Effects of current density on the mechanical properties and microstructures of CoCrFeNiMn high-entropy alloy

Abstract

Electrically assisted forming has been a reliable method for enhancing the formability of metal components for decades. This study investigates the mechanical properties and microstructures of an equiatomic CoCrFeNiMn high-entropy alloy (HEA) under electrically assisted tensile (EAT). The results indicate that the CoCrFeNiMn HEA exhibits lower flow stress and elongation under EAT compared to samples deformed at room temperature (RT). The sample's temperature increases with current density, and the primary factor influencing the HEA's mechanical properties during EAT is the Joule heating effect. A model about yield strength (YS) increment is established to predict the YS of the HEA under EAT at different temperatures. As the amount of Joule heating rises, the dislocation width increases, reducing the lattice friction stress and resulting in an exponential decay of YS. Increased Joule heating caused by current leads to a higher dynamic recovery rate, resulting in a reduced proliferation rate of geometrically necessary dislocations. However, the change in dislocation recovery coefficients is little affected by the current density in CoCrFeNiMn HEA when the dynamic recovery produced by the current is not sufficient to increase the fracture strain. Deformation twins (DTs) form during deformation at RT and 10 A/mm2. However, as the current density surpasses 20 A/mm2, the flow stress becomes insufficient to induce the formation of DTs, leading to a decrease in strain-hardening ability and elongation. This study provides an experimental and theoretical foundation for forming HEA components.

Keywords

• High-entropy alloys
• Electrically-assisted tension
• Mechanical properties
• Strain hardening
• Deformation twinning