Laser directed energy deposited eutectic high entropy alloy with tailored lamella structure via interlayer pause strategy

Abstract

Eutectic high entropy alloys (EHEAs) have garnered significant attention due to their unique heterogeneous lamella structure, which imparts a desirable strength-ductility combination. Additive manufacturing (AM) techniques further exploit the advantageous properties of EHEAs through efficient fabrication and rapid heating/cooling processes. In this study, we fabricate near-fully dense and crack-free AlCoCrFeNi_2.1 EHEA samples with an alternating nano-scale eutectic lamellar structure composed of disordered face-centered cubic (FCC) and ordered B2 phases using the laser directed energy deposition (LDED) method. By using a novel and simple interlayer pause strategy, we have found that the eutectic lamellar structure can be significantly refined, achieving approximately 40% greater refinement compared to the case without interlayer pause. The optimized EHEA exhibits an exceptionally high strength of 1214 MPa and a sufficient uniform elongation of 16.3%, outperforming the non-interlayer-pause counterpart by 14% in strength and 47% in uniform elongation. The superior mechanical properties of the AlCoCrFeNi_2.1 EHEA are attributed to the synergistic effects of heterogeneous deformation-induced (HDI) strengthening and strain hardening mechanisms. Furthermore, the refined eutectic lamellar structure can effectively mitigate stress concentration mediated the formation of microcracks, thereby delaying fracture and maintaining plasticity. The interlayer pause strategy presented in this work offers a simple yet effective approach and valuable insights for the preparation of metallic materials with exceptional mechanical properties via LDED process.