Experimental investigation and thermodynamic modeling of the Mo-Co-B ternary system

Among the ternary borides, the Mo-Co-B system is of great interest because of its excellent hardness, toughness, and stability performance. Eight samples with 60 at.% Co were designed to investigate the isothermal section of Mo-Co-B system at 1073 K in the Co-rich portion. Scanning electron microscopy, energy-dispersion spectroscopy, electron probe microanalysis, differential scanning calorimetry, and X-ray diffraction were used to investigate the phase equilibria of the samples. The formation enthalpies of the ternary borides were obtained by first-principles calculations to serve as key information for thermodynamic assessment. By coupling the reviewed experimental data from the literature, the presently determined phase equilibria, and the calculated formation enthalpies of the compounds, the thermodynamic parameters for the Mo-Co-B ternary system were optimized and used to calculate the isothermal sections, vertical section, and liquidus projection of the system. Comprehensive comparisons showed that the calculated results are in reasonable agreement with the reported phase diagram and thermodynamic data.

Automated summary

By combining experimental data, phase equilibria determination, and calculated formation enthalpies, the thermodynamic parameters of the Mo-Co-B ternary system were optimized to calculate the isothermal sections, vertical section, and liquidus projection, showing reasonable agreement with reported phase diagrams and thermodynamic data.