Effect of Si Doping on the Microstructure and Mechanical Properties of Alcocrfeni2.1six High-Entropy Alloys

Abstract

Eutectic high-entropy alloys (EHEAs) exhibit excellent properties including high strength, good processability, and thermal stability, offering promising application prospects. The goal of high-performance materials is to achieve great strength and ductility. In this work, the designed AlCoCrFeNi2.1Six (x = 0, 0.05, 0.1, 0.15, and 0.2) EHEAs are expected to demonstrate increased strength-ductility by optimizing the Si content to control the microstructure and phase proportion. The effect of doped Si on the modification of the microstructure and mechanical characteristics of EHEAs was explored, and the strengthening mechanism of doped Si on the high strength-ductility was revealed. AlCoCrFeNi2.1Six maintains the FCC and B2 (BCC) dual-phase structures. The microstructure changed from a typical lamellar to a petal-like form as the Si content increased. The volume fraction of the B2 phase increased from 22% to 49%, the average grain size of the FCC/B2 phases and nanoprecipitates within the B2 phase increased significantly, and the hardening ability of AlCoCrFeNi2.1Six increased. Compared with AlCoCrFeNi2.1, AlCoCrFeNi2.1Six exhibited a synergistic improvement in strength and ductility. AlCoCrFeNi2.1Si0.15 represents the best mechanical properties, with a 45% increase in ultimate tensile strength (UTS) and total elongation (TE). This improvement is attributed to the effective regulation of the FCC/B2 (BCC) microstructure to achieve the synergistic effects of solution strengthening, dislocation strengthening, and nanoprecipitate strengthening.

Keywords: Eutectic high-entropy alloys, Microstructure, Nanoprecipitates, Synergistic enhancement, Strength and plasticity