT) systems have been demonstrated to provide high strength while sustaining good ductility, which is of particular interest for the fabrication of structural components with complex geometries. Meanwhile, selective laser melting (SLM) technology that fabricated metallic material using layer-by-layer melting strategy can meet this demand. However, SLM fabrication technology has not yet been applied in conjunction with FCNAT-HEA systems, and the optimal SLM processing parameters and the microstructural characteristics of the resulting components remain unknown. The present study addresses this issue by fabricating highly dense (>99.9 %) cubic (FeCoNi)85.84Al7.09Ti7.07 FCNAT-HEA samples. The results demonstrate that the as-fabricated FCNAT-HEA samples possess highly non-equilibrium microstructures that form under the rapid heating and cooling cycles of the SLM process, and include typical overlapping between semi-elliptical melt pools, widely varying grain morphologies with coarse columnar grains and typical equiaxed grains with 〈001〉 growth orientation, dislocation network structures with elemental Ti and Al segregation, high-density L21-phase precipitates with sizes on the order of 200–300 nm, and near-spherical nano-sized Al-oxide particles. This research confirms the feasibility of fabricating FCNAT-HEA components by SLM, and therefore provides guidance for fabricating such HEA components with complex geometries.