Production of Mo₂MB₂-type (M = Ni, Fe, Co) ternary boride containing alloys by self-propagating high temperature synthesis

In this study, the production of Mo₂MB₂ (M: Ni, Fe, and Co) ternary boride containing alloys from their oxides by aluminothermic self-propagating high-temperature synthesis (SHS) method was investigated. The influence of different initial reactant ratios on the concurrent synthesis of reinforcement and matrix phases was studied. The thermochemical modeling studies were conducted to estimate the adiabatic temperature (T_ad) change as well as high-temperature products. The phases, microstructure and chemical composition of the products were analyzed by X-ray diffraction, scanning electron microscopy (SEM) and atomic absorption spectroscopy (AAS) methods, respectively. It was found that, in the optimum conditions, the in-situ composite materials with Mo₂MB₂ as the reinforcement phases (i.e. Mo₂NiB₂, Mo₂CoB₂, or Mo₂FeB₂) and M₃Al/M₂₀Al₃B₆ intermetallic compounds as the matrix phases (i.e. Ni₃Al/Ni₂₀Al₃B₆, Co₂₀Al₃B₆, or Fe₃Al) can be synthesized by SHS method. Increasing both the B₂O₃/Al ratio (i.e. from 0.28 to 0.72) and M_xO_y/MoO₃ ratio (i.e. from 0.58 to 1.5) significantly decreased the residual Al content and increased ternary boride phases in the products. It was also revealed that the microhardness values of these SHS produced alloys can reach up to 1301 ± 162 HV.