Abstract
In this study, TiB2–TiC–Al2O3 gradient composite ceramic tool materials reinforced by VC/Cr3C2 additives were prepared through vacuum hot-press sintering. The effects of gradient combination, thickness ratio and sintering process (sintering temperature and soaking time) on the mechanical properties and microstructures of the composites were investigated. The results showed that the high surface compressive stress produced by the adequate gradient combination and thickness ratios refined the grains and increased the crack growth path. By comparison, the sintering temperature and soaking time influenced the grain size and porosity. In addition, the effects of VC/Cr3C2 on the grain size were analysed, and it was found that VC/Cr3C2 inhibited TiC dissolution and accelerated Al2O3 re-precipitation, which in turn refined the TiC grains and coarsened the Al2O3 grains. Consequently, crack deflection and intergranular fracture occurred around the TiC grains, whereas trans-granular fracture occurred inside the TiB2 and Al2O3 grains because rapid Al2O3 precipitation facilitated TiB2 grain growth. The optimum mechanical properties were hardness of 23.59 GPa, fracture toughness of 7.45 MPa m1/2, and flexural strength of 764.11 MPa.
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