Thermodynamic properties of B2-AlFeNi alloys.: Part I:: Investigation by Knudsen effusion mass spectrometry

The vaporization of Al-Fe-Ni alloys has been investigated in the temperature range 1180 to 1508 K by Knudsen effusion mass spectrometry (KEMS). Fourteen different compositions were examined in the B2 region: 10 compositions at two fixed Al concentrations, X-Al = 0.45 and X-Al = 0.50 plus four extra compositions at constant X-Ni/X-Fe = 1. For the first time, reliable partial pressures and thermodynamic activities of Al, Fe, and Ni have been evaluated from the measured ion intensities for both the alloy and the pure element. Gibbs energies, partial molar enthalpies, and entropies of formation for all the components have also been obtained. The relative partial molar enthalpies and entropies were found to be nearly temperature independent over the wide temperature ranges investigated. At 1400 K, the Gibbs energy of formation of Al0.50Fe0.25Ni0.25 and Al0.45Fe0.275Ni0.275, with Al(liq), Fe(fcc), and completely paramagnetic Ni(fcc,cpm) as reference states, are -37.9 +/- 0.42 kJ/mol and -38.1 +/- 0.42 kJ/mol, respectively. At the same temperature, the enthalpies of formation of Al0.50Fe0.25Ni0.25 and Al0.45Fe0.275Ni0.275, with the same reference states, are -51.5 +/- 1.7 kJ/mol and -49.2 +/- 1.7 kJ/mol, respectively.