Thermodynamic assessment of Ni–B phase diagram

Abstract

The available experimental observations on the equilibrium phase diagram and on the mixing thermodynamics of the Ni–B system have been compiled and critically evaluated. An internally consistent set of thermodynamic model parameters for the solution phases as well as for the intermetallic compounds has been estimated by means of a least squares method and the Lukas program, simultaneously using phase diagram and thermodynamic observations. The complete phase diagram from pure boron to pure nickel at 600–2100°C was calculated using a thermodynamic approach and the thermodynamic mixing properties of the solution phases, as modelled by Redlich–Kister polynomials. The Gibbs energies of formation of the intermetallic phases, described as stoichiometric compounds, have been estimated from the experimental data and refined by means of a least squares treatment. No reliable observations are available on the alloys above 60 at.-%B and, thus, an extrapolated phase diagram has been calculated for the boron rich composition range. All the thermodynamic parameters obtained in the present estimation and used in the calculations are reported in numerical form.

MST/1657