On the dissolution and enhancement mechanisms of Cr doping in Mo₂FeB₂-based cermets

In this work, the effect of Cr doping on the mechanical properties of Mo₂FeB₂-based cermets was studied. The results indicated that the hardness was continuously enhanced with the Cr contents, while the transverse rupture strength increased and then decreased. With the increase of Cr contents, the decreased binder deteriorated the fracture toughness. In the Mo₂FeB₂ particles of the cermets, Cr atoms mainly substituted the large-size Mo atoms instead of Fe. However, the first-principles calculation results showed that when the Cr atoms occupied the sites of Fe, the Cr-doped Mo₂FeB₂ were more thermodynamically stable. Based on the elemental composition of Cr-doped Mo₂FeB₂ bulks, the sites of Cr in Mo₂FeB₂ were mainly determined by the contents of Mo and Fe. In the Mo-depleted Mo₂FeB₂ bulk, Cr atoms preferred to substitute the Mo atoms, while Cr atoms occupied the sites of Fe in the Fe-depleted Mo₂FeB₂ bulk. Hence, the relatively lower content of Mo in Mo₂FeB₂-based cermets resulted in the substitution of Mo with Cr atoms. The intrinsic hardening of Mo₂FeB₂ induced by Cr doping contributed to the enhanced hardness of Mo₂FeB₂-based cermets. Besides, the decreased bulk modulus and shear modulus were conducive to the improvement of the transverse rupture strength.