Study on microstructure and its formation mechanism, and mechanical properties of TiB2–TiC laminated Ti(C5N5) composite ceramic cutting tool material

•Two new layers were generated after sintering TiB2–TiC laminated Ti(C5N5) composite.•A laminated structure was ascribed to the element diffusion caused by C/N ratio among layers.•Ni-binder phase was rich in the diffusion layer.•Micro-laminated material exhibited a higher strength, a hard surface and a tough subsurface.•Ni-rich diffusion layer strengthened grain pulling-out and absorbed crack propagating energy.

TiB2–TiC laminated Ti(C5N5) composite ceramic cutting tool materials are prepared at the argon and vacuum sintering atmospheres respectively. The microstructure and mechanical properties of the composite are investigated. It is found that the composite includes the bulk and surface layer before sintering, while the new diffusion and transitional layers are formed after sintering. The Ni binder phase is rich in the diffusion layer, and the diffusion layer of the composite sintered at the vacuum atmosphere is narrower. The formation of layers is driven by the outward diffusion of the N element which results in the depletion of carbo-nitrides and the flowing of the melting Ni phase during the sintering. The composite exhibits the higher flexural strength and surface hardness than the monolithic Ti(C5N5) material. The Ni-rich diffusion layer acts as a tough subsurface in the composite, which can strengthen the effect of grain pulling-out as well as absorb the crack propagating energy. The flexural strength of the composite sintered at the vacuum atmosphere is slightly higher than at the argon atmosphere, while there are no obvious differences in the hardness and fracture toughness between these two composites.

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