Multiscale chemical ordering heterogeneity facilitates exceptional strength and ductility in additively manufactured Ti-added AlCoCrFeNi2.1 high-entropy alloys at intermediate temperatures

The remarkable mechanical properties of high-entropy alloys at room and cryogenic temperatures have garnered significant attention in recent years. However, their poor mechanical performance at intermediate temperatures has hindered their practical application in many contexts. This study examines the effect of Ti addition on the intermediate-temperature tensile properties of additively manufactured AlCoCrFeNi₂.₁ eutectic high-entropy alloys. The findings demonstrate that Ti addition improves the alloy's tensile properties through several vital mechanisms. Ti addition significantly increases back-stress, which dominates strain-hardening behavior. At 400 °C, Ti addition promotes the formation of chemically long-range ordered and spinodal decomposition, facilitating multi-mode dislocation behavior characterized by coexisting planar and wavy slip. This enhances work-hardening, thereby achieving improved strength-ductility synergy. At 600 °C, the long-range ordered and spinodal decomposition evolved into nanoscale D0₃ precipitates that allow dislocation pinning and contribute to high strength while preserving good ductility. Moreover, Ti addition induces a rounded dual-phase microstructure, where the face-centered cubic phase serves as an adhesive layer, preventing crack propagation along the phase boundary. These mechanisms synergistically enhance strength and ductility at intermediate temperatures, making Ti-modified AlCoCrFeNi₂.₁ high-entropy alloys highly suitable for applications in the 400–600 °C temperature range.