Microstructures and precipitation behaviors of a hypoeutectic high-entropy alloy prepared by laser powder bed fusion

Abstract

The trade-off between strength and ductility remains a significant challenge for high-entropy alloys (HEAs). The layer-by-layer printing manner inherent in the laser powder bed fusion (L-PBF) leads to distinctive microstructures in alloys, in turn yielding unexpected performances that are promising for resolving this contradiction. At present, the influence of L-PBF technology on the microstructures and mechanical properties of near-eutectic HEAs has yet to be explored. In the present work, a metastable AlCo0.4CrFeNi2.7 hypoeutectic HEA with an extraordinary strength-ductility combination was successfully fabricated using L-PBF. The precipitation behaviors and mechanical properties of the alloy were further modulated through annealing. The results reveal that the high cooling rates inherent in L-PBF promote the formation of a “pseudoeutectic” structure featuring the face-centered-cubic (FCC) + body-centered-cubic (BCC) dual-phase nanolamellae. Furthermore, after annealing at 600–750 °C, the L12 and B2 precipitates are generated in the FCC lamellae, accompanied by a coarsening of the original Cr-rich precipitates (BCC) in the BCC lamellae. The as-printed sample exhibits remarkable mechanical properties, posing a yield strength of 1007 MPa, an ultimate strength of 1249 MPa, and a total elongation of ∼25.1 %. After annealing at 750 °C, the tensile yield strength and ultimate strength are further increased to 1201 MPa and 1512 MPa, respectively, while the elongation is maintained at ∼15.1 %. The analysis results demonstrate that the high strength originates from the hard BCC lamellae and nanolamellar interfaces, while the good ductility stems from the soft FCC lamellae and coordinated deformation of the dual-phase nanolamellae. Furthermore, the strength increase is further substantiated through the introduction of annealing-induced nanoprecipitates, thereby contributing to additional precipitation strengthening.