a bUnderstanding of the solution heat treatment response of a second generation, single-crystal nickel-based superalloy, CMSX-4, is necessary before the process can be shortened in an effort to save money. The current solution heat treatment used for CMSX-4 involves high temperatures for long durations and can be quite expensive. This investigation helps to characterize the heat-treatment process for this alloy. The achieved microstructure is described for both the as-cast and fully solution-annealed conditions. In addition, an alternate, less expensive heat treatment was selected for its lower temperatures and shorter overall duration. Microstructures and differential thermal analysis are presented for all three conditions.

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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.

Primary creep occurring at intermediate temperatures (650°C to 850°C) and loads greater than 500 MPa has been shown to result in significant primary creep strain (often exceeding 5-10%) during the first few hours of a creep test. This investigation examines how rhenium additions and aging heat treatment affect the primary creep behavior of PWA

Research SummaryHigh-Temperature alloys How would you… …describe the overall signifi cance of this paper?Understanding how materials deform at high temperatures will allow for the development of materials that add strength and can be used at higher temperatures.…describe this work to a materials science and engineering professional with no experience in your technical specialty?This paper examines the effects of composition and processing on the creep properties of single-crystal nickel-based superalloys. …describe this work to a layperson?Higher effi ciencies and lower emissions in gas turbines require continued material development. This work is intended to identify ways to fi nd higher-temperaturecapable materials and/or alloys.