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

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.