Substitution Effects on the Crystal Structure and Nano-Micro Hardness of the Mo<sub>2</sub>NiB<sub>2</sub>-Ni Cermets

Mo2NiB2–Ni cermets have been studied by substituting transition metals at the Mo2NiB2 phase metal site to enhance their mechanical properties. Substituting Cr and V changes the crystal structure of Mo2NiB2 from orthorhombic to tetragonal, resulting in improved mechanical properties. However, the correlation between crystal structure alteration and mechanical property enhancement remains unclear. In this study, we investigated the nano–submicron hardness of Cr- and V-substituted Mo2NiB2–Ni cermets using nano-indentation and first-principles calculations to assess the chemical bonding in the Mo2NiB2 phase. Mo2NiB2-Ni cermets with a excess Ni binder phase was synthesized, which contains orthorhombic, tetragonal, and Ni phases. Nano-indentation results reveal significantly higher hardness in the tetragonal Mo2NiB2 phase, consistent with crystal orbital Hamilton population (COHP) analysis and integrated crystal orbital Hamilton population (ICOHP) values.