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

The phase equilibria between β(bcc), α(hcp), Ti3Al-α2(hcp) and Ti5Si3(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+Ti5Si3, α−⪢α2+Ti5Si3 and β−⪢α2+Ti5Si3. Additionally, extrapolations in the β+α2+α tie-triangle observed at 1100°C indicate that two possibilities arise to represent a peritectoid reaction involving α, β and α2 phases: β+α2−⪢α and β+α−⪢α2, depending on the alloy composition and on the effect of temperature on the solubility of Si in α phase.