New insight into tailorable eutectic high entropy alloys with remarkable strength-ductility synergy and ample shaping freedom fabricated using laser powder bed fusion

摘要

Eutectic high entropy alloys (EHEAs) are typical heterostructured materials comprising ductile and hard phases that can be easily tailored to fabricate components with desirable structures and properties. Herein, an AlCoCrFeNi_(2.1) EHEA with dual-phase nanolamellar structure and high strength and ductility (yield strength (σ_(YS)) = 1210 MPa, ultimate tensile strength (σ_(UTS)) = 1414 MPa, and elongation (ε) = 16%) was produced using laser powder bed fusion (LPBF). The AlCoCrFeNi_(2.1) EHEA presented fine-grain structure with nanoprecipitates (L1_2 and BCC phases) embedded within alternating FCC and B2 nano-scale lamellae. We demonstrated that the high strength of the EHEA originated primarily from the high back stress strengthening of fine grains and high-density heterophase interfaces, and high dislocation density caused by rapid solidification as well as dispersed nanoparticles provided extra strengthening. Furthermore, the cellular structure comprising nearly square FCC cells and surrounding B2 phases was observed, which was induced by the presence of oxides on the surface of the feedstock powder. AlCoCrFeNi_(2.1) EHEA with two-hierarchical dual-phase structure, that is, a mixture of lamellar and cellular structures, was obtained. Such heterogeneous structure presented outstanding strength-ductility synergy (σ_(YS) = 1042 MPa, σ_(UTS) = 1303 MPa, and ε = 26%). These results promote the development of high-performance materials with manufacturing flexibility using additive manufacturing approaches to tailor their multiscale microstructure.