Achieving excellent strength-ductility synergy by adding carbon to a BCC structured low-cost Fe-based medium entropy alloy

Abstract

The microstructure and tensile properties of C-doped Fe-based medium entropy alloys with a single BCC structure were studied in this work. The addition of 0.25 at.% and 0.5 at.% C induces a significant transformation of the Fe64Ni11Cr15Si7Al3 alloy from a single-phase BCC to a dual-phase FCC + BCC structure, accompanied by the precipitation of B2 (NiAl) nanoparticles within the BCC phase. Following thermomechanical treatment, the (Fe64Ni11Cr15Si7Al3)99.75C0.25 alloy shows excellent tensile properties at 77 K, achieving a yield strength (YS) of 1550 ± 34 MPa, ultimate tensile strength (UTS) of 1926 ± 33 MPa, and uniform elongation (UE) of 25 ± 6 %. These properties are attributed to ultrafine grains, carbon solution, high-density dislocations, B2 (NiAl) nano precipitates, and transformation - induced plasticity (TRIP). At 298 K, the same alloy retains substantial mechanical performance with a YS of 1054 ± 14 MPa, UTS of 1203 ± 6 MPa, and UE of 15 ± 1 %, without the TRIP effect. In contrast, the (Fe64Ni11Cr15Si7Al3)99.5C0.5 alloy exhibits sudden fracture at 77 K, likely due to carbide formation. This work provides a novel strategy for overcoming cold working challenges in single BCC alloys, thereby promoting their development and potential applications in structural materials.

Keywords

• C-doping
• Fe-based medium entropy alloy
• Dual-phase
• B2 precipitations
• Tensile properties