The nickel-rich region of the Ni-Ge phase diagram

Abstract

We present new results on the phase boundaries separating the single and the 2-phase regions of the Ni-rich Ni-Ge phase diagram. The accuracy of the boundary between the 2-phase Ni(Ge) + Ni 3Ge and single-phase Ni 3Ge region is reinforced by the addition of new data obtained from dissolution experiments. This boundary is consistent with the results of a recent thermodynamic model at temperatures lower than ∼840°C, but is leaner in Ge content at higher temperatures. Additional data on the equilibrium solubility of Ge in Ni (Ni 3Ge solvus) reinforces the accuracy of the phase boundary to temperatures as low as 700°C; these data are not new, but are not included in the most recent assessments. The recent thermodynamic model of the Ni 3Ge solvus is in remarkably good agreement with the experimental results. The composition dependence of the ferromagnetic Curie temperature, T c, is also re-evaluated by the addition of data not previously included in recent assessments. The dependency of T c on Ge content is essentially linear to concentrations of ∼13% Ge, which exceeds the solubility of Ge in Ni-Ge alloys. Empirical equations relating equilibrium compositions and temperatures of the phase boundaries and the composition dependence of T c are presented. © 2011 ASM International.