Effects of TiB2 particle size on the microstructure and mechanical properties of TiB2-based composites

Abstract

TiB2–25 vol% (Fe-Ni) and TiB2–30 vol% (Fe-Ni) composites with different TiB2 particle size were fabricated by vacuum pressureless sintering at 1700 °C for 1 h. The influences of TiB2 particle size on the microstructure and mechanical properties was studied in detail. The phase analyses and microstructure of TiB2-based composites were investigated by X-ray diffraction, SEM, EPMA, and TEM. The experimental results showed that only TiB2 and γ(Fe, Ni) phases in the TiB2-based composites, not any other brittle phases such as M2B, M23B6 can be found. The morphology of raw TiB2 particles was irregular, however, many hexagonal crystals TiB2 grains were observed after sintering. The change of dominant fracture mode was strongly affected by the grain size of TiB2 particles, and the dominant fracture mode of TiB2-based composites transformed from trans-granular fracture to inter-granular fracture as the TiB2 particle size increasing from 1.97 to 4.27 µm. The high-toughness of TiB2-based composites was due to the synergetic action of comprehensive toughening mechanisms, including crack deflection, crack branching, as well as the strong bonding strength between TiB2 grains and γ(Fe, Ni) binder, etc. As TiB2 particle size increasing from 1.97 to 4.27 µm, the relative density, Vickers hardness, flexural strength, and fracture toughness of the TiB2-based composites decreased. The relative density, Vickers hardness, flexural strength and fracture toughness of TiB2–30 vol% (Fe-Ni) composites with the TiB2 particle size of 1.97 µm reached up to 98.20 ± 0.20%, 14.00 ± 0.40 GPa, 1000 ± 30 MPa, and 19.26 ± 0.72 MPa m1/2, respectively.