Effects of platinum group metals addition on the precipitation of topologically close-packed phase in Ni-base single crystal superalloys

• In situ TEM was applied to study the TCP suppression effects by PGMs addition.
• Pt, Ir and Ru additions all suppress TCP precipitation in a sequence of Ru >Ir> Pt.
• Ru suppresses TCP precipitation mainly by retarding its nucleation rate.
• Pt and Ir suppress TCP precipitation mainly by reducing its growth rate.
• PGMs segregate differently in TCP precipitates and affect the partition of Cr.

Precipitation of topologically close-packed (TCP) phase in Ni-base single crystal superalloys with additions of platinum group metals (PGMs) was investigated by in situ transmission electron microscopy (TEM). Pt, Ir and Ru additions are all helpful to suppress the precipitation of TCP phase, among which Ru has the largest efficiency while Pt has the least one. Comparing with the TCP precipitation in non-PGMs alloys, addition of Ru mainly retards the nucleation rate of TCP phase, but Pt and Ir mainly reduces the growth rate of TCP precipitates. Elemental partitioning investigation reveals that Pt and Ir prefer partitioning to the surrounding γ matrix rather than in the precipitated μ phase, and Ru distributes homogenously in both γ matrix and μ phase. Cr distribution in precipitated μ phase is higher in Pt/Ir-containing alloys than in Ru-containing alloy, which is supposed to be related to the different metallic bonding energy of Cr–Pt, Cr–Ir and Cr–Ru.