Special mechanical properties of diboride ceramic composites with complex microstructures: comparative analysis of three study cases

Ceramics are hard and brittle materials. They are usually difficult to machine by chipping due to a strength-ductility trade-off. Moreover, their strength decreases at high temperatures. In this work, we review the peculiar features of three systems with unique mechanical properties. The MgB2 added with hBN (hexagonal BN) and G (graphene) is machinable by chipping and is assessed for bulk superconducting magnets. The second system is a TiB2-B4C structural ceramic composite (70/30 vol.) with a high bending strength of 1.1 GPa at 1800°C, showing an unusual shape of the bending strength–strain curve composed of elastic, ductile, and strengthening regions. The third system is the heterogeneous, multiphase high-entropy diboride (Ti0.25Ta0.25Hf0.25Zr0.25)B2. Remarkably, it demonstrates a deformation-resistant mechanism that persists with increasing temperature up to 1800°C. Ductile behavior (7.5% strain) is observed at 2000°C, while the bending strength (407 MPa) is 25% higher than at room temperature.