Influence of W on Solidification Microstructure and Mechanical Properties of AlCoCrFeNi2.1 Eutectic High-Entropy Alloy

Abstract

Alloying serves as an effective strategy for regulating the properties of eutectic high-entropy alloys. This study examines the impact mechanism of W alloying on the microstructure and mechanical properties of AlCoCrFeNi_2.1 eutectic high-entropy alloys (EHEAs). (AlCoCrFeNi_2.1)_(100−x)W_x (x = 0, 2, 4, 6, 8, 10) alloys were synthesized via vacuum arc melting under an argon atmosphere. Microstructure and properties were analyzed using XRD, SEM with BSE imaging and EDS and compression tests. Our research has found that adding W refines the lamellar spacing (W < 4 at.%), and higher concentrations (W > 4 at.%) induce a W-rich μ phase, thereby transforming the two-phase eutectic structure into a three-phase composite structure. This microstructural evolution enables the alloy’s compressive yield strength to increase from 541.6 to 661.4 MPa, while plastic strain initially rises and then drops. Among them, (AlCoCrFeNi_2.1)₉₈W₂ shows optimal strength-plasticity combination: 568.8 MPa yield strength, 2928.8 MPa fracture strength and 50.4% strain, which mechanical properties surpass those of most HEAs as well as traditional aluminum-, titanium-, iron- and nickel-based alloys, demonstrating its potential for application as a novel high-performance structural material. More importantly, this study proposes a simplified phase formation criterion based on valence electron concentration (VEC) and electronegativity difference (∆χ) to accurately predict the stability and coexistence relationships of FCC, BCC and TCP phases in multiphase high-entropy alloys. This criterion provides a critical theoretical foundation and design tool for rationally designing multiphase high-entropy alloys with customized microstructures and properties.