Nanosheet-structured B₄C with high hardness up to 42 GPa

High-quality bulk boron carbide (B₄C) is successfully prepared at high pressure and high temperature (HPHT) by using B₄C powder as a precursor. The as-synthesized B₄C possesses a nanosheet structure with a thickness value of 15 nm and a length of several dozen micrometers. Its Vickers hardness value and fracture toughness value are 42.4 GPa and 4.51 MPa·m^1/2, respectively, which are superior to those of B₄C obtained from spark plasma sintering due to its high densification and nanosheet structure. Additionally, it shows good property of oxidation resistance. In air, its oxidation resistance temperature is 1100 ℃ which is higher than that of diamond under the same test condition.