Double-peak precipitation hardening in the Cu-Fe-Ti alloy

A double-peak precipitation hardening is observed in a simple one-step cold rolled Cu-0.75Fe-0.35Ti alloy upon aging at 500 °C, in which an early hardness peak (aging for 1 h) appears preceding the second one (aging for 6 h). Transmission electron microscopy observation reveals that profuse coherent precipitates keeping large lattice mismatch with matrix are formed in the 1 h-aged specimen, resulting in a strong coherency strengthening and accounting for the early hardness peak. With aging time increasing to 6 h, the precipitates evolve into incoherent Fe2Ti/FeTi precipitates and strengthen alloy through the Orowan bypass mechanism, responsible for the second hardness peak. Finally, the 1 h-aged CRA specimen shows a higher hardness (181.2 HV) than the 6 h-aged one (174.8 HV) while a comparative electrical conductivity (56.8%IACS) as the 6 h-aged one (59.8%IACS). Our findings provide the possibility to design high-performance Cu-Fe-Ti alloy with coherent precipitates through a rapid process.