Achieving sustainable strain hardening in a carbon-doped CuFeMnNi high-entropy alloy via dual-level heterogeneous microstructures

Phase decomposition is commonly observed in Fe-Cu alloy and Cu-HEAs that has been proved to harmful for the mechanical properties. Here we found that the phase decomposition based on the immiscibility be-tween Cu and Fe plays an active role in the mechanical properties of a carbon-doped face-centered-cubic (FCC) CuFeMnNi high-entropy alloy (HEA) while maintaining low raw-material costs, by employing only hot-forging and annealing. Upon annealing at 900 degrees C for 120 min, the annealed HEA exhibits dual-level heterogeneous microstructures, i.e., (i) the heterogeneous grain distribution composed of fine grains (<= 10 mu m) within the Fe-rich FCC1 phase and coarse grains (> 10 mu m) in the Cu-rich FCC2 phase, and (ii) special duplex phases characterized by the transitional region (similar to 1 mu m in thickness) at the junction of the above dual phases. Moreover, metastable FeMn-carbides in the FCC1 phase, chemical medium-range order, nano-twins, and 9R-martensite in the transitional region, as well as nanosized Cu-precipitates in the whole microstructure are detected. Compared with C-free CuFeMnNi HEAs, the present alloy exhibits satisfactory ultimate tensile strength around 800 +/- 10 MPa and excellent ductility of 56 +/- 1.14%. Sustainable strain hardening is achieved by sequentially triggering multistage strain-hardening mechanisms including hetero-deformation-induced hardening, precipitation hardening, and hardening jointly contributed by microbands, twins and dislocation cells. These findings open a new insight for regulating phase decomposition in Fe-Cu alloy and Cu-HEAs.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

Phase decomposition based on the immiscibility between Cu and Fe plays an active role in the mechanical properties of a carbon-doped CuFeMnNi high-entropy alloy. Annealing creates a dual-level heterogeneous microstructure with fine grains in the Fe-rich phase, coarse grains in the Cu-rich phase, and a transitional region at the junction. The alloy exhibits satisfactory ultimate tensile strength and excellent ductility, achieved through multistage strain-hardening mechanisms.