Hexagonal boron nitride-based composites: an overview of processing approaches and mechanical properties

Hexagonal boron nitride (h-BN)-based composites have been gaining prominence due to their versatile and significantly improved properties. For example they have good strength, better thermal conductivity, excellent resistance to thermal shocks and high temperatures, molten metal erosion resistance, ablation resistance, excellent machinability, good lubricating and chemical inertness. Owing to its excellent comprehensive properties, h-BN has significant potential applications in the fields of electronics, machinery, aerospace, nuclear energy, and metallurgy. Current article, first tries to critically review the literature, mainly published in the last decade, exploring the peculiar crystal structure and enhanced properties of h-BN and then various h-BN-based ceramics and its composites with oxides, nitrides, carbides, metals, and complex ceramics have been discussed based on their fabrication methods, mechanical properties, and the resultant applications. As per the reviewed results, hot pressing results in enhanced mechanical properties such as fracture toughness and flexural strength owing to the incorporation of BN by in situ reaction, which prevents BN agglomeration and reduces the size and quantity of defects. In contrast, the pressureless sintering method is reported to cause poor mechanical properties as compared to other fabrication methods of h-BN ceramics due to large porosity and poor bonding between h-BN grains caused by the forming of card room structure. Consequently, the green body's shrinkage is obstructed, and the expansion is occurred during the sintering process. All these aspects have been discussed in detail and they are the part of this review article.

Automated summary

Hexagonal boron nitride (h-BN)-based composites have versatile and significantly improved properties, making them highly valuable in various industries. This review article critically examines the crystal structure and enhanced properties of h-BN, as well as the fabrication methods, mechanical properties, and applications of h-BN-based ceramics and composites with different materials. The results show that hot pressing enhances mechanical properties through the incorporation of BN, while pressureless sintering leads to poor mechanical properties due to porosity and poor bonding between h-BN grains. These findings provide valuable insights for the development and application of h-BN-based materials.