Processing and properties of reactively densified TiB2-AlN-hBN conductive ceramics with tunable compositions

Reactive sintering has been widely utilized to densify ceramics. Although the technology has numerous advantages, the composition of as-sintered ceramics is hard to be adjusted unless additional products are added. In this work, a novel solid-state route based on the reactions among TiN, Al and B were proposed to consolidate TiB2-AlN-hBN ceramics (TAB) with tunable compositions (hBN ≤ 42 vol%, AlN ≤ 45 vol%). Dense TAB with high relative density, refined grain size and homogeneous microstructure were obtained via spark plasma sintering at 1800 °C and 60 MPa. It was found that exothermic reactions between the reactants could be ignited during heating, and the order of temperature at which the combustion process occurred was just opposite to the sequence of adiabatic temperature for individual reactions. Effects of hBN and AlN amounts on the densification, microstructure, mechanical properties, machinability and electrical resistivity of as-sintered ceramics were comprehensively investigated. Compared to AlN, hBN content played a more obvious role on those properties. As hBN contents increased from 0 to 42 vol%, the flexural strength, fracture toughness, Vickers hardness and modulus of TAB continuously decreased. TAB with hBN amounts ≥ 13 vol% exhibited better machinability with surface roughness lower than 2.9 µm after machining. Nevertheless, their electrical resistivity values at room temperature fluctuated in a narrow range between 43 μΩ·cm and 83 μΩ·cm, irrelevant with the hBN amounts.