Mechanisms of Topologically Close-Packed Phase Suppression in an Experimental Ruthenium-Bearing Single-Crystal Nickel-Base Superalloy at 1100 °C

摘要

Ruthenium (Ru) suppresses the precipitation of deleterious topologically close-packed (TCP) phases in high refractory content single-crystal Ni-base superalloys. The effectiveness of Ru as a TCP suppressant appears to be the net effect of its limited solubility in the TCP phase, a lower density of structural growth ledges for atomic attachment at the TCP/matrix interface, and destabilization of the γ′ phase at elevated temperatures. These characteristics combine to limit the growth rates of precipitates and decrease the driving force for TCP precipitation, which has the secondary effect of reducing the TCP nucleation rate. The reduction in γ′ volume fraction upon the addition of Ru is particularly potent due to the sensitivity of the rhenium (Re) content in the γ matrix to changes in the γ′ volume fraction.