Enhanced Strength and Plasticity of Selective Laser Melted NbMoTaW Refractory High-Entropy Alloy Via Carbon Microalloying

NbMoTaW refractory high-entropy alloy (RHEA) shows outstanding mechanical properties at ultra-high temperatures, while room-temperature brittleness limits its application. In this study, carbon (C) microalloying was employed to improve the room-temperature brittleness of NbMoTaW RHEA fabricated using selective laser melting (SLM). The addition of 0.5-at% C leads to good formability and remarkable microalloying effects. Nano-NbC precipitates distributed at grain boundaries and dislocations effectively refined the grain size. The yield strength, ultimate compression strength, and plasticity were successfully improved up to 1650 MPa, 1853 MPa, and 7.9%, respectively. Nano-NbC carbide precipitates in the form of diffusion transformation after SLM repeated heat input was verified by thermodynamics and kinetics calculations and in situ high-resolution thermal history observations. C microalloying endowed the alloy with remarkable enhancements of strength and plasticity by a combination of grain refinement and precipitation strengthening, which suggested a strategy for designing strong and ductile RHEA through SLM.