VHCF damage in duplex stainless steel revealed by microbeam energy-dispersive X-ray Laue diffraction

• Published in: International journal of fatigue Vol. 151; p. 106358
• Main Authors: Abboud, Ali, AlHassan, Ali, Dönges, Benjamin, Micha, Jean Sebastian, Hartmann, Robert, Strüder, Luthar, Christ, Hans-Jürgen, Pietsch, Ullrich
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.10.2021; Elsevier BV
• Subjects: Austenite; Austenitic stainless steels; Crack propagation; Damage assessment; Dispersion; Duplex stainless steel; Duplex stainless steels; Edge dislocations; Energy dispersive Laue diffraction; Energy spectra; Fatigue crack nucleation; Fatigue cracks; Fatigue failure; Ferrite; Ferritic stainless steels; Grain boundaries; High cycle fatigue; Materials fatigue; Metal fatigue; Microbeams; Microstructure; pnCCD; Stainless steel; Very high cycle fatigue; Fatigue crack nucleation; Energy dispersive Laue diffraction; Very high cycle fatigue; Duplex stainless steel; pnCCD
• ISSN: 0142-1123; 1879-3452
• DOI: 10.1016/j.ijfatigue.2021.106358

•Energy-dispersive X-ray Laue diffraction measures 3D resolved microstructure quantities making it relevant to understand the underlying interaction mechanism between dislocation and grain boundary, such as deviatoric hydrostatic strains, and the orientation and density of the so-called geometrically-necessary dislocations.•The method enables a better understanding of fatigue mechanisms and material laws, which brings us closer to the future of material science: grain boundary engineering.•X-ray scanning with a micrometer sized beam in combination with the use of an energy-dispersive 2D detector (pnCCD) provides a powerful tool to complement electron microscopy techniques in the investigation of microstructural fatigue phenomena. Microstructure of austenitic-ferritic duplex stainless steel loaded in the Very High Cycle Fatigue regime was investigated using microbeam energy-dispersive X-ray Laue diffraction. Scanning electron microscopy analysis of the surface shows that damage in the form of fatigue cracks is initiated at grain boundaries assisted by slip bands observed in austenite grains. Energy-dispersive X-ray Laue diffraction was then used to scan a damaged area containing both a fatigue crack and slip bands, in order to measure the changes in microstructure. Results from the X-ray data from the austenite grain indicates slip activation of the most favored slip system tilted by 45° with respect to the external loading direction, dividing the grain into two regions on either side of the slip band. In the ferrite phase, in front of the crack, variations in the angle and energy spectra of the diffraction peaks indicate the presence of lattice curvature and a strain gradient. In regions around the crack, diffraction peaks spatially split into several sub-peaks indicating the presence of fine granular areas separated by polarized dislocation walls. Possible reasons for the observed structural evolution are discussed and the advantages of using energy-dispersive X-ray Laue diffraction in fatigue damage analysis are illustrated.