Overcoming the strength-ductility trade-off of additively manufactured metastable high-entropy alloy via carbon doping

Interstitial carbon atom is key in modifying microstructures and enhancing mechanical properties of metastable high-entropy alloys. To hardness this potential, the microstructure, phase stability, stacking fault energy (SFE), and room-temperature mechanical properties of carbon-doped (Fe₅₀Mn₃₀Co₁₀Cr₁₀)_97-xSi₃C_x (x = 0~5 at.%) alloys fabricated by selective laser melting (SLM) were systematically investigated. Carbon addition can stabilize FCC solid solution structure and increase SFE, resulting into a deformation-induced transformation from being TRIP-dominated (x = 0, 1 at.%) to being TWIP-dominated (x = 3, 5 at.%). Carbon interstitial solid solution strengthening accounts for ~72% contribution to yield strength increment when carbon concentration reaches 3 at.%. Thus, the (Fe₅₀Mn₃₀Co₁₀Cr₁₀)₉₄Si₃C₃ alloy, compared to its carbon-free counterpart, exhibits remarkable simultaneous enhancements in mechanical properties, with yield strength of 615 MPa, ultimate tensile strength of 960 MPa, and fracture elongation of 38%. This suggests a superior strength-ductility synergy over most SLMed FCC high-entropy alloys and conventional alloys. Here, incorporating small-sized non-metallic elements into metastable high-entropy alloys through additive manufacturing provides an effective strategy to overcome the strength-ductility trade-off.