Microstructure and mechanical properties of TiB2-based composites with high volume fraction of Fe-Ni additives prepared by vacuum pressureless sintering

TiB2-based composites with high volume fraction of Fe-Ni as additive were fabricated by vacuum pressureless sintering. The effect of Fe-Ni addition (Fe:Ni=6:4) at different volume fractions from 20 to 35 vol% on the microstructure evolution and fracture behaviour of the TiB2-(Fe-Ni) composites was investigated. It was found that the TiB2-(Fe-Ni) composites consisted of only TiB2 and γ(Fe, Ni) phases without any brittle phases. The relative density, flexural strength and fracture toughness of the composites increased as the Fe-Ni content increased. The results indicated that the TiB2-35 vol% (Fe-Ni) composites exhibited the optimum combination of physical and mechanical properties, i.e., the relative density of 98.32%, the Vickers hardness of 8.56 GPa, the flexural strength of 1050.92 MPa and the fracture toughness of 17.75 MPa m1/2. The high fracture toughness of the TiB2-35 vol% (Fe-Ni) composite was due to an intensive coupled mechanism of the near-full density, dimple fracture of Fe-Ni phase, crack deflection, crack bridging, grain's pull-out and transgranular fracture of the TiB2 particles.