Thermodynamic activities in the alloys of the Ti-Al system

The vaporization of the solid alloys of the Ti-Al system has been extensively studied for the complete composition range of the system by using Knudsen effusion mass spectrometry at temperatures between 1113 and 1664 K. 19 alloy samples of different compositions covering the complete composition range were investigated and their Ti and Al partial pressures determined. Thermodynamic activities and chemical potentials of Ti and Al as well as Gibbs energies were evaluated for a temperature of 1473 K. Two independent methods were used for the determination of the Ti activities yielding consistent results. The large temperature range of the partial pressure measurement for three alloys in the homogeneity range of the TiAl phase rendered possible the determination of partial and integral thermodynamic functions (Delta H, Delta G) for the formation of this phase. The data obtained are discussed.