The Effect of Secondary Gamma-Prime on the Primary Creep Behavior of Single-Crystal Nickel-Base Superalloys

Abstract

Some second-, third-, and fourth-generation single-crystal Ni-base superalloys (i.e., Re-containing alloys) have demonstrated the propensity for excessive primary creep at intermediate temperatures. This behavior has been attributed to the presence of secondary gamma-prime precipitates in the gamma channels as well as on the Re content of the alloys. This investigation examined creep behavior for a common first-generation alloy, PWA 1480, a common second-generation alloy, PWA 1484, as well as a modified first-generation alloy, PWA 1480, with 3 wt pct rhenium added. In addition, two different aging heat treatments were given to each alloy to either precipitate or prevent the formation of fine (nanometer-scale) secondary gamma-prime in the gamma channels. The intermediate creep properties and tensile properties of the alloys were determined for both conditions. The microstructures of these samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD), and then the role of the fine-scale microstructure and the alloy composition on the primary creep deformation was determined.

Atom probe tomography of secondary γ′ precipitation in a single crystal Ni-based superalloy after isothermal aging at 1100°C

“…Furthermore, even a multimodal size distribution of c 0 precipitates (including tertiary c 0 ) may occur in some cases of polycrystalline superalloys [16]. Recently, different populations of c 0 precipitation in a commercial polycrystalline Ni-based superalloy René 88 DT (processed through powder metallurgy and used in turbine disks) has been systematically investigated by means of APT [15][16][17]24,25] [26]. In this work, the secondary c 0 precipitation via isothermal aging at 1100°C was investigated by APT.…”

Influence of Crystallographic Orientation on Creep Behavior of Aluminized Ni‐Base Single Crystal Superalloys

“…The TCP precipitates are found both in the aluminized CMSX-4 and TMS-75 superalloys since both superalloys have 3 and 5 % Re content. On the other hand, the TCP phase could not be observed in the aluminized PWA 1480 superalloy due to likely free of Re containing as reported [17].…”

Influence of Crystallographic Orientation on Creep Behavior of Aluminized Ni-base Single Crystal Superalloys

“…The TCP precipitates are found both in the aluminized CMSX-4 and TMS-75 superalloys since both superalloys have 3 and 5 % Re content. On the other hand, the TCP phase could not be observed in the aluminized PWA 1480 superalloy due to likely free of Re containing as reported [17]. The precipitation of TCPs at high temperatures is mostly associated with the formation of voids which may potentially act as initiation sites for fracture [18].…”