Multiscale hardening and toughening of (Ti,Zr,V,Nb,Mo)C high-entropy carbides through coexisting phase separation and precipitation mechanisms

The engineering application of transition metal carbides is often constrained by the inherent hardness–toughness trade-off. While phase modulation is an effective strategy, the intrinsic brittleness of ceramics still limits the achievable toughening. Taking (Ti,Zr,V,Nb,Mo)C high-entropy carbide as a model system, this work proposes a novel strategy to reconcile this trade-off by leveraging synergistic phase separation and precipitation. The as-sintered single-phase solid solution was subjected to optimized aging treatment, yielding a microstructure characterized by coexisting spinodal decomposition domains and precipitates. Specifically, a multiscale synergistic strengthening mechanism is revealed. At the atomic scale, unique interface engineering combines semicoherent spinodal interfaces with incoherent precipitate interfaces. This activates microscale defect engineering by inducing high-density dislocations, nanotwins, and stacking faults. This multiscale system constructs a composite structure at the mesoscale where spinodal and precipitation domains coexist, effectively impeding dislocation motion and deflecting crack propagation. Driven by this mechanism, the material aged at 1300 °C for 20 h achieves an optimal synergy of properties, demonstrating concurrent increases in hardness (36%) and fracture toughness (45%) compared with the as-sintered state. This work opens a new avenue for designing advanced ceramic materials with superior damage tolerance.