Nanoprecipitate and stacking fault-induced high strength and ductility in a multiscale heterostructured high-entropy alloy

Two-phase high-entropy alloys (HEAs) have high strength due to the contribution of interface-dependent strengthening, but the deformation incompatibility between the two phases causes instability. The initiation of cracks occurs at the two-phase interfaces, which ultimately leads to low ductility. To overcome this problem, the strategy proposed in this work is to introduce nanoprecipitates as a buffer zone and simultaneously promote stress release caused by the formation of stacking faults (SFs) at the two-phase interfaces, reducing the stress localization at the two-phase interface, thus improving the ductility. The Al16Cr20Fe10Co30Ni24 HEA was chosen as the model material to evaluate this approach. After rolling at 800°C, the HEA had a two-phase lamellar structure consisting of a face-centered cubic (FCC) phase and an ordered body-centered cubic BCC (B2) phase. Recrystallization occurred within the FCC phase, and precipitates were present in both the FCC and B2 lamellae. The B2 nanoprecipitates in the FCC phase play the most important role, contributing to the improvement of yield strength and buffering the direct contact between gliding dislocations and the two-phase interface. In addition, the B2 nanoprecipitates also promote the widespread formation of SFs at the two-phase interfaces, leading to stress release. More importantly, nanoprecipitates are nucleation sites for SFs. The formation of an SF network improves the strain-hardening ability. The HEA shows a yield strength of 1,120 MPa and an ultimate tensile strength of 1,540 MPa while still exhibiting an elongation to fracture of ∼25%.