Achieving high strength-ductility synergy in iron-rich medium -entropy alloy by structure change after heat treatment

Abstract

Iron-rich medium-entropy alloys have attracted significant research interest due to their cost-effectiveness. In previous work, most alloy properties were tuned by adjusting the elemental composition. However, this is not the sole method for regulating alloy properties. Thermo-Calc simulations indicated that these alloys could exhibit varying proportions of soft and hard phases in different solidified states, influencing their mechanical properties. Therefore, it is crucial to investigate the potential impact of subsequent heat treatment processes and secondary phase precipitation on the microstructure and mechanical properties of these alloys. A comprehensive study was conducted to characterize the microstructure and mechanical properties of both as-cast and heat-treated alloys. After annealing at 1300 °C for 1 h, followed by aging at 850 °C for 10 h, the as-cast alloy exhibited notable changes in phase composition: the FCC phase decreased from 83.66 ± 2.00 % to 78.80 ± 2.03 %, the BCC phase increased from 0.20 ± 0.05 % to 2.61 ± 0.01 %, and the B2 phase increased from 16.1 ± 0.25 % to 18.6 ± 0.01 %. These phase transformations resulted in an increase in the yield strength from 301.7 ± 5.0 MPa to 480.7 ± 13.6 MPa, accompanied by a decrease in elongation from 40.4 ± 3.0 % to 32.1 ± 1.8 %. The enhancement in yield strength was primarily attributed to the homogeneous precipitation of the B2 phase within the FCC matrix. These findings provide valuable insights for the optimization of heat treatment processes in iron-rich medium-entropy alloys.