Abstract
Transparent ceramics are used in new technology because of their excellent mechanical properties over glasses. Transparent ceramics are nowadays widely used in armor, laser windows, and in high temperature applications. Silicon nitride ceramics have excellent mechanical properties and if transparent silicon nitride is fabricated, it can be widely used. h-BN has a lubricating property and is ductile. Therefore, adding h-BN to silicon nitride ceramics gives a lubricating property and is also machinable. Translucent silicon nitride was fabricated by hot-press sintering (HPS) and 57% transmittance was observed in the near infrared region. A higher wt. % of h-BN in silicon nitride ceramics does not favor transparency. The optical, mechanical, and tribological properties of BN dispersed polycrystalline $Si_3N_4$ ceramics were affected by the density, ${\alpha}:{\beta}$-phase ratio, and content of h-BN in sintered ceramics. The hot pressed samples were prepared from the mixture of $\alpha-Si_3N_4$, AlN, MgO, and h-BN at $1850^{\circ}C$. The composite contained from 0.25 to 2 wt. % BN powder with sintering aids (9% AlN + 3% MgO). A maximum transmittance of 57% was achieved for the 0.25 wt. % BN doped $Si_3N_4$ ceramics. Fracture toughness increased and wear volume and the friction coefficient decreased with an increase in BN content. The properties such as transmittance, density, hardness, and flexural strength decreased with an increase in content of h-BN in silicon nitride ceramics.
