Fabrication and mechanical properties of Cr, V doped Mo2NiB2 hard materials based on crystallographic approaches

The effects of Cr or V substitution on the crystal structure and mechanical properties of Mo2NiB2 were investigated by experiments and first principles calculation. Mo2Ni1-xCrxB2 and Mo2Ni1-xVxB2 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 Mo2Ni1-xCrxB2 and Mo2Ni1-xVxB2 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 Mo2Ni1-xCrxB2 and Mo2Ni1-xVxB2 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 Mo2Ni1-xCrxB2 and tetragonal Mo2Ni1-xVxB2 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. © 2021 Japan Society of Powder and Powder Metallurgy