9.2 Versuchsanlagen und Prüftechnik
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Nickel-Iron-Alloy Modification to Enhance Additively Welded Microstructure for Subsequent Milling
(2022)
The aerospace industry uses nickel–iron alloys, e.g., FeNi36, to create moulding tools for composite materials, since these alloys have a low coefficient of thermal expansion. Nickel–iron alloys are hard-to-cut materials. The moulding tools are large in size and involve complex structures, making them cost-intensive and difficult to manufacture. Thus, the focus is set on additive manufacturing, which can additionally enable the repair of components in order to eliminate local defects. However, the process usually results in a heterogeneous microstructure and anisotropic mechanical properties. As there is a high demand for a precise and exact fit of the precision moulds and the surface quality, the welded components must be subsequently machined. Additionally, inhomogeneous microstructure may lead to unstable cutting forces and conditions. Consequently, a modification of the microstructure morphology is achieved through specific alloy modifications in order to stabilise and improve the subsequent machining process. Therefore, titanium and zirconium are chosen as modification elements with a maximum 1% weight percent and are added to nickel–iron alloy powder. The elements are alloyed, and build-up welded by plasma-transferred-arcwelding. The resulting microstructure morphology of the welded wall structure and the machining properties are then determined. It can be shown that titanium has a significant effect on the structural morphology of the welded layers, as well as on the machining.
The Oxygen Pressure Surge Test (OPST) is considered to be best practice for evaluating the burn out safety of plant components and testing the compatibility of nonmetallic materials for oxygen service. Nevertheless, there are only a few laboratories worldwide performing the OPST. The Federal Institute for Materials Research and Testing (BAM) already operates oxygen pressure surge test facilities with maximum OPST pressures of 450 bar.
However, to ensure technical innovation and to enhance research and development, the decision was made to develop a new and large-scale oxygen pressure surge test facility. Due to the size and the high potential impact energies, the test facility is located outside of Berlin at BAM Test Site for Technical Safety (TTS), where large scale testing is carried out. In addition to an intended maximum OPST pressure of 750 bar, there is the possibility of testing industrial equipment with large inner volumes and diameters. The new quick opening valve constitutes the core of the system and was developed by BAM. It allows to perform tests with the standardized pressure rise times of 15 ms to 20 ms or with adjustable pressure rise times at higher or lower values. As a result, it is possible to provide customized test parameters for specific practical applications as well as research projects.
This presentation shows the status quo of this unique test facility, its performance, its technical specifications, and its new possibilities for research and development for a long term enhancement of burn out safety in oxygen application.