Materials for sustainable turbine engine development
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Materials for sustainable turbine engine development Doug Konitzer, Steve Duclos, and Todd Rockstroh Turbine engine performance, as measured by specific fuel consumption (defined as fuel consumed relative to the thrust produced by the engine), is a key criterion in engine selection. To achieve the specific fuel consumption required of modern engines, engineers combine advanced designs and materials to achieve higher operating temperatures and, therefore, higher engine efficiency. One of the difficulties of using advanced materials is that they exploit scarce, hard-to-replace elements to allow higher operating temperatures. In this article, we describe steps being taken by General Electric Co. and the turbine engine industry to continue to improve engines in a material space constrained by material availability. As a specific example, we focus on the transition metal rhenium.
Introduction In their drive to increase engine efficiency, materials engineers have developed a wide range of materials. Whereas early engines were made from steel and exhibited relatively simple geometries, today’s engines incorporate many different materials and complex geometries depending on the needs of each specific component. Materials such as polymer-matrix composites, titanium alloys, wrought nickel and cobalt superalloys, and both equiaxed and single-crystal cast superalloys have all found applications in engines. In addition, each of these new material classifications has a range of associated compositions. For example, cast single-crystal nickel-based superalloys are classified into generations depending on the amount of rhenium in the specific alloys. Whereas rhenium is not present in firstgeneration single-crystal superalloys, it is used in increasing quantities in the second- and third-generation single-crystal superalloys. To continue to improve engine efficiency, it will be necessary to develop even more advanced materials for high-temperature use. In general, the advanced materials being developed are more complex and contain elements that are scarcer than was the case for previous generations of materials. The challenge of sustainability was addressed at the International Congress on Sustainability Science & Engineering forum in 2009, for which the overview stated: “Sustainability has become a common currency in describing proactive plans and solutions in many scientific, engineering, and social science
disciplines with no consensus on what sustainability means.”1 To some extent, this remains true today, as the general definition of sustainable development (see the introductory article in this issue by Green et al.) is of limited use in assessing the sustainability of a given part or product. For the purposes of this article, we focus on a more specialized aspect of sustainability that strongly affects current and future aviation technology: conserving elements that are critical to producing components that enable efficiency improvements in turbine engines. In this case, the focus on sustainability arises because of the business desire
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