https://link.springer.com/content/pdf/10.1007%2FBF02667204.pdf

The Fe-Ni (iron-nickel) system

Critical evaluation of the Fe-Ni, Fe-Ti and Fe-Ni-Ti alloy systems

The Fe–Ni system: Thermodynamic modelling assisted by atomistic calculations

The activity of carbon in the fcc solid solution of the Fe−Ni−C system has been measured at 800°, 1000°, and 1200°C by comparison with observed values in the Fe−C binary by equilibration with methane-hydrogen mixtures. Defining the lattice ratioz
 C≡n
 C/(n
 Fe+n
 Ni−n
 C), the activity coefficient ΨC≡a
 C/z
 C has been determined as a function of temperature and composition. At infinite dilution log ΨC goes through a maximum at about 70 pct Ni in agreement with Smith. The partial molar free energy of carbon in the dilute solution referred to graphite is not a linear function of the base alloy composition, but has a large deviation with maximum at about 60 pct Ni. Similar maxima occur in both ΔH
 C
 °
 and ΔS
 C
 °
 . Linear equations are derived for the activity coefficient of carbon in three composition ranges of Fe−Ni−C alloys; a simplified equation applicable to nickel steels is included. The solubility of graphite in nickel has been determined. The marked deviation from linearity is ascribed to the existence of iron atoms in two electronic states, γ1 and γ2 which differ in energy and are antiferromagnetic and ferromagnetic, respectively.

Thermodynamics of the Fcc Fe−Ni−C and Ni−C alloys

A thermodynamic assessment of the ternary Fe–Ni–Ti system together with a partial reassessment of the binary sub-systems Ni–Ti and Fe–Ti was made following the CALPHAD method and using the compound energy formalism (CEF). Two and four sublattices were used to model the bcc and fcc phases respectively. This allows describing the order–disorder transformations occurring not only in the ternary Fe–Ni–Ti system, but also in the quaternary Al–Fe–Ni–Ti system. The description of the C14 Laves phase TiFe2 was modified to three sublattices in order to be consistent with other Al–Fe–Ni–Ti sub-systems in which a three sublattice model is needed. Thermodynamic parameters were optimized using the available experimental data. On the basis of this optimization the stable phase diagram is calculated. Moreover stable and metastable equilibria between ordered and disordered phases based on fcc and bcc respectively are calculated.

Oswald Kubaschewski

Papers

Heats of formation and heat capacities in the system iron-nickel-chromium