CONSTITUTION AND THERMODYNAMICS OF FE-ND ALLOYS

The thermodynamic properties of Fe - Nd alloys have been determined be tween 973 and 1073 K by emf measurements on galvanic cells using CaF2 as a solid electrolyte. The activity of Nd in iron-rich solid solution alloys shows positive deviations from ideality. The Gibbs energies of the intermetallic compounds Fe17Nd2 and Fe17Nd5 were determined to be -46 and -52 kJ/mol, respectively, at 973 K. The thermodynamic behavio r of these and analogous alloys is interpreted by taking elastic and e lectronic effects into account. The phase relations of the Fe - Nd sys tem have been examined by X-ray diffraction and DTA. The limit of soli d solubility of Nd in Fe was determined to be 0.47 at.% Nd at 1073 K. Optimized descriptions of the phase diagram and the thermodynamic func tions of the Fe - Nd system have been obtained from experimental therm odynamic and phase diagram data using a computer program based on the least squares method. Optimized and experimental data are in good agre ement.