The Re (Ru)-rich δ-phase in Ru-containing superalloys

The formation of the hexagonal δ-phase has been investigated in Ru-containing Ni-base superalloys with Re additions in the range of 1.3–2.5 at.% (3.8–7.2 wt.%). The phase is a Re-rich solid solution with Ru partially substituting for Re. The δ-phase existed in both Ru-free and Ru-containing quaternary and multicomponent superalloys in either as-cast or heat-treated conditions. Electrochemical extraction revealed faceted, plate-shaped precipitates following aging, which were preferentially located in the dendritic regions. High levels of (Al+Ta) and Re additions enhanced δ-phase precipitation in Ru-containing superalloys. Increased levels of Ru reduce the partitioning of the Re to the δ-phase significantly. Lattice parameters of the δ-phase and the orientation relationship between δ- and γ′-phases are also reported.