Sintering mechanism, microstructure evolution and nanomechanical properties of Cr-added Mo₂FeB₂ based cermets

Mo₂FeB₂ based cermets with xCr (x = 0, 3, 6, 9, 12, weight %) contents were fabricated via reaction boronizing sintering strategy. Effects of Cr addition on sintering mechanism, microstructure evolution, and nanomechanical properties of Mo₂FeB₂ based cermets were investigated. Results indicate that the addition of Cr decreased reaction temperatures of solid-phase and liquid-phase reactions in sintering process. Moreover, relatively small grain size of Mo₂FeB₂ hard phase and maximum relative density of Mo₂FeB₂ based cermets were obtained at 9 wt% Cr content. Besides, Cr atoms replaced partial Mo atoms in Mo₂FeB₂ hard phase and partial Fe atoms in Fe binder phase, respectively. In addition, the Mo₂FeB₂ grains transformed from anisotropic shape to isotropic shape with Cr solution. High resolution TEM revealed that with Cr addition, interplanar distance of Mo₂FeB₂ crystal decreased, while interplanar distance of Fe crystal increased. More edge dislocations and lattice distortions occurred in cermets with 9 wt% Cr content as compared with Mo₂FeB₂ based cermets without Cr. Furthermore, intrinsic hardness, elasticity modulus, and resistance to plastic deformation of Mo₂FeB₂ hard phase and Fe binder phase enhanced with Cr content increasing from 0 wt% to 12 wt%. However, intrinsic toughness decreased in the process.