The phase stability and mechanical properties of Nb–C system: Using first-principles calculations and nano-indentation

Structural stability and mechanical property of niobium carbide (NbC) were characterized by combined experimental methods and first-principles technique. The hardness and Young’s modulus were measured to be 24.5 GPa and 406 GPa for NbC from nano-indentation, respectively. Moreover, the systematically studies of the structural, mechanical, and electronic properties of niobium carbides show that pnma-Nb2C and P31-Nb6C5 are the ground state structures, consistent with the experiment results. The proposed Fm-3m-Nb23C6, Pnma-Nb3C, C2/c-Nb5C2, and P63mc-Nb7C3, are stable energetically, mechanically, and dynamically from first-principles calculations. The effects of carbon content on the elastic modulus and theoretical hardness of niobium carbides were also discussed.

► Hardness and Young’s modulus of c-NbC have been evaluated by nano-indentation.
► The properties of Nb–C system have been studied by first-principles calculations.
► Pnma-Nb2C and P31-Nb6C5 are identified as ground state structures for Nb–C system.
► Four proposed Nb-C phases are stable energetically, mechanically, dynamically.