Experimental and calculated Ti-rich corner of the Al-Si-Ti ternary phase diagram

Abstract The phase equilibria between β(bcc), α(hcp), Ti 3 Al-α 2 (hcp) and Ti 5 Si 3 (hcp) in the Ti-Al-Si system have been investigated in the temperature range of 700 to 1200°C. Isothermal sections of the ternary phase diagram have been assessed employing thermodynamic software, which uses the compound-energy model to describe mathematically the phase. Available experimental phase equilibria results on the Ti-Al-Si system were used to calculate missing binary and ternary interaction parameters and assess isothermal phase diagrams. Extrapolations in the resulting tie-triangles indicate the existence of three eutectoid reactions in the Ti-rich corner of the ternary diagram: β −⪢ α + Ti 5 Si 3 , α −⪢ α 2 + Ti 5 Si 3 and β −⪢ α 2 + Ti 5 Si 3 . Additionally, extrapolations in the β + α 2 + α tie-triangle observed at 1100°C indicate that two possibilities arise to represent a peritectoid reaction involving α, β and α 2 phases: β + α 2 −⪢ α and β + α −⪢ α 2 , depending on the alloy composition and on the effect of temperature on the solubility of Si in α phase.