TY - JOUR A1 - Richter, Tim A1 - Erxleben, Kjell A1 - Rhode, Michael A1 - Schröpfer, Dirk A1 - Michael, Thomas A1 - Börner, Andreas T1 - Microstructure characterization of dissimilar metal welds of innovative high- and medium-entropy alloys to austenitic stainless steels joint by tungsten inert gas and friction stir welding JF - Welding in the World N2 - The new multi-element alloying concept of systems with defined entropy (HEA — high-entropy alloy or MEA — medium-entropy alloy) is increasing in material research interest. Improved properties or combinations of properties are shown by several systems. Thus, the resulting microstructures and production of HEA/MEA as well as properties have been primarily investigated so far. Furthermore, processing is a key issue to transfer HEA/MEA systems to real components. Since welding is the most important joining process for metals, it is crucial to investigate the influence of welding to guarantee component integrity. Since most HEA are made of expensive alloying elements such as Co or Ni, they will not be used entirely as structural materials. Thus, it can be advantageous to weld conventional alloys such as austenitic stainless steels with the HEA and MEA to produce components that are both application-oriented and economically viable. Therefore, in this paper, first results of dissimilar metal welding, by tungsten inert gas (TIG) and friction stir welding (FSW), of a CoCrFeMnNi HEA as well as a CoCrNi MEA with a conventional AISI 304 austenitic stainless steel are presented. The focus is on the microstructure formation due to the two welding processes. The results of TIG welding show a dendritic microstructure, whereas in FSW both materials are stirred but still coexist. KW - Metals and Alloys KW - Mechanical Engineering KW - Mechanics of Materials PY - 2023 DO - https://doi.org/10.1007/s40194-023-01618-z SN - 1878-6669 SP - 1 EP - 9 PB - Springer AN - OPUS4-59252 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rhode, Michael A1 - Kromm, Arne A1 - Mente, Tobias A1 - Brackrock, Daniel A1 - Czeskleba, Denis A1 - Kannengießer, Thomas T1 - Component test for the assessment of delayed hydrogen-assisted cracking in thick-walled SAW joints for offshore applications JF - Welding in the World N2 - Offshore wind turbines continuously increase in size and weight and demand adequate offshore foundations concepts like monopiles, tripods, or jackets. These components are typically constructed using submerged arc welding (SAW) with high-strength thick steel plates like the S420ML. During welding, the occurrence of delayed hydrogen-assisted cracking (HAC) must be anticipated. HAC is a critical combination of the local hydrogen concentration within a susceptible microstructure under certain mechanical load, i.e., the occurring (welding) residual stresses. The welding sequence of the thick-walled plates complicates the residual stress distribution due to the necessary repeated thermal cycling, i.e., welding seam/layer deposition to fill the joint. For that purpose, SAW with two-wire-technique was used to weld a specially designed and prototype-like mock-up of a real component with a thickness of 50 mm, filled with over 20 passes and a seam length of 1000 mm. Additional welded stiffeners simulated the effect of a high restraint, to achieve critical HAC conditions. The necessity of a minimum waiting time (MWT) before the NDT can be conducted (to exclude HAC) was critically verified by the application of ultrasonic testing of the welded joint at different time-steps of the NDT of up to 48 h after the completion welding. The residual stresses were determined by a robot XRD goniometer. Tensile residual stresses up to the yield limit are found both in the weld metal and in the heat-affected zone. Numerical modeling allowed the qualitative estimation of the hydrogen diffusion in the weld. No noticeable HAC occurrence was identified and confirms the high cracking resistance of the investigated material. Finally, the applicability of the MWT concept should be critically discussed. KW - Hydrogen KW - Cold cracking KW - Minimum Waiting Time KW - Offshore steel grade KW - Component test PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-591981 DO - https://doi.org/10.1007/s40194-023-01658-5 SP - 1 EP - 15 PB - Springer Science and Business Media LLC AN - OPUS4-59198 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schubnell, J. A1 - Konidena, S. K. A1 - Jung, M. A1 - Braun, M. A1 - Ehlers, S. A1 - Madia, Mauro A1 - Kannengießer, Thomas A1 - Löschner, D. T1 - Approach for the probabilistic fatigue assessment of welded joints based on the local geometry of the weld seam JF - Fatigue and Fracture Engineering Materials and Structures N2 - Welded joints show large variation of the weld toe geometry along the weld seam, which is one important reason for the comparably large scatter in fatigue life. Therefore, it is crucial to take the local geometry at the weld toe into account, to reduce the conservatism in fatigue assessment of welded joints. This study is based on the IBESS procedure for the calculation of the fatigue strength, whereby the evaluation of local geometrical parameters is carried out by means of 3D surface scans. The approach is validated against 26 fatigue test series. The fatigue life is in general overpredicted, whereas good agreement is achieved for high stress ratio (R = 0.5). A sensitivity analysis conducted with IBESS shows that weld toe radii ρ < 2 mm and flank angle α < 30° have a significant influence on the calculated fatigue strength. In contrast to this, no strong correlation between ρ and the fatigue strength was determined experimentally in this study. KW - 3D Scanning KW - Fatigue Strength KW - Fracture Mechanics KW - IBESS Approach KW - Local Weld Geometry KW - Welded Joints PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-585700 DO - https://doi.org/10.1111/ffe.14170 SN - 8756-758X SP - 1 EP - 20 PB - Wiley AN - OPUS4-58570 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Han, Ying A1 - Kruse, Julius A1 - Rosalie, Julian A1 - Radners, J. A1 - von Hartrott, P. A1 - Skrotzki, Birgit T1 - Influence of mean stress and overaging on fatigue life of aluminum alloy EN AW-2618A JF - Materials Science & Engineering A N2 - Fatigue tests were performed on the forged aluminum alloy EN AW-2618A in the T61 state. Different stress ratios (R = -1, R = 0.1) were selected to study the influence of mean stress on fatigue life. Two overaged states (10 h/230 ◦C, 1000 h/230 ◦C) were also tested to investigate the influence of overaging on fatigue life. Transmission electron microscopy (TEM) was used to characterize the precipitates (S-phase), which are mainly responsible for the strength of the alloy. A fractographic analysis was also performed to determine the failure mode. Overaging reduces the fatigue life compared to the T61 state. The longer the aging time, the lower the fatigue resistance. The reason is the decrease in (yield) strength, which correlates with the radius of the S-phase: the precipitate radius increases by a factor of approximately two for the overaged states compared to the initial state. The analysis of the fracture surfaces showed crack initiation occurs predominantly on the outer surface and is associated with the primary phases. KW - Aluminum alloys KW - Aging KW - Fatigue KW - Microstructure KW - Electron microscopy KW - S-Phase PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-583708 DO - https://doi.org/10.1016/j.msea.2023.145660 SN - 0921-5093 VL - 886 SP - 1 EP - 10 PB - Elsevier B.V. AN - OPUS4-58370 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Vecchiato, L. A1 - Madia, Mauro A1 - Meneghetti, G. T1 - Extension of the peak stress method to estimate the fatigue limit of welded joints by means of the cyclic R-curve method JF - Theoretical and applied fracture mechanics N2 - A new simplified and effective method has been formalised to estimate the Constant Amplitude Fatigue Limit (CAFL) of stress-relieved steel welded joints subjected to uniaxial push–pull loading and failing from the weld toe. Starting from the sharp V-notch assumption of the NSIF approach and the cyclic R-curve of the material in the heat affected zone, the proposed method identifies the CAFL as threshold level of the local stress field at the V-notched weld toe in the uncracked configuration. Such threshold stress field assures the crack arrest at the V-notched weld toe, according to the cyclic R-curve analysis. The method has been validated against experimental results and proved effective for a straightforward assessment of the CAFL of welded joints, as the stable crack propagation analysis of classical fracture mechanics approaches can be avoided. KW - Cyclic R-curve KW - Welded joint KW - Fatigue limit KW - Peak stress method KW - Finite element analysis PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-581059 DO - https://doi.org/10.1016/j.tafmec.2023.104039 SN - 0167-8442 VL - 127 SP - 1 EP - 19 PB - Elsevier AN - OPUS4-58105 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schröder, Nina A1 - Rhode, Michael A1 - Kannengießer, Thomas T1 - Thermodynamic prediction of precipitations behaviour in HAZ of a gas metal arc welded S690QL with varying Ti and Nb content JF - Welding in the World, The International Journal of Materials Joining N2 - For a significant increase in the strength of high-strength fine-grained structural steels with a nominal yield strength ≥690 MPa, the addition of microalloying elements such as Nb and Ti is required. The standard specifications for the chemical composition of these steels (e.g., in EN 10025-6) often only give the manufacturer limit contents to achieve the defined properties. The effect of the alloying elements in the heat affected zone (HAZ) is sometimes completely contrary. This makes it difficult to adequately predict the batch dependency regarding weldability and the load-bearing behaviour of the welded joint. Three different micro-alloyed steels of the grade S690QL were produced on a laboratory scale, focusing on different Nb and Ti contents. To investigate the tempering effect, these were gas metal arc welded in three layers. In addition to metallographic investigations of individual HAZ areas, thermodynamic phase calculations were carried out using Thermo-Calc, following variations in the chemical composition. This provides an understanding of phase transformation, precipitation growth, and dissolution during welding as a function of temperature and cooling conditions. The results show a divergent metallurgical behaviour in the HAZ of the three different micro-alloyed steels. Thereby, the Ti micro-alloyed grade showed a strong softening of the HAZ in contrast to the Nb micro-alloyed grade. This can be attributed to a contrary precipitation behaviour during welding. KW - High-strength structural steel KW - Gas metal arc welding KW - HAZ-softening KW - Microalloying influences KW - Thermodynamic simulation PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-579988 DO - https://doi.org/10.1007/s40194-023-01550-2 SN - 0043-2288 SP - 1 EP - 10 PB - Springer AN - OPUS4-57998 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bergant, M. A1 - Larrosa, N. A1 - Yawny, A. A1 - Madia, Mauro T1 - Short crack growth model for the evaluation of the fatigue strength of WAAM Ti-6Al-4V alloy containing pore-type defects JF - Engineering Fracture Mechanics N2 - The role of defects in the fatigue strength of Wire Arc Additively Manufactured (WAAMed) Ti-6Al-4V is analysed by means of the IBESS model, a fracture mechanics short crack growth approach based on the cyclic R-curve. Pores and crack-like defects are analysed. Estimations of the role of pore shape and size agree well with published fatigue data of WAAM Ti-6Al-4V with pores. The model is also used to explain the effect of fabrication defects on the scatter of experimental data. This demonstrates that short crack growth models represent a suitable engineering tool for the fatigue assessment of defective AM materials. KW - WAAM Ti-6Al-4V KW - Cyclic R-curve KW - IBESS model for short cracks KW - Kitagawa-Takahashi (K-T) diagram PY - 2023 DO - https://doi.org/10.1016/j.engfracmech.2023.109467 SN - 0013-7944 VL - 289 SP - 1 EP - 21 PB - Elsevier Ltd. AN - OPUS4-57963 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schröder, Jakob A1 - Evans, Alexander A1 - Luzin, V. A1 - Abreu Faria, G. A1 - Degener, Sebastian A1 - Polatidis, E. A1 - Čapek, J. A1 - Kromm, Arne A1 - Dovzhenko, G. A1 - Bruno, Giovanni T1 - Texture-based residual stress analysis of laser powder bed fused Inconel 718 parts JF - Journal of Applied Crystallography N2 - Although layer-based additive manufacturing methods such as laser powder bed fusion (PBF-LB) offer an immense geometrical freedom in design, they are typically subject to a build-up of internal stress (i.e. thermal stress) during manufacturing. As a consequence, significant residual stress (RS) is retained in the final part as a footprint of these internal stresses. Furthermore, localized melting and solidification inherently induce columnar-type grain growth accompanied by crystallographic texture. Although diffraction-based methods are commonly used to determine the RS distribution in PBF-LB parts, such features pose metrological challenges in their application. In theory, preferred grain orientation invalidates the hypothesis of isotropic material behavior underlying the common methods to determine RS. In this work, more refined methods are employed to determine RS in PBF-LB/M/IN718 prisms, based on crystallographic texture data. In fact, the employment of direction-dependent elastic constants (i.e. stress factors) for the calculation of RS results in insignificant differences from conventional approaches based on the hypothesis of isotropic mechanical properties. It can be concluded that this result is directly linked to the fact that the {311} lattice planes typically used for RS analysis in nickel-based alloys have high multiplicity and less strong texture intensities compared with other lattice planes. It is also found that the length of the laser scan vectors determines the surface RS distribution in prisms prior to their removal from the baseplate. On removal from the baseplate the surface RS considerably relaxes and/or redistributes; a combination of the geometry and the scanning strategy dictates the sub-surface RS distribution. KW - Additive manufacturing KW - Electron backscattered diffraction KW - Principal stress KW - Residual stress PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-578331 DO - https://doi.org/10.1107/S1600576723004855 SN - 1600-5767 VL - 56 IS - Pt 4 SP - 1076 EP - 1090 AN - OPUS4-57833 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Roveda, Ilaria A1 - Serrano Munoz, Itziar A1 - Haubrich, J. A1 - Requena, G. A1 - Madia, Mauro T1 - Influence of post-process heat treatments on the fatigue crack propagation behaviour of a PBF-LB/M AlSi10Mg alloy JF - International Journal of Fatigue N2 - The microstructure has a great influence on short fatigue crack growth in metallic materials. Laser-based Powder Bed Fusion AlSi10Mg alloys exhibit in the as-built condition a fine fibrous Si structure and a supersaturated solid solution of Si in the α-Al matrix, which is significantly modified by heat treatments starting already at temperatures under 260 °C. This study focuses on the influence of post-process heat treatments on the microstructural evolution and the resulting fatigue crack growth resistance. As compared to the as-built condition, two heat treatments at 265 °C/1 h and at 300 °C/2 h are found to be beneficial to the fatigue crack growth resistance of the investigated material. KW - Additive manufacturing KW - Fatigue crack growth KW - Cyclic R-curve KW - Heat treatment PY - 2023 DO - https://doi.org/10.1016/j.ijfatigue.2023.107808 SN - 0142-1123 VL - 175 SP - 1 EP - 12 PB - Elsevier Ltd. AN - OPUS4-57822 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Serrano Munoz, Itziar A1 - Pfretzschner, Beate A1 - Kromm, Arne A1 - Nadammal, Naresh A1 - Kardjilov, N. A1 - Markötter, Henning A1 - Neuwirth, T. A1 - Schulz, M. A1 - Griesche, Axel T1 - High-resolution Bragg-edge neutron radiography detects grain morphology in PBF-LB/M IN718 JF - Materialia N2 - One of the main advantages of metal additive manufacturing (MAM) techniques is their ability to produce components with site-specific microstructural features. Nevertheless, microstructural defects and lack of repeatability are still major concerns in MAM. In this study, a laser powder bed fusion (PBF-LB/M) IN718 material, produced using two different scan length vectors, is investigated using Bragg-edge neutron 2D imaging (BENI) combined with electron backscatter diffraction (EBSD) analysis. BENI is able to detect, on a macroscopic scale, process-induced changes in texture in a large field of view covering the entire sample (20×80 mm2). In addition, high-resolution BENI (HR-BENI), with a pixel size of 12.8 µm, provides a micro-scale examination of the local variations of texture and grain morphology, otherwise undistinguishable using the standard resolution. As such, HR-BENI offers a straightforward and detailed way of screening the integrity of MAM parts at cm-length scales. KW - Bragg-edge neutron 2D imaging (BENI) KW - Metal additive manufacturing (MAM) KW - IN718 PBF-LB/M KW - Crystallographic texture control KW - Electron backscatter diffraction (EBSD) PY - 2023 DO - https://doi.org/10.1016/j.mtla.2023.101827 SN - 2589-1529 VL - 30 SP - 1 EP - 6 PB - Elsevier CY - Amsterdam AN - OPUS4-57819 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -