Hardness and compression behavior of niobium carbide

We report the combined experimental and theoretical investigations on high pressure structural stability of niobium carbide (NbC). The compressibility of NbC has been measured using angle-dispersive synchrotron X-ray diffraction in a diamond anvil cell (DAC) at room temperature and high pressure (up to 38.0 GPa), complemented with first-principles density-function theory calculations. The results imply that NbC shows bulk modulus of K0 = 281 (6) GPa with a pressure derivative K0′ = 6.2 (1.5) for its strong covalent bonding. In addition, indentation testing on the well-sintered bulk NbC obtained at 5.0 GPa/1400°C yielded a Vickers hardness of 19.2 GPa and fracture toughness of 7.7 MPa m1/2 at applied load of 10 kgf, demonstrating that binderless NbC prepared under high pressure should be a prospective hard material.