Abstract
The present study investigates the microstructure, high-temperature creep rupture properties and oxidation resistance of three fourth-generation single-crystal Ni-based superalloys containing 0, 3.5 and 7 wt% of Ru. The addition of Ru changes the partitioning behavior of the alloying elements, decreases γ' size and increases the γ/γ' lattice misfit. The creep resistance keeps increasing as Ru content rises up 7 wt% under 1100 °C/140 MPa. However, it was discovered that 7 wt% Ru alloy has inferior creep resistance compared with the 3.5 wt% Ru one under 1150 °C/140 MPa, although no TCP precipitation was observed in this 7 wt% Ru-containing alloy. It was revealed that 7 wt% Ru-addition caused significant γ' dissolution and induced the generation of creep cavities, which may account for the anomaly. Furthermore, the increase in Ru content up to 7 wt% keeps degrading the oxidation resistance of the superalloys by facilitating the formation of pores and cracks within the oxide scales, which also accelerate scale spallation. This work suggests that excess Ru addition may adversely affect both the mechanical properties and the oxidation resistance of the fourth-generation Ni-based superalloys.
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