Ti(C,N)-based cermets with strengthened interfaces: Roles of secondary cubic carbides

Core-rim structure, concerning its interface structure and internal stress, plays an important role in mechanical performance of Ti(C,N)-based cermets. Four types of cermets containing equimolar TaC, VC, ZrC, and NbC were fabricated, in order to reveal the synergetic relationship between core-rim structure and mechanical properties. VC and ZrC effectively inhibited the grain growth, while TaC and NbC favored for coarser core-rim grains. A thin distortion layer at the rim-binder interface was confirmed, formed during the solidifying stage. Compared to the TaC, ZrC and NbC, VC shrunk the lattice parameters of rims and effectively decreased the lattice misfit of the distortion zone from around 4.0%-0.8%. Cermets containing VC showed satisfactory bending strength of 2099 MPa and toughness of 10. 3 MPa m^1/2, owing to the strengthened rim-binder interface. TaC and NbC exhibited the similar roles in cermets with comparable mechanical properties, while addition of ZrC increased the lattice misfit of core-rim structure, resulting in poor mechanical performance. Decreased lattice misfit of rim-binder interface changed the fracture mode of cermets from intergranular to transgranular fracture, with in-situ formed dimples.