Precipitate evolution, recrystallization, and mechanical properties of an ultrastrong high-entropy alloy strengthened by L1₂ discontinuous precipitates

Abstract

Discontinuous precipitation (DP) has emerged as an effective strategy for designing high-entropy alloys (HEAs) that combine high strength and excellent ductility, highlighting the importance of understanding how microstructural changes influence mechanical properties. In this study, we systematically investigated the precipitate evolution, recrystallization, and mechanical properties of a DP strengthened (CoCr₀.₅FeNi₁.₅)₈₇.₅Al₇.₅Ti₅ alloy under various aging conditions between 500 and 800 °C. As the aging temperature increases, both recrystallization and DP kinetics are significantly accelerated, resulting in the rapid formation of nanorod precipitates and the development of fully recrystallized ultrafine-grained structures. Kinetics analyses indicate that DP structures exhibit a low activation energy for coarsening (106 kJ/mol), attributable to the synergistic effects of rapid diffusion along grain boundaries and substantial interfacial energy. The DP strengthened alloy also demonstrates a low activation energy for recrystallization (240 kJ/mol), which arises not only from conventional physical mechanisms but also from enhanced grain boundary mobility induced by the presence of DP structures. Mechanical tests demonstrate that optimizing the grain structure and precipitate microstructure enables the alloy to achieve an exceptional combination of yield strength exceeding 2000 MPa and total elongation of approximately 18 %. Quantitative analysis reveals that precipitation strengthening, grain boundary strengthening, and dislocation strengthening are the primary contributors to enhanced yield strength. These findings deepen our understanding of the structure–property relationships in DP-strengthened alloys and provide practical guidance for designing advanced alloys with tailored mechanical properties through controlled microstructural evolution.