Enhancing mechanical properties of hypoeutectic high-entropy alloys via composition engineering and laser powder bed fusion technique

Abstract

Despite the growing interest in dual-phase high-entropy alloys (HEAs) for their unique combination of strength and ductility, some hypoeutectic HEAs still exhibit inadequate mechanical properties under tension. This study proposes a novel design strategy to enhance the mechanical performance of a specific hypoeutectic HEA (Al_16.596Cr_12.048Co_15.060Fe_15.060Ni_37.650V_3.012Si_0.461C_0.065B_0.048). This approach leverages local inhomogeneity in powder mixing and the benefits of gradual printing and rapid solidification in additive manufacturing (AM). Unlike the traditional method of simply mixing pure elemental powders, the hypoeutectic HEA composition is divided into two components: one containing Al and having a face-centered cubic (FCC) structure, and the other being an Al-rich alloy. These pre-alloyed powders are mixed and remelted using the laser powder bed fusion (LPBF) technique to fabricate bulk samples, which leads to a heterogeneous distribution of phase types and grain sizes. The LPBF-fabricated HEA samples do not exhibit the typical hypoeutectic microstructure but instead display a dual-phase structure. Specifically, the refined FCC grains contain fine B2 phases, while the refined body-centered cubic (BCC) grains incorporate small FCC crystals. These microstructural transitions significantly enhance the mechanical properties of the samples. The Vickers hardness increases to 458 ± 5 HV, the yield strength reaches 1028 ± 10 MPa, and the ultimate tensile strength attains 1377 ± 10 MPa while maintaining comparable elongation. These improvements are primarily attributed to the refined grain structure and the presence of fine B2 phases within the FCC grains, as well as small FCC crystals within the BCC grains. The complex heterogeneous microstructure also induces significant back stress, which ensures stable strain-hardening rates during deformation. This study demonstrates a promising approach to improving the mechanical properties of hypoeutectic HEAs through compositional engineering and AM techniques.