Critical Evaluation and Thermodynamic Optimization of the Al-P and Fe-Al-P Systems

Abstract

The Al-P system and Fe-Al-P system have been thermodynamically optimized using the CALculation of PHAse Diagrams (CALPHAD) method based on critical evaluation of all available experimental data. The liquid phases and solid solutions were modeled using the Modified Quasichemical Model and Compound Energy Formalism, respectively. The Gibbs energies of stoichiometric AlP compound and liquid Al-P solution were critically optimized to reproduce the melting point of AlP and the liquidus of Al-P system on the Al-rich corner. In the ternary Fe-Al-P system, the behavior of P in the liquid was also well optimized with introduction of Toop interpolation technique (Al as an asymmetric component). In addition, various phase equilibria of Fe-Al-P alloys containing up to 30 wt.%Al and 15 wt.%P, isothermal sections at 450, 650 and 800 °C, and the solubility of P in BCC_A2 Fe-Al alloys were excellently described, compared to experimental data. According to the present optimization, an accurate and consistent thermodynamic database of the Fe-Al-P system has been developed.