Tailored microstructure and mechanical properties of AlCoCrFeNi2.1 eutectic high-entropy alloy fabricated by laser-directed energy deposition with different energy densities

In this study, AlCoCrFeNi 2.1 eutectic high-entropy alloy (EHEA) was fabricated by laser-directed energy deposition (L-DED) to investigate the effects of area energy densities (AEDs) on the relative densities, microstructures, and mechanical properties. Moreover, the phase transition mechanism and strengthening mechanism under different AEDs were revealed. The results show that the relative density first increases and then decreases with the increase of AED from 26.03 to 131.75 J/mm 2 . The optimal AEDs with a relative density ≥99.7 % are 43.48–69.57 J/mm 2 . The microstructure features a dual-phase (FCC + BCC) lamellar eutectic with epitaxial growth. The mutual diffusion of Al/Ni elements and Co/Cr/Fe elements at solid-liquid interfaces promotes the formation of BCC and FCC phases, respectively. With the increase of AED, the enhanced convective heat transfer and weakened conductive heat dissipation lead to a reduction in cooling rate (5.51 × 10 3 to 2.81 × 10 3 K/s), which result in the larger degree of phase transitions of L→ L + FCC→ FCC + BCC and thus cause a lower FCC phase content and higher BCC phase content. The maximum microhardness (358.1 HV 0.5 ) and ultimate tensile strength (1191.85 MPa) occur at AED = 60.87 J/mm 2 , while the maximum elongation (16.46 %) appears at AED = 52.17 J/mm 2 . The high yield strength primarily originates from the contribution of dual-phase nanoscale lamellar structures strengthening and dislocation strengthening. The match of tensile strength and ductility for AlCoCrFeNi 2.1 EHEA can be tailored by adjusting the energy densities.