Untersuchung der Auswirkung von sehr hohen Lastspielzahlen auf einen austenitisch-ferritischen Duplexstahl mittels in-situ Röntgendiffraktion an der Strahllinie BL10 an der Synchrotronstrahlungsquelle DELTA

The behavior of an austenitic-ferritic duplex stainless steel during very high cycle fatigue is investigated in this thesis. For this flat samples were fatigued with different load amplitudes up to 10 million cycles with an ultrasonic testing device. After that X-ray diffraction scans were performed. These measurements were done at the beamline BL10 at the synchrotron light source DELTA. Because of the grain structure of the duplex stainless steel it is possible to perform a single grain analysis. Each grain, whose lattice planes have the right orientation to the incoming X-ray beam and the detector, gives a single Bragg reflection on the detector. Different grains have different orientations and so the reflections are arranged on Debye-Scherrer-Rings. These reflections can be indexed as austenite or ferrite reflections. The rocking curves for a single grain are compared to each other after different fatigue steps. The changes in position, full width at half maximum (FWHM), intensity and integrated intensity are discussed. This reveals that not only austenite grains are affected by fatigue but also ferrite grains are. However for ferrite the changes are normally much smaller than for austenite grains. The rocking curves of the austenite grains show all possible changes and even combinations of them. Austenite grains, which are affected by fatigue, change for example their FWHM because of the formation of slip bands or formation of small angle grain boundaries due to a rotation of lattice planes. The rocking curves can not only broaden, they can even split. Changes do not only occur shortly before failiure of the sample. They already appear after 10 million load cycles with relatively small load amplitudes. Some rocking curves change first, then stay constant for a while (different loading steps) and then change again. This behavior is interpreted as the softening-hardening-softening behavior of austenite. These findings are compared with the results of the project in SPP1466.
Before the measurements could be performed, the construction of beamline BL10 at DELTA had to be finished. In this thesis, the setup of BL10 and the single components are described. The programs for controlling the vacuum system and the personal saftey system are shown. The beamline BL10 is designed for X-ray diffraction measurements and X-ray spectroscopy measurements.