Role of copper on L12 precipitation strengthened fcc based high entropy alloy

A novel face-centered cubic (fcc)-based precipitation-hardenable high entropy alloy (HEA) or more broadly termed complex concentrated alloy (CCA) has been designed by coupling the beneficial effects of adding small amounts of Ti and Cu to the base alloy, Al0.3CoCrFeNi. While previous work has shown that large concentrations of Cu in fcc HEAs based on CoCrFeNi can lead to embrittlement, the present study clearly shows that in small amounts this alloying element can be quite beneficial, since Cu stabilizes the ordered L12 (gamma prime) phase, and acts as a heterogeneous nucleation site for this ordered phase within the fcc matrix. Additionally, Ti also stabilizes the L12 phase, increasing its volume fraction. This novel precipitation-hardened HEA/CCA, with a nominal composition of Al0.3Cu0.3Ti0.2CoCrFeNi, exhibits yield and ultimate tensile strengths of 820 MPa and 1100 MPa at room temperature respectively, while retaining a tensile ductility of nearly 20% and an extraordinarily high strain hardening rate ∼ 2700 MPa, a rather unique balance of properties for an fcc-based austenitic alloy. [Display omitted]