Abstract: Ultrahigh-strength Cu-Ti alloys are considered ideal materials for next-generation elastic electronic components, but face a critical bottleneck among the strength, electrical conductivity, and plasticity. Here in this study, the synergistic effect of Ti and Fe elements optimized precipitation behavior and nanostructure, thereby overcoming the inherent strength-plasticity and strength-conductivity trade-offs in Cu-Ti alloys. Trace Fe additions promote dispersed nucleation of nanoscale β'-Cu₄Ti precipitates, leading to a significantly higher density and finer size of the strengthening phase. Atom probe tomography (APT) analyses reveal that the Fe initially co-precipitates with the β'-Cu₄Ti phase, subsequently segregating from the core toward the growth tips. The enrichment of Fe atoms significantly raises the diffusion energy barrier for Ti within the β'-Cu₄Ti phase, thereby facilitating sufficient precipitation of residual Ti solutes. The precipitation of nanoscale spherical Fe₂Ti phases is attributed to their favorable heterogeneous nucleation at the interfaces of β'-Cu₄Ti precipitates. The formation of primary Ti₂FeCu and TiFe phases refines the grain size of Cu-3Ti-0.2Fe alloy from 127 to 7 µm, and further reaches 310 nm after processing. After thermomechanical treatment, we report a 1228 MPa strength Cu-Ti-Fe alloy with improved conductivity and elongation to 16.8 %IACS and 5.5 %. The uniform nanocrystalline and the enhanced precipitation behavior of β'-Cu₄Ti phases contribute significantly to the comprehensive properties. This study leads us to reevaluate the synergistic effects between these two conductivity-detrimental elements and delivers a novel strategy for the development of conductivity and plasticity in ultra-high-strength Cu-Ti alloys.

Key words: Cu-Ti-Fe alloy, Ultra-high strength, Atom probe tomography, Precipitation behavior, High ductility and high conductivity