Enabling stronger eutectic high-entropy alloys with larger ductility by 3D printed directional lamellae

Eutectic high-entropy alloys (EHEAs) that consist of at least two phases with different properties are promising candidates for engineering applications. However, the reported EHEAs still have difficulty competing with traditional alloys because the as-cast alloys are either not strong enough or brittle, while high-strength and ductile EHEAs produced by severe plastic deformation (SPD) are not suitable for preparing industrial-grade products. This work demonstrates a strategy for simultaneously improving the strength and ductility of EHEAs by introducing directional eutectic cells with ultrafine two-phase lamellae, whose formation is different from single-phase solidified alloys like superalloys and depends strongly on 3D printing process control. Compared with the as-cast samples, a strength increment of ~60% (close to 300 MPa) is achieved without a loss in ductility when tensile loading is applied in parallel to these 3D-printed directional lamellae. Furthermore, owing to the technical advantage of layer-by-layer additive manufacturing, these excellent mechanical properties, which are comparable to those of the SPD samples, can be obtained in large engineering parts. These results are important for understanding two-phase directional cellular solidification behavior in 3D-printed parts, and can offer more possibilities for performance improvement by microstructural design using 3D printing.