Abstract: Many precipitation-strengthened materials for elevated-temperature applications encounter substantial challenges with intermediate-temperature embrittlement, which is often associated with the formation of soft precipitate-free zones (PFZs) near grain boundaries (GBs). This research employs a novel double-aging strategy to trigger nanoprecipitation in the original PFZs, which establishes a dual-scale nanoprecipitate distribution in an L1₂-strengthened Co-Cr-Fe-Ni-Al-Ti high-entropy alloy (HEA) with a composition of Co_22.8Cr_18.0Fe_22.8Ni_27.4Al₅Ti₄ (at. %). The microstructure comprises unimodal nanoparticles in the original PFZs near GBs and a bimodal distribution of nanoparticles in grain interiors. The resulting alloy exhibits an exceptional yield strength of 780 MPa and an elongation of 35% at 650 °C. The formation of nanoparticles in the original PFZs enhances the strength and work hardening of PFZs, which decreases the strength mismatch between the grain interiors and GBs, thereby alleviating the strain localization at GBs. This mechanism not only promotes the coordinated deformation between PFZs and grain interiors but also facilitates the GB sliding, thereby remarkably enhancing the plasticity of the alloy. This approach holds promise for applications in various types of alloys and stands as an efficient method for addressing the intermediate-temperature embrittlement in high-temperature alloys.

Key words: High-entropy alloy, Precipitate-free zones, Nanostructure, Intermediate-temperature embrittlement