Abstract:Solidification sequence of a typical Ni3Al base superalloy IC6 was studied by isothermal solidification method. The results show that the liquidus, solidus, melting point of the boride and secondaryγ′precipitation temperature of the IC6 alloy are notably higher than those of conventional nickel base superalloys because of its higher Mo content. There is no eutecticγ′precipitation during the solidification of the alloy, but a kind of Mo-richδ-Ni0.76Mo1.24primary phase precipitates together withγphase by eutectic reactionL′→δ+γ+L″in the temperature range of 1 573~1 553 K, thisδ- Ni0.76Mo1.24phase has a primitive orthorhombic structure witha=0.917 8 nm,b=0.914 2 nm andc=0.882 8 nm. Moreover, Al element of the alloy segregates in dendritic areas during isothermal solidification process, which causes secondaryγ′phase precipitate in the order of precedence from dendrites to interdendrites.

Key words: Ni3Al base superalloys; solidification process; microstructures;δ-Ni0.76Mo1.24phase