Synergistic strengthening mechanisms and multiple deformation behaviors of in-situ synthesized Al₂O₃ nanoparticles reinforced CoCrFeNiAl_0.3 high entropy alloy matrix nanocomposite with heterogeneous microstructure

The incorporation of nanoparticle reinforcements into high entropy alloy (HEA) has proven effective in improving the strength of face-centered cubic HEAs. However, this often results in a substantial loss of ductility. While a balance between strength and ductility can be achieved through multiple deformation mechanisms, these are typically triggered by extreme deformation conditions or by chemical composition manipulation. This study explores an alternative approach through heterogeneous microstructure architecture to activate multiple deformation mechanisms. Heterogeneities such as heterogeneous grains and nanoprecipitates were introduced into an in-situ synthesized Al₂O₃ nanoparticles reinforced CoCrFeNiAl_0.3 HEA nanocomposite via powder metallurgy and thermomechanical treatment processes. The research investigated the strengthening mechanisms and deformation behaviors under both quasi-static and dynamic deformation. Results revealed that the engineered heterogeneities facilitated multiple deformation behaviors. Stacking faults formed in ultrafine grains, while deformation twins and microbands formed in fine grains during quasi-static tension. Under dynamic compression deformation, dislocation cells, stacking fault networks, deformation twinning and HCP phase transformation occurred in fine grains. These mechanisms endowed the CoCrFeNiAl_0.3 HEA nanocomposite with exceptional mechanical performance, achieving a true stress of 1595 MPa and a true strain of 45.1 %. The enhanced stress-strain response prolonged the evolution of dislocation activities, ultimately enabling the transition from dislocation-microband interaction to the formation of dislocation cells.