Fabrication and Mechanical Properties of Cr, V Doped Mo₂NiB₂ Hard Materials Based on Crystallographic Approaches

Abstract

The effects of Cr or V substitution on the crystal structure and mechanical properties of Mo₂NiB₂ were investigated by experiments and first principles calculation. Mo₂Ni_1-xCr_xB₂ and Mo₂Ni_1-xV_xB₂ samples were synthesized via the powder metallurgy method. The XRD analysis revealed that the tetragonal Mo₂NiB₂ phase appeared with the addition of the Cr or V in both Mo₂Ni_1-xCr_xB₂ and Mo₂Ni_1-xV_xB₂ samples, and increased with the increase of the Cr or V content x. Orthorhombic Mo₂NiB₂ phase decreased with the increase of the Cr or V content x, and completely disappeared at x = 0.75. The Vickers hardness of Mo₂Ni_1-xCr_xB₂ and Mo₂Ni_1-xV_xB₂ samples improved with increasing Cr or V additions, and the maximum values of 20.4 GPa and 19.8 GPa for x = 0.75 samples, respectively. The calculated shear modulus of the tetragonal Mo₂Ni_1-xCr_xB₂ and tetragonal Mo₂Ni_1-xV_xB₂ increase with increasing Cr or V content x. The calculated Vickers hardness of orthorhombic Mo₂NiB₂, tetragonal Mo₂CrB₂ and tetragonal Mo₂VB₂ are 21.915 GPa, 22.492 GPa and 24.656 GPa, respectively. The Crystal Orbital Hamilton Population (COHP) analysis indicates the excellent mechanical properties of tetragonal Mo₂CrB₂ and tetragonal Mo₂VB₂ are due to the strong bonding between Mo-(Cr or V) and (Cr or V)-B atoms.