Thermodynamic analysis of solid solution formation in the nanocrystalline Fe–Ti–Al ternary system during mechanical alloying

The nanocrystalline (Fe, Ti)3Al intermetallic compound was synthesized by mechanical alloying (MA) of elemental powders with the composition of Fe50Al25Ti25. The structural changes of powder particles during MA were studied by X-ray diffractometry. It was found that at early stages of MA, a nanocrystalline Fe(Ti, Al) solid solution is formed. This structure was transformed to disordered (Fe, Ti)3Al intermetallic compound at longer milling times. Thermodynamic analysis of this system revealed that in this ternary system, the least thermodynamic driving force for solid solution formation occurred for those compositions that contained 90% of one element. Fe substitution by Ti in Fe3Al compound decreased the Gibbs free energy change, resulting in a more stable structure.

► (Fe, Ti)3Al compound was synthesized by MA of Fe50A25Ti25 powder mixture.
► In Fe–Al and Al–Ti systems there is a driving force for solid solution formation.
► In Fe–Ti system in XFe = 0 to 0.15 compositional range there is no driving force.
► In Fe–Al–Ti) system least driving force appears at corners of triangle.
► Fe substitution by Ti in Fe3Al compound decreases the Gibbs free energy change.