Remarkable strength-ductility balance of boron-doped eutectic high-entropy alloys manufactured by laser powder-bed fusion after heat treatment

Eutectic high-entropy alloys (EHEAs) display superior mechanical properties, attributed to their lamellar structure characterized by alternating soft and hard phases. To address the critical demands for aerospace and high-end precision manufacturing equipment, a microalloying strategy has been employed to further achieve the balance of strength and ductility. Herein, we report that a unique AlCoCrFeNi_2.1 EHEA, doped with a trace amount of boron (300 ppm), manufactured by laser powder-bed fusion (LPBF), exhibiting a remarkable balance between strength and ductility after heat treatment. It achieves a yield strength of 1177 MPa, an ultimate tensile strength of 1517 MPa, and an elongation of 17.6 %. As compared with the undoped as-deposited samples, the boron-doped heat-treated alloys show a modest decrease in strength but a more than twofold increase in elongation. The doping of boron leads to a higher B2 phase content in the boron-doped as-deposited AlCoCrFeNi_2.1 samples, facilitating the formation of additional FCC precipitates during heat treatment and thus preserving the strength of the samples. Furthermore, a greater volume fraction of the FCC phase and lower residual stress positively impact the ductility of the samples. These results establish a theoretical foundation for the advancement of high-performance EHEA by additive manufacturing.