Ab initio-based prediction and TEM study of silicide precipitation in titanium

The literature contains many contradictory data about the most thermodynamically favorable structure of precipitates in α -Ti matrix of the hypoeutectoid Ti–Si alloys. In this work we applied our recently developed thermodynamic model to predict the structure of Ti–Si precipitates in α -Ti matrix of the Ti–Si alloy with total Si concentration of 0.7 wt.%. We considered all prominent Ti–Si phases such as Ti 3 Si , Ti 5 Si 3 , Ti 5 Si 4 , TiSi and two TiSi 2 phases and discovered that formation of the Ti 5 Si 3 phase is more favorable than that of the Ti 3 Si in contradiction with the known phase diagrams. Theoretical result was confirmed by experimental investigation of microstructure and phase composition of the model Ti–0.7Si alloy annealed at 873 K for 10 h. Indeed, the only observed phase has hexagonal Ti 5 Si 3 structure. To ensure the completeness of the results we calculated ab initio elastic constants for all considered Ti–Si phases.