Microstructure, mechanical properties and corrosion resistance of Mo₂FeB₂-based cermets with different contents of Cr and Ni in chloride-ion-rich environment

Abstract

Mo₂FeB₂-based cermets with combined additions of Cr and Ni were prepared by reaction boronizing sintering. The effects of Cr and Ni content on the microstructure, mechanical properties, and corrosion behavior of Mo₂FeB₂-based cermets were systematically investigated. Increasing the Cr content enhanced the wettability between the hard phase and the Fe-based binder phase, resulting in a more homogeneous and densified microstructure, which, in turn, improved mechanical properties. However, excessive Cr led to hard-phase agglomeration and pore formation, thereby degrading mechanical performance. The addition of Ni lowered the liquidus temperature, enhancing liquid-phase flow during sintering. Nonetheless, excessive Ni caused microstructural agglomeration, which reduced the overall mechanical performance. Optimal mechanical properties were achieved with 9 wt% Cr and 3 wt% Ni, characterized by well-distributed hard phases and low porosity. Cr was enriched in the binder phase, forming a Cr-rich passivation film under chloride-rich conditions which suppressed galvanic corrosion. Ni further stabilized the passive film on the surface. The synergistic effect of Cr and Ni significantly enhanced corrosion resistance while simultaneously preserving excellent mechanical properties. Under neutral salt spray exposure, the corrosion process progressed through stages of film breakdown, pseudo-passivation and surface reactivation. Electrochemical impedance spectroscopy (EIS) analyses showed a gradual decline in the film resistance (R_f), the emergence of dual time constants, and increased double-layer capacitance (Q_dl), indicating a shift from film-controlled to substrate-controlled corrosion.