Overcoming strength-ductility trade-off in metastable CoCrFeNiAl0.5 high-entropy alloy by an eco-friendly electric pulse treatment (EPT)

Abstract

There is the urgent need for an eco-friendly, energy-efficiency and controllable approach to simultaneously enhance the strength and ductility of metastable multi-component alloy in the modern manufacturing era. Therefore, a study is devoted to bridge the gap between sustainability and mechanical properties. This work proposes an electric pulse treatment (EPT) method that significantly enhances the mechanical properties of as-cast metastable CoCrFeNiAl_0.5 high-entropy alloy (HEA), achieving a ∼19.1 % increase in yield strength with a remarkable ∼60 % ductility. After EPT processing, a heterostructure is achieved, which comprises dendritic-BCC, columnar-BCC, dispersed-BCC and matrix FCC structures. Compared to FCC phase, BCC structure is more sensitive to pulsed current. The EPT induces multi-scale microstructure evolution, including refined nanoprecipitation A2 particles in columnar-BCC, multiplication of dislocations in matrix, phase transformation based on diffusion of Al and Ni elements. This microstructure evolution process triggers the interaction dislocation with dispersed-BCC and A2 particles within different matrixes. As a result, Orowan and shearing mechanisms both contribute to enhanced strength, while the Orowan mechanism (∼141.5 MPa) governs precipitation strengthening. Furthermore, the strengthening mechanisms induced by EPT were quantitatively analyzed, which exhibited a better fit between the experimental and calculated results. The present findings provide an eco-friendly pathway for overcoming strength-ductility trade-off for as-cast metastable HEAs, thereby expanding the design possibilities for developing high-performance HEAs.