Experimental investigation and thermodynamic modeling of the ternary Ti–Fe–Mn system for hydrogen storage applications

The Ti–Fe–Mn alloys have attracted extensive interests due to the excellent hydrogen storage properties of the TiFe and TiMn2 (i.e. the C14 Laves phase) intermetallic compounds. The phase equilibria involving these two phases are essential for the design of hydrogen storage materials. In order to accelerate the design process, a thermodynamic description of the ternary Ti–Fe–Mn system was developed by experimental phase diagram study, ab initio calculations and CALPHAD-type thermodynamic modeling in the present work. The phase equilibria involving TiFe and C14 Laves phases were investigated by using electron probe microanalysis (EPMA). The partial isothermal sections at 1273 and 1373 K were established. Ab initio calculations were carried out to assist the determination of the thermodynamic parameters for the C14 Laves phase. The Ti-Mn system was re-assessed to reproduce the phase diagram data over the entire composition range. The Ti-Fe-Mn system was modeled and optimized based on reliable binary descriptions and experimental data. The TiFe and C14 Laves phases were well described to reproduce the phase equilibria with other phases in the ternary system. Moreover, the developed thermodynamic description of the Ti-Fe-Mn system was successfully applied for the prediction of phase constitutions of hydrogen storage alloys, demonstrating evidently the reliability of the practical use of present model parameters.