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7185 |
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Thursday, June 23, 2022, Saal Brüssel 9:20 AM Quality assurance, process and product quality |
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Sample geometry for the investigation of wetting and flow behavior of brazing material in the gap during high-temperature brazing |
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Jane Awayes* / TU-Berlin / Siemens Energy, Germany Ingo Reinkensmeier / Siemens Energy, Germany Claudia Fleck/ Technische Universität Berlin, Germany Emily Thannhaeuser/ Siemens Energy, Germany |
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In times of renewable energy transition, large stationary gas turbines still play an important role around peak loads. Due to increasingly stringent limits on CO2 and NOx emissions in stationary gas turbines, the iteration cycles in the development of turbine components, including gas turbine blades and burners, are becoming shorter and shorter. These components or attachments (in the burner) are primarily manufactured using vacuum investment casting. The production of these components, which are exposed to high temperatures, is time-consuming and cost-intensive. Due to the high inlet temperatures in the turbine area, which are at the limit of the melting temperatures of the blade and vane materials, technologically challenging cooling concepts must be implemented here. The manufacture of components including concepts are either very time-critical in investment casting or technologically not feasible at all. Therefore, a shift from the casting process to the Laser Powder Bed Fusion (LPBF) manufacturing process can shorten delivery times and the development period to test new developments at short notice. In addition to the time-saving advantage, LPBF offers extended geometric flexibility. However, the limitations of the LPBF method are currently still the limitation of component size by the installation chamber dimensions. Both for cost reasons and size limitations, modular construction is considered from the outset in the design phase. Due to the complexity of manufacturing nickel-base superalloys by LPBF, a subsequent welding process for joining the modular components to form an assembly is usually not performed. Mainly due to the formation of cracks during the local heat input. High-temperature brazing on the other hand, is of particular importance here to generate an innovative turbine component from the individual modules that meets the requirements of the renewable energy transition. Preliminary investigations revealed an altered diffusion behavior on LPBF materials compared to conventional, cast materials. Wetting and filling of the brazing gap was shown to be significantly different for LPBF versus cast material. The purpose of this paper is to contribute to the parameter selection for high temperature brazing. For this aim, a novel sample geometry was developed, which investigates the influence of gap filling, wetting and flow behavior of brazing material on LPBF base materials. Haynes 282 is as an important base material for the turbine industry. In this context, the brazing parameters, and the necessary surface preparation with two commonly used brazing systems Ni660 and Ni620 are presented. The flow path of the brazing material in the gap was documented and analyzed by Micro-CT, and diffusion depths were evaluated by SEM and optical microscopy. This work on understanding the wettability of LPBF alloys provides the basis for joining gas turbine components in modular design. |