Investigation of equilibrium and phase stability in the liquid solid state in nickel based wrought superalloys

Isothermal holding experiments between the liquidus temperatures, T_L, and the solidus temperatures, T_S, were carried out on nickel-based wrought superalloys. It was found that during solidification the elements aluminium, cobalt and tungsten tend to dissolve in the γ matrix whereas titanium, tantalum and molybdenum tend to segregate into the liquid. Molybdenum and titanium cause the formation of brittle σ and η phases, respectively, after prolonged holding at elevated temperatures, in accordance with the results of New-PHACOMP (new phase computation).