Creep Durability of Ni-Base Single Crystal Superalloy Containing Pb Impurity

The effect of Pb on the creep properties of Ni-base single crystal superalloy was evaluated and compared with the reference data of polycrystalline superalloys. Alloy variants containing 0.04 (no Pb added), 0.9, and 31 ppm of Pb were prepared, and creep tests under different temperatures and stresses (i.e., 800/735, 900/392, 1000/245, 1100/137, and 1150 °C/137 MPa) as well as microstructural observations were conducted. The initial microstructure, such as the γ′ size and volume fraction of γ′, and the γ/γ′ microstructure after the creep test, such as the extent of raft structure formation, were almost identical in all the alloy variants. Moreover, the extent of topologically close-packed or precipitate phase formation could not be correlated with the Pb content. Based on these results and those of the creep tests, it was concluded that Pb did not affect the creep rupture life. In single crystal superalloy, no grain boundary exists, and the results of the field-emission electron-probe microanalysis indicated that Pb was dispersed in the substrate and its segregation did not occur during the creep test. Thus, in contrast to the Ni-base polycrystalline superalloy, no negative effect of Pb on the creep properties of the Ni-base single crystal superalloy was detected.