Assessment of the Ti-Rich Corner of the Ti-Si Phase Diagram: The Recent Dispute About the Eutectoid Reaction

Abstract

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.

Assessment of the Ti-rich corner of the Ti-Si phase diagram using two sublattices to describe the Ti5Si3 phase

“…The shape of this phase field resembles a previous result, which described the Ti 5 Si 3 phase as Ti 3 Ti 2 (Ti,Si) 3 . Figure 2-b shows a detail of the Ti-rich corner near the eutectoid reaction, comparing the present assessment with previous experimental (Plitcha et al 1977;Plitcha and Aaronson, 1978) and calculated (Cost, 1998;Fiore et al 2016) phase diagrams. The present assessment showed smaller Si-solubility in the Ti(α) and Ti(β) phases when compared to the calculated phase diagram using COST 507 database (Cost, 1998) and a slightly higher value for the eutectoid temperature.…”

“…The other values were found for the β +Ti 5 Si 3 →Ti 3 Si, β→α+Ti 3 Si and β→α+Ti 5 Si 3 reactions, indicating that further experiments in these critical regions of the Ti-rich corner of the Ti-Si phase diagram are needed to improve the results of the present optimization procedures; and to define which one of the eutectoid reactions is actually the stable one (β→α+Ti 3 Si or β→α+Ti 5 Si 3 ). (Svechnikov et al 1970;Fiore et al 2016), except for the narrower solubility range of the Ti 5 Si 3 phase field. Figure 1-b shows a detail of the Ti-rich corner near the eutectoid reaction, indicating that there are no experimental data to validate the position of the calculated Ti(α) and Ti(β) solvus lines.…”

Suppression of Grain Boundary α Formation by Addition of Silicon in a Near-β Titanium Alloy

“…As the results, local oxygen concentrations at prior-¢ grain boundaries were reduced, resulting in the suppression of grain boundary ¡ formation. The role of titanium boride in scavenging oxygen seems to be similar to that of Ti 2 C. In the TiSi phase diagram, ¡ and ¢ phases are equilibrium with Ti 3 Si below 1444 K; 25) Ti 5 Si 3 is a metastable phase so that it is possible to work as a scavenger in Ti-170.3Si in this study. Figure 5 shows the Vickers hardness and tensile properties of Ti-170Si and Ti-170.3Si.…”

Preparation of Titanium Alloy/Bioactive Glass Composite for Biomedical Applications via Selective Laser Melting

“…The mole fractions of BG10 and BG30 for Ti:Si were 97.4:2.6 and 90.5:9.5, respectively. From the TiSi phase diagram, 31) Si mole fractions of 2.6 and 9.5 can form the Ti 5 Si 3 phase. In addition, the mixing enthalpies for TiAl, TiV, and TiSi were ¹30, ¹2, and ¹66 kJ•mol ¹1 , respectively.…”