Nitrogen-induced stacking fault energy reduction enables spinodal-decomposition-driven toughening in (Ti,Zr)C ceramics

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.