Pulsed electrodeposition of homogenous and heterogeneous solid solution layered structure in high strength nanocrystalline CoCu alloys

A supersaturated solid solution nanostructure of an immiscible CoCu system is among the promising nanocrystalline (NC) alloys offering enhanced thermal and mechanical stability. In this paper, experiments were conducted to study the phase transformation and tailoring microstructure from a homogeneous/single-phase to a heterogeneous/dual-phase solid solution layered CoCu nanostructure via pulsed electrochemical deposition (PED). The increasing concentration of sodium dodecyl sulfate (SDS) in electrolyte played a crucial role in stabilizing a homogeneous solid solution CoCu nanostructure. On the other hand, the opposite approach led to the formation of heterogeneous solid solution CoCu alloys in the form of multilayered nanostructure consisting of the primary and secondary solid solution CoCu differing in 10–15 at.% Cu. The separation of primary and secondary phase is more prominent with the extended pulsed periods. The mechanical properties of selected single- and dual-phase alloys were investigated through micro-pillar compression, revealing that a combination of a high yield strength and an elevated strain hardening can be achieved in NC materials through a combined solid solution strengthening and hardening through nano-twin (NT).