Microstructure, Tribological Properties, and Corrosion Resistance of Multiphase AlCoCrFeNb _0.4 Ni _2.1 High‐Entropy Alloy: The Role of Heat Treatment Time at 800 °C

This study fabricates AlCoCrFeNb 0.4 Ni 2.1 high‐entropy alloy (HEA) via vacuum induction melting and systematically investigates how heat treatment duration (0–18 h at 800 °C) regulates its microstructure, tribological performance, and corrosion resistance. The as‐cast HEA features a face‐centered cubic + body‐centered cubic (FCC + BCC) eutectic structure and (Co–Cr–Fe) 2 Nb‐type Laves phase, with FCC precipitates already existing in the BCC phase. Heat treatment triggers dual precipitation behavior: FCC phases further precipitate in BCC matrices, and Laves phases form in FCC phases, with both precipitate fraction and size increasing with prolonged holding time. This microstructural evolution expands grain boundary spacing, reducing hardness and wear resistance, yet the wear mechanism (synergistic oxidation, adhesion, and abrasive wear) remains unchanged. Strikingly, heat treatment enhances corrosion resistance by promoting passive film formation/repassivation via Nb‐rich Laves phases, with the 18 h‐treated HEA achieving optimal corrosion performance. Notably, the 2 h‐treated HEA retains favorable hardness and wear resistance while lowering the friction coefficient, providing a novel strategy for tailoring HEAs with balanced mechanical and tribological properties.