Design and fabrication of TiB2–TiC–Al2O3 gradient composite ceramic tool materials reinforced by VC/Cr3C2 additives.

In this study, TiB 2 –TiC–Al 2 O 3 gradient composite ceramic tool materials reinforced by VC/Cr 3 C 2 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/Cr 3 C 2 on the grain size were analysed, and it was found that VC/Cr 3 C 2 inhibited TiC dissolution and accelerated Al 2 O 3 re-precipitation, which in turn refined the TiC grains and coarsened the Al 2 O 3 grains. Consequently, crack deflection and intergranular fracture occurred around the TiC grains, whereas trans -granular fracture occurred inside the TiB 2 and Al 2 O 3 grains because rapid Al 2 O 3 precipitation facilitated TiB 2 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. [ABSTRACT FROM AUTHOR]