How are superalloys made

Single crystalline superalloys

Monocrystalline superalloys are metallic materials that have to withstand mechanical loads under extreme conditions of temperature (above 1000 ° C) and corrosion (fuel gases in a gas turbine). They are used as blade materials for gas turbines for aircraft engines and for power plants. There is currently no other class of material that could replace single-crystal Ni-based superalloys. Monocrystalline superalloys are produced monocrystalline using a special casting process, the Bridgman process, in vacuum investment casting. This avoids grain boundaries, which are disadvantageous in high-temperature use. After solidification, a very carefully monitored heat treatment takes place, which leads to the creation of what is probably the most famous microstructure in materials science, the γ / γ 'microstructure. This consists of small γ 'cubes (ordered intermetallic L12 phase, about 80 percent by volume, typical edge length: 0.5 µm) that are separated by narrow γ channels (cubic face-centered lattice, about 20 percent by volume, typical channel width: 0.1 µm ). In modern single crystal technology, all specialist knowledge of materials science and technology is required. You have to master the production of single crystals. It is about a targeted setting of optimal microstructures. At the same time, protective layers have to be applied, which are intended to both improve the resistance to high-temperature corrosion and also have to act as thermal insulation layers. It is about alloy development in an environment in which strategically important alloy elements are becoming scarcer. And you have to ensure good creep and fatigue resistance. To do this, complex mechanical experiments must be carried out at high temperatures (creep and fatigue tests). Of particular importance is the understanding of the elementary processes that determine the structure formation processes in production and the microstructural processes in the use of materials. This is why microscopic examination methods (scanning and transmission electron microscopy) are of particular importance. A large number of projects are being carried out at the Institute for Materials on monocrystalline Ni-based superalloys. In addition to developing new alloys, this also involves repairing turbine blades that you want to use safely for as long as possible. Last but not least, it is also important to be able to predict the mechanical behavior of single-crystal superalloys using suitable modeling methods. The Institute for Materials is currently the center of the SFB / TR 103 (From the atom to the turbine blade - Scientific basis for a new single crystal technology) funded by the German Research Foundation, in which many projects are concerned with modern single crystal technology. Those students who deal with single crystal technology often find good job and career opportunities at gas turbine manufacturers at home and abroad.
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