Experimental Investigation and Thermodynamic Assessment of Ni–B and Ni–B–C Systems

As nickel-based heat-resistant alloys contain small amount of boron and carbon, it is imperative to study their phase diagrams and thermodynamic properties to understand the behavior of carbon and boron. In this study, the solubilities of carbon and boron at the face-centered cubic (fcc) and liquid phase transition temperatures of Ni–B and Ni–B–C systems were determined using the diffusion couple technique and differential scanning calorimetry. In addition, a thermodynamic assessment of the Ni–B, Ni–C, and Ni–B–C systems was conducted based on the results of previous studies and experiments of the current study. An associate model was employed for the liquid phase, and a compound energy model was employed for the fcc phase. The calculated results agreed well with the experimental data without the introduction of ternary parameters. Metastable two-phase separation in the liquid phase was predicted on nickel-rich side in the Ni–B system at low temperature, which can be related to the phase separation or compositional modulation of Ni–B amorphous alloys. Thus, the present model can reproduce the phase diagram of metal-boron systems.