EXPLORING STRENGTHENING MECHANISMS OF ULTRAFINE-GRAINED Fe35Mn27Ni28Co5Cr5 HIGH-ENTROPY ALLOY PROCESSED BY SEVERE COLD ROLLING PROCESS

Abstract

This study describes the strengthening mechanisms of an ultrafine-grained (UFG) Fe₃₅Mn₂₇Ni₂₈Co₅Cr₅ high-entropy alloy (HEA) processed by severe cold rolling (SCR) process at room temperature. Microstructural evaluations were performed by field emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The findings demonstrated that the development of deformation microstructures consisted of a single face-centered cubic (FCC) phase with stretched grains along the rolling direction and lamellar deformation bands after a 90 % reduction in thickness. Using the Nix-Gao model, the dislocation density was determined by measuring the microhardness indentation size effect. The results indicated that an increase in rolling deformation leads to an increase in dislocation density. The dislocation density increased from 2.28 ×109 cm-2 for as-homogenized specimen to 8.65 ×109 cm-2 after 90 % reduction in thickness. The yield strength of the UFG Fe₃₅Mn₂₇Ni₂₈Co₅Cr₅ HEA was 5.2 times (1155 MPa) higher than that of the as-homogenized state (225 MPa). Finally, an assessment was conducted on the relative contributions of individual mechanisms, such as dislocation and grain refinement, to the strengthening of the Fe₃₅Mn₂₇Ni₂₈Co₅Cr₅ HEA.