Thermomechanical and thermal characterization of pressureless sintered TiB2

Abstract

The impact of high-energy milling using WCCo media on the pressureless sintering and properties of TiB₂ was studied. After 30 mins of milling, samples sintered at 2200 °C achieved a high relative density (>98 %) and a fine mean grain size (<2 µm). In the microstructure W_xB_y phases, often containing Co, were observed at triple points, due to contamination from the milling media. Moreover, core-rim structures with multiple rims were detected: the cores consisted of pure TiB₂ grains, the rims were (Ti_xW_y)B₂ solid solutions. The core-rim formation was significantly more pronounced compared to a reference sample of the same powder mixture densified by hot pressing at 1900 °C. The hardness reached 23 GPa, comparable to the hot-pressed sample, while the fracture toughness remained within 4.8–5.1 MPa·m^1/2 up to 1000 °C. The strength was approximately 350–400 MPa up to 1000 °C, declining sharply at higher temperatures due to W-containing impurities. Thermal diffusivity and conductivity were similarly impacted by these impurities.