Strengthening and toughening mechanisms of gradient Ti(C,N)-based cermets

Ti(C,N)-based cermets are promising for extreme service conditions owing to their high wear resistance and thermal stability, however, their application is often limited by intrinsic brittleness and low fracture resistance. In this study, a three-layer gradient Ti(C,N)-based cermet was fabricated by powder extrusion 3D printing followed by gas-pressure sintering, and the roles of the gradient structures in microstructural evolution and crack-growth behavior were elucidated. A pronounced compositional transition was achieved across the thickness, whereas each layer retained a stable core-rim microstructure with graded volume fractions of the metallic binder, rim, and core phases. The gradient progressively reduced lattice microstrain and promoted a fracture-mode transition from brittle to ductile. Cracks propagated predominantly in a straight transgranular manner in hard-phase-rich layers, whereas pronounced deflection, branching and ligament bridging occurred in binder-rich layers and at gradient interfaces, leading to a tortuous crack path and enhanced crack-growth resistance. The optimized cermet exhibited a microhardness of HV 20 , a fracture toughness of MPa·m 1/2 , and a flexural strength of MPa. This work provides a new theoretical framework and design approach for high-hardness and high-toughness cermets, and offers a methodical mechanistic understanding of the correlations among the gradient structure, the core-rim microstructure, and crack-propagation behavior.