Strengthening Fe50+xMn25Cr15Ni10-x medium-entropy alloys by Ni/Fe replacement: Experiments and molecular dynamics study

The effect of replacing Ni by Fe on the microstructure and mechanical properties of Fe50+xMn25Cr15Ni10-x (x = 0, 4, and 8 at.%) medium-entropy alloys (MEAs) at 298 K and 77 K were investigated. The experimental results demonstrate that all the MEAs have a single-phase face-centered cubic (FCC) microstructure. The yield strength (YS), and ultimate tensile strength (UTS) of the MEAs remarkably increase with the Ni content decreasing at 298 K and 77 K, while their ductility slightly decreases. The Fe54Mn25Cr15Ni6 MEA has optimized mechanical properties, its YS, UTS, and ductility at 298 K/77 K are 381MPa/675 MPa, 643MPa/1179 MPa, and 50%/45%, respectively. The findings of molecular dynamics simulations reveal that as the Ni concentration decreases, the dislocation density and dislocation interaction increase. After the deformation at 77 K, there are stacking fault, deformation twin, and hexagonal close-packed phase in the MEAs, and their interaction strength increases with Ni concentration decreases. The present findings may provide a guide for the designing Fe-rich MEAs with reduced Ni content and superior performance.