Strength–ductility synergy in NbTaTiV refractory high-entropy alloy composites via in-situ formation of TiC from NbC addition

Refractory high-entropy alloys (RHEAs) have emerged as promising candidates for high-temperature structural applications due to their exceptional thermal stability and mechanical performance. However, most RHEAs still face an inherent trade-off between high strength and limited ductility at room temperature. In this work, an alloy design strategy was employed to intentionally induce the in-situ formation of TiC through the decomposition of added NbC within a ductile NbTaTiV matrix, thereby achieving a synergistic enhancement in strength and ductility. NbTaTiV-based RHEAs were first prepared by arc melting under an argon atmosphere, and NbC was subsequently added through arc melting to produce high-entropy composites with varying NbC contents. The added NbC decomposed during melting, leading to the in-situ formation of TiC owing to its more negative free energy of formation than that of NbC, while the released Nb diffused into the solid-solution matrix. As a result, the crystal structure of NbTaTiV transformed from a single body-centered cubic (BCC) phase to a dual-phase (BCC + TiC) microstructure. The volume fraction of TiC increased with increasing NbC content, accompanied by a morphological transition from needle-like to blocky structure. The resulting NbTaTiV high-entropy composites exhibited an outstanding combination of strength and ductility, achieving yield strengths up to 2305 MPa with 10 % fracture strain. These results demonstrate that controlled in-situ carbide formation provides an effective pathway to tailor microstructures and achieve superior mechanical performance in RHEA systems for demanding structural applications.