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 multi-scale synergistic strengthening mechanism is revealed. At the atomic scale, unique interface engineering combines semi-coherent spinodal interfaces with incoherent precipitate interfaces. This activates micro-scale defect engineering by inducing high-density dislocations, nano-twins, and stacking faults. This multi-scale system constructs a composite structure at the meso-scale 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.

Traditional transition-metal carbide and nitride ceramics often exhibit a trade-off between hardness and toughness, leading to significantly reduced service life under severe conditions such as wear, corrosion, and high temperature. In this study, a spinodal decomposition-induced phasese paration strategy was employed to simultaneously enhance the hardness and toughness of (Ti, Zr)(C, N) carbonitride ceramics. Guided by thermodynamic calculations, a series of compositional variants of (Ti, Zr)(C, N) ceramics were synthesized, and the effects of aging temperature and duration on the microstructural evolution were systematically investigated. The experimental results demonstrate that spinodal decomposition induces the formation of a nanoscale phase-separated network, which strengthens the material while preserving fracture resistance. Furthermore, machine-learning models were developed to quantitatively correlate composition, microstructural features, and mechanical properties, enabling efficient screening and optimization of carbonitride ceramics. This work not only elucidates the intrinsic mechanisms by which spinodal decomposition enhances ceramic mechanical performance but also provides a data-driven framework for the rational design of high-performance ceramics for extreme environments.

Transition metal carbides exhibit outstanding mechanical properties but suffer from a critical hardness‒toughness trade-off. Spinodal decomposition-mediated phase separation, induced by high-temperature aging, is an effective strategy for enhancing the mechanical properties of carbide ceramics. However, the typically high stacking fault energy in carbide ceramics restricts the dislocation pinning effects of spinodal decomposition interfaces, hampering potential hardness and toughness improvements. Guided by first-principles calculations, this study employs (Ti,Zr)C carbide ceramics as a representative system and systematically lowers its stacking fault energy through nitrogen (N) incorporation. With optimized composition and controlled aging, distinct stacking faults emerged after short-term aging. As the aging time increased, these stacking faults progressively transformed into dislocation sources, facilitating dislocation multiplication. Mechanical testing revealed that samples incorporating 25% N followed by aging exhibited significant enhancements: The hardness and fracture toughness increased by approximately 40% and 50%, respectively, compared with those of the initial material. However, at higher N concentrations, excessive elastic strain energy accumulation induced lamellar thickening, diminishing the extent of improvement in hardness and toughness. This work designs a strategy to lower the stacking fault energy in carbide ceramics, overcoming its constraint on performance enhancement via spinodal decomposition and enabling hardness‒toughness synergy via spinodal decomposition through theoretical and processing solutions.