The thermodynamic optimization of Ti-Si-X systems requires that their respective binary systems are constantly updated. The Ti-Si system has been experimentally investigated since the 1950s and these critical experimental data can be employed to calculate the Ti-Si phase diagram using thermodynamic modeling. The most recent assessment of the Ti-Si system was performed in 1998, showing the presence of stoichiometric Ti 3 Si as stable phase. In the light of the dispute over the stability of Ti 3 Si phase in the eutectoid reaction of the Ti-Si and Ti-X-Si systems, the present work assessed the Ti-rich corner of the "stable" (featuring Ti 3 Si phase) and "metastable" (featuring Ti 5 Si 3 phase) Ti-Si phase diagrams. The phase boundaries, the values of the error of the least-square method of the optimization procedure and the relative standard deviation of the calculated variables of the assessed diagrams; and previous investigations were discussed in order to inspire further experimental work on the eutectoid reaction of the Ti-Si phase diagram.

The thermodynamic optimization of Ti-X-Si systems requires that their respective binary systems be constantly updated. The most recent assessments of the Ti-Si phase diagrams used three sublattices to describe the Ti 5 Si 3 phase. The stable version of this phase diagram indicated the presence of Ti(β)+Ti 5 Si 3 →Ti 3 Si and Ti(β)→Ti(α)+Ti 3 Si reactions in the Ti-rich corner, while the metastable version featured the presence of a Ti(β)→Ti(α)+Ti 5 Si 3 reaction. The present investigation assessed these phase diagrams using two sublattices to describe the Ti 5 Si 3 phase in order to simplify the optimization of Ti-X-Si systems.

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