Calculated ternary diagram of Ti-Al-Si system

The phase equilibria between beta (body centred cubic, bcc), alpha (hexagon al closed packed, hcp), Ti3Al-alpha(2)(hcp), and Ti5Si3(hcp) in the Ti-Al-S i system have been investigated in the temperature range 700-1200 degrees C . Isothermal sections of the ternary phase diagram have been assessed emplo ying thermodynamic software, which uses the compound energy model to descri be the phases mathematically. Available experimental phase equilibria resul ts on the Ti-Al-Si system were used to calculate missing binary and ternary interaction parameters and assess isothermal phase diagrams. Extrapolation s in the resulting tie triangles indicate the existence of three eutectoid reactions in the Ti rich corner of the ternary diagram: beta --> alpha + Ti 5Si3, alpha --> alpha(2) + Ti5Si3, and beta --> alpha(2) + Ti5Si3. Addition ally, extrapolations in the beta + alpha(2) + alpha tie triangle observed a t 1100 degrees C indicate that two possibilities arise to represent a perit ectoid reaction involving alpha, beta, and alpha(2) phases: beta + alpha(2) --> alpha and beta + alpha --> alpha(2), depending on the alloy compositio n and the effect of temperature on the solubitlity of Si in the alpha phase .