Aging‐Induced Microstructural Evolution and Impact on the Corrosion Behavior of a High Strength‐Ductility L1 ₂ ‐Type CoCrNi High‐Entropy Alloy in Sulfuric Acid

Aging‐induced microstructural evolution and its influence on corrosion behavior were investigated in a Co 35 Cr 20 Ni 35 Al 5 Ti 5 high‐entropy alloys. Aging at 800°C for 4 h promoted the formation of nanoscale coherent L1 2 precipitates within the face‐centered cubic (FCC) matrix, significantly improving yield strength from 813.71 to 1257.65 MPa and ultimate tensile strength from 1279.00 to 1720.74 MPa. Electrochemical tests in 0.5 M H 2 SO 4 revealed that aging shifted the corrosion potential negatively and increased passive current density, implying inferior corrosion resistance. Electrochemical impedance spectroscopy (EIS) and X‐ray photoelectron spectroscopy (XPS) analyses confirmed reduced passive film resistance and Cr 2 O 3 fraction, together with increased hydroxides, indicating a less compact oxide film. The degradation arises from galvanic coupling between L1 2 precipitates and the FCC matrix and the reduced Σ3 grain boundary fraction. This study reveals that aging enhances mechanical strength but compromises corrosion resistance in L1 2 ‐type CoCrNi HEAs, emphasizing the need to balance precipitation strengthening and electrochemical stability.