The Influence of Carbon and MoSi2 Addition on the Sinterability and Mechanical Properties of Titanium Boride (TiB2) Based Composites

Titanium boride (TiB2) is a material classified as ultra-high temperature ceramics. The TiB2 structure is dominated by covalent bonds, which gives materials based on TiB2 very good mechanical and thermal properties, but also makes them difficult to sinter. Obtaining dense TiB2 polycrystals requires chemical or physical sintering activation. Carbon and molybdenum disilicide (MoSi2) were chosen as sintering activation additives. Three series of samples were made, the first with carbon additives: 0 to 4 wt.%; the second with 2.5, 5 and 10 wt.%. MoSi2 and the third with both additions of 2 wt.% carbon and 2.5, 5 and 10 wt.% MoSi2. MoSi2. On the basis of dilatometric sintering analysis, all additives were found to have a favourable effect on sinterability of TiB2, and it was determined that sintering of TiB2 with carbon addition can be carried at 2100°C and with MoSi2 and both additives at 1800°C. The polycrystals were sintered using the hot pressing technique. On the basis of the studies conducted in this work, it was found that addition of 1 wt.% of carbon allows to obtain single-phase TiB2 polycrystals of high density (>90%). The minimum MoSi2 addition required to obtain dense sinters with a cermet-like microstructure was 5 wt.%. High density was also achieved by materials containing both additives. Samples with higher MoSi2 content, i.e. 5 and 10% showed densities close to 100%. Mechanical properties such; as Young's modulus, hardness and fracture toughness (KIc) of the polycrystals and composites were similar for samples with densities exceeding 95%. The Vickers hardness was 23 to 27 GPa, the fracture toughness (KIC) was 4 to 6 MPa·m0.5 and the Young's modulus was 480 to 540 GPa. The resulting TiB2-based materials showed potential in high-temperature applications.