Alleviating mechanical-property anisotropy of additively manufactured dual-phase AlCoCrFeNi2.1 eutectic high entropy alloys by cyclic deep cryogenic treatment

• Deep cryogenic treatment (DCT) significantly enhances mechanical properties of dual-phase eutectic AlCoCrFeNi 2.1 produced by laser melting deposition. • DCT significantly reduces the anisotropy of mechanical properties arising from the eutectic microstructure of the as-printed AlCoCrFeNi 2.1 alloy. • The property and anisotropy improvements are shown, for the first time, to be due to microstructural evolutions arising from BCC to FCC phase transition under DCT. • For the first time, molecular dynamics (MD) simulation correctly predicts the phase separation of AlCoCrFeNi 2.1 into a eutectic microstructure. • MD simulation proves that the as-printed AlCoCrFeNi 2.1 alloy has a non-equilibrium phase ratio with FCC-phase depletion, thus confirming that BCC-to-FCC phase transformation is energetically favorable. Additive manufactured dual-phase eutectic high entropy alloys (EHEAs) have gained significant interest for the combined high strength of a BCC phase and high ductility of an FCC phase directionally arranged in a fine microstructure. However, the inherent anisotropy resulting from such a microstructure has been a limiting factor on application potential. In this research, cyclic deep cryogenic treatment (CDCT) is found to be an effective method to tune the microstructure and enhance the mechanical properties (increasing the yield stress by up to ∼34 %) and isotropy of laser melting deposited (LMD) dual-phase eutectic AlCoCrFeNi 2.1 high-entropy alloys. CDCT can induce higher tensile residual stress, phase transformation, grain rotation, redistribution of nano-precipitates and dislocation proliferation. Molecular dynamics (MD) simulations of structural stabilities indicate an energetically favorable transformation from BCC to FCC towards the thermodynamic equilibrium phase constitution. The elevated FCC ratio (from 50 % to 68 %) and lamellar rotation, driven by CDCT-induced increased residual stress levels, are identified as key factors in modifying crack propagation paths and failure modes, ultimately rendering the mechanical properties along the scanning direction (SD) comparable to those along the building direction (BD). Our findings highlight the effectiveness of CDCT in regulating heterogeneous microstructure to improve the anisotropic mechanical performance of additive manufactured alloys.