Synthesis and crystal structure of Mo2Ni1-Cr B2 hard materials

Boride-based cermets possess attractive mechanical properties and are promising candidates for hard materials. Mo2NiB2–Ni-based cermet, which is a boride-based cermet, exhibits high hardness and attractive transverse rupture strength (TRS) properties through the crystal structure deformation that is caused by Cr or V substitution of Ni in the Mo2NiB2 phase. In this study, the effects of Cr substitution on the crystal structure, mechanical properties, and consistency were investigated. Cr-substituted Mo2Ni1-xCrxB2 samples were synthesized via the powder metallurgy method. A first-principle calculation was also conducted to obtain the bulk modulus of the Cr-substituted Mo2Ni1-xCrxB2. With the increase of the Cr content x, the tetragonal-Mo2NiB2 phase appeared, while the orthorhombic Mo2NiB2 phase disappeared. In the x = 0.6 samples, the Mo2Ni0.4Cr0.6B2, tet-Mo2NiB2 phase was observed. According to the Rietveld analysis, substituted Cr atoms occupied the Ni and Mo sites in the tet-Mo2NiB2 structure. The Rockwell A-scale hardness (HRA) measurement was performed to investigate the effects of the Cr content on the mechanical properties. The HRA values increased with the Cr content, and the maximum HRA value was approximately 87.1 for the x = 0.6 sample. The bulk modulus was also affected by the Cr content x in Mo2Ni1-xCrxB2, and the maximum value was attained at x = 0.75.