Solidification of high-refractory ruthenium-containing superalloys

The effect of alloy chemistry on single crystal solidification has been investigated in a series of model high refractory Ni-base superalloys with variations in ruthenium, rhenium and aluminum. Over the range of composition investigated, the initial phase to form during solidification was either the gamma phase (FCC Ni-solid solution) or the delta phase (HCP Rerich phase). In a quaternary Ni-Al-Ta-Re alloy containing 1.7 at.% (5.6 wt.%) Re, delta-Re nucleated at a temperature well above the liquidus temperature of pure Ni and grew unconstrained into six-fold Re-rich dendrites. These dendrites served as potent nucleation sites for gamma grains as temperature decreased during directional solidification. Ruthenium additions in the range of 2.5similar to9.0 at.% (4.1similar to14.1 wt.%) lowered the temperature at which the 6 nucleated and eventually suppressed the formation of this phase during solidification. Ru additions also increased the liquidus temperatures of the multicomponent superalloys. The implications for the design of Ru-containing superalloys are discussed. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.