Microstructures and properties of an equimolar AlCoCrFeNi high entropy alloy printed by selective laser melting

Abstract The equimolar AlCoCrFeNi high entropy alloy (HEA) was printed by selective laser melting (SLM), with emphasis on its densification, phase identification, non-equilibrium microstructure and properties. The density of SLM samples increase gradually with the increase of volumetric energy density (VED) with the maximal relative density 98.4%. SLM samples are consisted of disordered body-center cubic phases (A2) and ordered body-center cubic phases (B2) which are different from the conventional cast or deformation with A2 and fcc phase; the content of B2 phase increases with the VED. Interestingly, the Fe-Cr precipitate, which has never been found in the cast one, is observed in the SLM one without heat treatment. The microstructure of SLM samples shows epitaxial growth of columnar A2 grain bundles perpendicular to the melt pool boundary with an average grain size of about 1.5 μm; the B2 phase is between the columnar A2 grains. At low VED, the SLM sample shows preferred orientation, and is gradually transformed to the crystallographic direction families at a higher VED. Besides, there exists the {100} A2 ∥{100} B2 orientation relationship in A2 and B2 phase. The maximal micro-hardness of 632.8Hv of SLM sample is higher than the cast one and the electron beam melting printed one.