New Phases in a Multicomponent High Ruthenium Single Crystal Superalloy

Abstract

Three unusual Ru-rich phases have been identified in a multicomponent Ni-base single crystal superalloy, including a L21 Ru2AlTa Heusler phase, a B2 RuAl phase and a hcp Re(Ru)-rich δ phase. These phases have their own preferential precipitation location within the dendritic structure. No conventional topologically-close-packed (TCP) phases have been observed with thermal exposure at 950oC for 1500 hours.

Formation of Secondary Reaction Zones in Diffusion Aluminide-Coated Ni-Base Single-Crystal Superalloys Containing Ruthenium

“…However, in a multicomponent system such as the superalloys studied here, it is believed that a twophase field would exist, [34] as schematically shown in Figure 11. Precipitation of b-RuAl rather than the Heusler phase [25,32] in the SRZ of the F-13 was most likely linked to the emergence of the Ni-denuded IDZ during the coating formation. The compositional shift achieved due to the loss of Ni led to the precipitation of b-RuAl in the IDZ.…”

“…The microstructural aspects and creep behavior of most of the experimental Ru alloys examined in the present study, namely, F-16, F-18, F-20, F-22, and F-30, have been previously reported. [20,21,32,35] It has been shown that the alloy F-30 exhibits a good microstructural stability and has the best creep properties among all the alloys mentioned. [21,35] For example, the minimum creep rate for the F-30 alloy at 950°C/290 MPa is approximately 10 -10 s -1 , while it is approximately an order of magnitude higher for the remaining alloys.…”

“…As expected, alloy F-13 experienced a large weight loss, because of its poor oxidation resistance. Apart from the degradation in the outer layer of the coating, large-scale precipitation of the Ru 2 AlTa-based Heusler phase [25,32] also occurred throughout the matrix of the F-16 and F-13 alloys, highlighting the unstable nature of the microstructures of these alloys. Alloy F-26 exhibited a better microstructural stability, since no such precipitation was detected, even after 100 hours of exposure at 1100°C.…”

The Effects of Co on the Microstructure and Mechanical Properties of Ni-Based Superalloys Prepared via Selective Laser Melting

“…Co can substitute Ni in the crystal lattice, and it is broadly deemed one of the main elements in γ′-strengthened Ni-based superalloys. Based on previous works, it was found that Co can cause γ′-Ni 3 (Al,Ti) to transform into γ′-(Ni,Co) 3 (Al,Ti) [ 12 , 13 , 14 ], reduce the stacking fault energy, and modify the lattice mismatch of γ/γ′ to influence the morphology of γ′ precipitates [ 15 , 16 ]. However, the effects of Co on other precipitates, such as carbides and the σ phase, have not yet been studied.…”