POLYCRYSTALLINE γ(Ni)/γ′ (Ni_3Al)-δ(Ni3Nb) EUTECTIC Ni-BASE SUPERALLOYS: CHEMISTRY, SOLIDIFICATION AND MICROSTRUCTURE

摘要

A novel type of γ/γ′-δ eutectic polycrystalline Ni-base superalloyhas been recently demonstrated to possess promising mechanicalproperties at 700～800 °C, yet much of our knowledge regardingthis eutectic alloy system is still qualitative in nature. A matrix ofalloys spanning a broad range of alloy compositions wereexamined to improve our understanding of various alloyingeffects on the solidification behavior and as-cast microstructure ofmulti-component γ/γ′-δ eutectic alloys. While the volume fractionof constituent phases was observed to be closely related with theNb concentration, it could also be effectively modified byadditions of other elements. Solidus and liquidus temperatures ofthese γ/γ′-δ alloys were also found to vary with different soluteconcentrations, with a general decrease in solidus temperature assolute content increases. Interestingly, Cr, Mo and W were foundto induce similar changes on the solidification and microstructureof this eutectic system. Extensive comparison between theseexperimental results and Computherm Pandat predictions wascarried out, which confirmed the reliability of Pandat in predictingthe qualitative trends for this eutectic system. Althoughsatisfactory agreement was found between the measured andcalculated solidus temperatures, additional phase equilibriainformation of multi-component γ/γ′-δ alloys is required toimprove the predictive capability on other properties.