TY - CONF A1 - Evans, Alexander A1 - Bruno, Giovanni A1 - Mishurova, Tatiana A1 - Serrano Munoz, Itziar A1 - Roveda, Ilaria A1 - Fritsch, Tobias A1 - Ulbricht, Alexander A1 - Sprengel, Maximilian A1 - Schröder, Jakob T1 - Residual stresses and micromechanical properties of additively manufactured metals: why do we need a paradigm shift? N2 - An overview of the challenges and successes in the methodology to characherise residual stresses and micromechnical properties in additively manufactured metals T2 - CAM2 Annual Seminar 2022 - 5-year journey CY - Gothenburg, Sweden DA - 24.10.2022 KW - Additive Manufacturing KW - Residual stress KW - AGIL KW - MANUFACT KW - Micromechnical properties PY - 2022 AN - OPUS4-56466 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Roveda, Ilaria A1 - Serrano Munoz, Itziar A1 - Kromm, Arne A1 - Madia, Mauro T1 - Investigation of residual stresses and microstructure effects on the fatigue behaviour of a L-PBF AlSi10Mg alloy N2 - Al-Si alloys produced by Laser Powder Bed Fusion (L-PBF) techniques allow the fabrication of lightweight free-shape components that find space in aerospace, automotive, biomedical and military applications. Due to the high cooling rates occurring during the building process, L-PBF AlSi10Mg alloys exhibit an ultra-fine microstructure that leads to superior mechanical properties in the as-built condition compared to conventional cast Al-Si materials. Nevertheless, L-PBF processing induces high thermal gradients, leading to deleterious residual stress levels that must be considered to avoid part distortion and unpredicted failures. In order to relax detrimental residual stress and to increase the ductility, post-processing stress relief treatments are generally performed. In as-built condition the hypoeutectic AlSi10Mg microstructure consist of fine α-Al cells containing uniformly dispersed silicon nanoparticles, which are, in addition, surrounded by a eutectic Si network. Above 260°C the silicon interconnectivity starts to breakdown into spheroidized particles and to coarsen. At the same time, the heating residual stresses are relieved. The objective of the contribution is to investigate, under different heat treatment conditions, the evolution of microstructure and residual stresses in view of optimizing the fatigue performance of the alloy. To this purpose various heat treatments in a range of temperatures between 265°C and 300°C for a duration between 15 minutes and 2 hours are performed. The microstructure modifications are analysed using a scanning electron microscope and the residual stress state is measured by laboratory X-ray diffraction. T2 - FATIGUE DESIGN 2021 CY - Online meeting DA - 17.11.2021 KW - AlSi10Mg alloy KW - Additive manufacturing KW - L-PBF KW - Residual stress KW - Heat treatment PY - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-544942 SN - 2452-3216 VL - 38 SP - 564 EP - 571 PB - Elsevier B.V. AN - OPUS4-54494 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Evans, Alexander A1 - Sprengel, Maximilian A1 - Ulbricht, Alexander A1 - Kromm, Arne A1 - Mishurova, Tatiana A1 - Serrano Munoz, Itziar A1 - Fritsch, Tobias A1 - Schröder, Jakob A1 - Kannengießer, Thomas A1 - Bruno, Giovanni T1 - Residual Stresses in Additive Manufacturing (L-PBF) N2 - Additive manufacturing (AM) technologies are experiencing an exceedingly rapid growth, driven by their potential through layer wise deposition for transformational improvements of engineering design, leading to efficiency and performance improvements. Laser Powder Bed Fusion (LPBF) is an Additive Manufacturing (AM) method which permits the fabrication of complex structures that cannot otherwise be produced via conventional subtractive manufacturing methods. Nevertheless, the rapid cooling rates associated with this process results in the formation of significant and complex residual stress (RS) fields. A large body of both experimental and simulation research has been dedicated in recent years to the control and mitigation of RS in AM. In order to validate simulations with the end goal of being able to model the residual stress state in AM components and to devise strategies for their reduction during manufacturing, experimental methods need to be able to accurately determine 3D residual stresses fields in complex geometries. Several destructive and non-destructive methods can be used to analyze the RS state, the choice of which depends on the geometry and the information required. Diffraction-based methods using penetrating neutron and synchrotron X-rays at large scale facilities offer the possibility to non-destructively spatially resolve both surface and bulk residual stresses in complex components and track their changes following applied thermal or mechanical loads. This presentation will overview the success stories of using large scale facilities by the BAM for the characterization of residual stresses in additively manufactured metallic alloys. In particular, the study of the influence of process parameters on the residual stress state and the relaxation of these stresses through heat treatment will be presented. However there remains challenges to overcome particularly of the hypotheses underlying the experimental determination of residual stresses, which will be discussed. T2 - 10th International Conference on Mechanical Stress Evaluation by Neutron and Synchrotron Radiation – MECASENS 2021 CY - Prague, Czech Republic DA - 25.11.2021 KW - Residual stress KW - Additive manufacturing KW - Diffraction KW - L-PBF KW - AGIL PY - 2021 AN - OPUS4-54105 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Evans, Alexander A1 - Sprengel, Maximilian A1 - Ulbricht, Alexander A1 - Kromm, Arne A1 - Mishurova, Tatiana A1 - Serrano Munoz, Itziar A1 - Fritsch, Tobias A1 - Schröder, Jakob A1 - Kannengießer, Thomas A1 - Bruno, Giovanni T1 - Residual Stresses in Additive Manufacturing (L-PBF) N2 - Metal Additive manufacturing (AM) technologies such as Laser Powder Bed Fusion (LPBF) enable the fabrication of complex structures, giving rise to potential improvements in component and manufacturing efficiency. However, the processes are typically characterized by the generation of high magnitude residual stress (RS) which can have detrimental consequences for subsequent applications. Therefore, the characterization of these RS fields and the understanding of their formation and mitigation through optimized processing is crucial for the wider uptake of the technology. Due to the potential complex nature and high value of components manufactured by LPBF, it is important to have suitable characterisation methods which can determine the spatial variations of RS in a non-destructive manner. Neutron diffraction is considered to be the best suited for these requirements. However, the microstructures developed in the complex thermal cycles experience in the production can pose challenges to the ND method for RS analysis. The BAM has conducted significant research over the past years to overcome these obstacles, enabling higher confidence in the RS determined in LPBF materials by neutron diffraction. This contribution will overview some of these advancements made recently at European neutron sources including on Stress-Spec at FRM2/MLZ. T2 - MLZ User Meeting 2021 CY - Online meeting DA - 07.12.2021 KW - Residual stress KW - Additive manufacturing KW - Diffraction KW - AGIL KW - Manufact PY - 2021 AN - OPUS4-54044 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Roveda, Ilaria A1 - Serrano Munoz, Itziar A1 - Kromm, Arne A1 - Madia, Mauro T1 - Investigation of residual stresses and microstructure effects on the fatigue behaviour of a L-PBF AlSi10Mg alloy N2 - Al-Si alloys produced by Laser Powder Bed Fusion (L-PBF) techniques allow the fabrication of lightweight free-shape components. Due to the high cooling rates occurring during the building process, L-PBF AlSi10Mg alloys exhibit an ultra-fine microstructure that leads to superior mechanical properties in the as-built condition compared to conventional cast Al-Si materials. Nevertheless, L-PBF processing induces high thermal gradients, leading to deleterious residual stress. In order to relax detrimental residual stress and to increase the ductility, post-processing stress relief treatments are performed. The objective of the contribution is to investigate, under different heat treatment condition, the evolution of microstructure and residual stresses in view of optimizing the fatigue performance of the alloy. To this purpose various heat treatments in a range of temperatures between 265°C and 300°C for a duration between 15 minutes and 2 hours are performed. T2 - Fatigue Design 2021 CY - Senlis, France DA - 17.11.2021 KW - AlSi10Mg KW - Additive manufacturing KW - L-PBF KW - Residual stress KW - Heat treatment PY - 2021 AN - OPUS4-53794 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ulbricht, Alexander A1 - Altenburg, Simon A1 - Mohr, Gunther A1 - Oster, Simon A1 - Sprengel, Maximilian T1 - Tales from Within: Residual Stress and Void Formation in LPBF 316L N2 - An unusual microstructure, inherent residual stresses and void formation are the three key aspects to control when assessing metallic parts made by LPBF. This talk explains an experiment to unravel the interlinked influence of the two mechanisms for the formation of residual stresses in LPBF: the temperature gradient mechanism and constricted solidification shrinkage. The impact of each mechanism on the shape and magnitudes of the residual stress distribution is described. Combined results from neutron diffraction, X-ray diffraction, computed tomography and in-situ thermography are presented. Also, influence of scan strategies as well as surface roughness of subjacent layers on void formation is shown. Results from computed tomography and in-situ thermography of a specimen dedicated to study the interaction of the melt pool with layers of powder underneath the currently illuminated surface are presented. T2 - 2nd Workshop on In-situ Monitoring and Microstructure Development in Additive Manufacturing CY - Online meeting DA - 19.04.2021 KW - Neutron diffraction KW - Laser powder bed fusion KW - In-situ thermography KW - Computed tomography KW - X-ray diffraction KW - Residual stress KW - Pore formation KW - AISI 316L PY - 2021 AN - OPUS4-52819 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Thiede, Tobias A1 - Cabeza, Sandra A1 - Mishurova, Tatiana A1 - Nadammal, Naresh A1 - Kromm, Arne A1 - Bode, Johannes A1 - Haberland, C. A1 - Bruno, Giovanni T1 - An assessment of bulk residual stress in selective laser melted Inconel 718 N2 - Additive Manufacturing (AM) of metals has become industrially viable for a large variety of applications, including aerospace, automotive and medicine. Powder bed techniques such as Selective Laser Melting (SLM) based on layer-by-layer deposition and laser melt enable numerous degrees of freedom for the geometrical design. Developing during the manufacturing process, residual stresses may limit the application of SLM parts by reducing the load bearing capacity as well as induce unwanted distortion depending on the boundary conditions specified in manufacturing. The residual stress distribution in the bulk of IN718 elongated prisms produced by SLM was studied non-destructively by means of neutron diffraction. The samples with different scanning strategies, i.e. hatching length, were measured in as-build condition (on a build plate) and after removal from the build plate. The absolute values of all stress components decreased after removal from the build plate. Together with surface scan utilizing a coordinate-measuring machine (CMM), it is possible to link the stress release to the sample distortion. Obtained results indicated different residual stress states for each of the transversal, longitudinal and normal component depending on the thermal gradient in the respective direction. T2 - ECNDT 2018 CY - Göteborg, Sweden DA - 11.06.2018 KW - Residual stress KW - Selective laser melting KW - Neutron diffraction KW - IN718 PY - 2018 UR - http://cdn.ecndt2018.com/wp-content/uploads/2018/05/ecndt-0315-2018-File001.pdf SP - 1 AN - OPUS4-45325 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bruno, Giovanni A1 - Thiede, Tobias A1 - Mishurova, Tatiana A1 - Kromm, Arne A1 - Nadammal, Naresh A1 - Bode, Johannes A1 - Cabeza, Sandra T1 - Influence of deposition hatch length on residual stress in selective laser melted Inconel 718 N2 - The present study aims to evaluate the bulk residual stresses in SLM parts by using neutron diffraction measurements performed at E3 line -BER II neutron reactor- of Helmholtz-Zentrum für Materialien und Energie (HZB) Berlin. Together with microstructure characterization and distortion measurements, it is possible to describe the stress state throughout the whole sample. The sample was measured in as-build condition (on a build plate) and after releasing from the build plate. The used material is the nickel based superalloy 718. This alloy is widely used in aerospace and chemical industries due to its superior corrosion and heat resistant properties. Obtained results indicated different residual stress states for each of the transversal, longitudinal and normal component. The normal and transversal component exhibits a rather compressive behavior while the longitudinal was tensile in the center part of the sample and became compressive towards the tip. As expected, the absolute values of all stress components decreased after releasing the sample from the building plate. A surface scan utilizing a coordinate-measuring machine (CMM) allowed us to present top surface distortion before and after releasing. The top surface showed a distortion around ±80µm after releasing. Microstructure evolution in the scanning-building cross-section is largely dominated by columnar grains. In addition, many small random orientated grains are prominent in the regions of a laser overlap during SLM. In summary, for the sample of superalloy 718 manufactured by SLM, a small distortion occurred when removing the sample from the build plate whereby the residual stress state decreases. Moreover, the observed columnar grains in the building direction could give a reason for the lowest stress values in that normal direction. However, the most important parameter controlling the residual stresses is the temperature gradient. Hence, future investigations are planned for a different scan strategy to distribute the laser impact in a more homogenous manner. T2 - WAM2018 CY - Grenoble, France DA - 09.04.2018 KW - Additive manufacturing KW - SLM KW - Residual stress KW - In718 PY - 2018 AN - OPUS4-44694 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mishurova, Tatiana A1 - Cabeza, Sandra A1 - Thiede, Tobias A1 - Nadammal, Naresh A1 - Kromm, Arne A1 - Klaus, Manuela A1 - Genzel, Christoph A1 - Haberland, Christoph A1 - Bruno, Giovanni T1 - The influence of the support structure on residual stress and distortion in SLM Inconel 718 parts N2 - The effect of support structure and of removal from the base plate on the residual stress state in selective laser melted IN718 parts was studied by means of synchrotron X-ray diffraction. The residual stresses in subsurface region of two elongated prisms in as-built condition and after removal from the base plate were determined. One sample was directly built on a base plate and another one on a support structure. Also, the distortion on the top surface due to stress release was measured by contact profilometry. High tensile residual stress values were found, with pronounced stress gradient along the hatching direction. In the sample on support, stress redistribution took place after removal from the base plate, as opposed to simple stress relaxation for the sample without support. The sample on support structure showed larger distortion compared to sample without support. We conclude that the use of a support decreases stress values but stress-relieving heat treatments are still needed. KW - Additive manufacturing KW - SLM KW - Residual stress KW - Synchrotron X-ray diffraction KW - IN718 PY - 2018 U6 - https://doi.org/10.1007/s11661-018-4653-9 SN - 1073-5623 VL - 49A IS - 7 SP - 3038 EP - 3046 PB - Springer Sciences & Business Media CY - New York, NY AN - OPUS4-45100 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hensel, J. A1 - Kromm, Arne A1 - Nitschke-Pagel, T. A1 - Dixneit, Jonny A1 - Dilger, K. T1 - Capability of martensitic low transformation temperature welding consumables for increasing the fatigue strength of high strength steel joints N2 - The use of low transformation temperature (LTT) filler materials represents a smart approach for increasing the fatigue strength of welded high strength steel structures apart from the usual procedures of post weld treatment. The main mechanism is based on the effect of the low start temperature of martensite formation on the stress already present during welding. Thus, compressive residual stress formed due to constrained volume expansion in connection with phase transformation become highly effective. Furthermore, the weld metal has a high hardness that can delay the formation of fatigue cracks but also leads to low toughness. Fundamental investigations on the weldability of an LTT filler material are presented in this work, including the characterization of the weld microstructure, its hardness, phase transformation temperature and mechanical properties. Special attention was applied to avoid imperfections in order to ensure a high weld quality for subsequent fatigue testing. Fatigue tests were conducted on the welded joints of the base materials S355J2 and S960QL using conventional filler materials as a comparison to the LTT filler. Butt joints were used with a variation in the weld type (DY-weld and V-weld). In addition, a component-like specimen (longitudinal stiffener) was investigated where the LTT filler material was applied as an additional layer. The joints were characterized with respect to residual stress, its stability during cyclic loading and microstructure. The results show that the application of LTT consumables leads to a significant increase in fatigue strength when basic design guidelines are followed. This enables a benefit from the lightweight design potential of high-strength steel grades. KW - Low transformation temperature KW - Welding KW - Fatigue strength KW - Residual stress PY - 2020 U6 - https://doi.org/10.3139/120.111562 VL - 62 IS - 9 SP - 891 EP - 899 PB - Carl Hanser Verlag AN - OPUS4-51180 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Evans, Alexander A1 - Bruno, Giovanni A1 - Sprengel, Maximilian A1 - Madia, Mauro A1 - Kromm, Arne T1 - Residual stresses in Laser Beam Melting (LBM) – Critical Review and outlook of activities at BAM N2 - Additive manufacturing (AM) technologies have experienced an exceedingly rapid growth, which is coupled with the knowledge about the resulting material properties and performance. In particular, residual stress (RS) was soon recognized as an important issue in AM parts, such that parts are usually subjected to a post build-heat-treated. Significant effort has been spent on simulations of RS in AM, especially using finite element methods. As a consequence, the experimental determination of RS has thereby become increasingly important as a validation tool for simulations, as well as a method for assessing the influence of process parameters. In particular, diffraction methods, which are fundamentally non-destructive, offer enormous possibilities to gain knowledge on the residual stress state in real components, since synchrotron radiation and neutrons can penetrate even heavy metals up to several millimeters or centimeters, respectively. Indeed, significant progress has been achieved, in the understanding of the origins of the RS fields as a function of process parameters, as well as their stability under thermal and/or mechanical exposure. In this paper, a few success stories will be outlined. It will be shown how the determination of RS in metallic parts (with the focus on those produced by laser powder bed fusion) has even revealed that process parameters that were previously considered unimportant (e.g. the position and orientation on the base plate) play a major role in the onset of residual stress accumulation. However, while RS characterization is starting to be considered in the component design, deposition strategy (e.g. build plate temperature), and even in the definition of the relevant metric to assess the quality of a part, much is still to be investigates about the hypotheses underlying its experimental determination. Therefore, some aspects to be aware of, or even those which to date are unclear, will also be discussed. These include the determination of the stress-free reference and of the principal axes of stress. All of these aspects will lead towards a comprehensive understanding of the process-structure-performance relationships in AM materials and parts. T2 - Fourth ASTM Symposium on Structural Integrity of Additive Manufactured Materials and Parts CY - Gaylord National Resort And Convention Center; National Harbor, MD DA - 07.10.2019 KW - Diffraction KW - Additive Manufacturing KW - Residual stress PY - 2019 AN - OPUS4-49367 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yu, C.-H. A1 - Peng, R. L. A1 - Luzin, V. A1 - Sprengel, Maximilian A1 - Calmunger, M. A1 - Lundgren, J.-E. A1 - Brodin, H. A1 - Kromm, Arne A1 - Moverare, J. T1 - Thin-wall effects and anisotropic deformation mechanisms of an additively manufactured Ni-based superalloy N2 - Laser powder bed fusion (LPBF) of Ni-based superalloys shows great potential for high temperature applications, for example, as a burner repair application for gas turbines where the thin-walled structure is important. It motivates this work to investigate the evolution of microstructure and the anisotropic mechanical behavior when plate-like specimens are built with a thickness from 4 mm down to 1 mm. By performing texture analysis using neutron diffraction, a clear transition in fiber texture from <011> to <001> is indicated when the specimen becomes thinner. The residual stress shows no thickness dependence, and at the subsurface the residual stress reaches the same level as the yield strength. Due to the rough as-built surface, a roughness compensation method for mechanical properties of thin-walled structures is outlined and demonstrated. Tensile tests from room temperature up to 700 ◦C have been carried out. Anisotropic mechanical behavior is found at all temperatures, which is strongly related to the anisotropic texture evolution. Stronger texture evolution and grain rotations are discovered when the tensile loading is applied along the building direction. The mechanical behavior has been compared to a wrought material, where the high dislocation density and the subgrain structure of the LPBF material result in a higher yield strength. Combining the statistical texture analysis by neutron diffraction with mechanical testing, EBSD grain orientation mapping and the investigation of dislocation structures using transmission electron microscopy, this work illustrates the significance of texture for the thin-wall effect and anisotropic mechanical behavior of LPBF materials. KW - Hastelloy X KW - Hot tensile test KW - Crystallographic texture KW - Roughness KW - Residual stress KW - Dislocation density PY - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-518759 VL - 36 SP - 101672 PB - Elsevier B.V. AN - OPUS4-51875 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ulbricht, Alexander A1 - Altenburg, Simon A1 - Sprengel, Maximilian A1 - Sommer, Konstantin A1 - Mohr, Gunther A1 - Fritsch, Tobias A1 - Mishurova, Tatiana A1 - Serrano Munoz, Itziar A1 - Evans, Alexander A1 - Hofmann, Michael A1 - Bruno, Giovanni T1 - Separation of the Formation Mechanisms of Residual Stresses in LPBF 316L N2 - Rapid cooling rates and steep temperature gradients are characteristic of additively manufactured parts and important factors for the residual stress formation. This study examined the influence of heat accumulation on the distribution of residual stress in two prisms produced by Laser Powder Bed Fusion (LPBF) of austenitic stainless steel 316L. The layers of the prisms were exposed using two different border fill scan strategies: one scanned from the centre to the perimeter and the other from the perimeter to the centre. The goal was to reveal the effect of different heat inputs on samples featuring the same solidification shrinkage. Residual stress was characterised in one plane perpendicular to the building direction at the mid height using Neutron and Lab X-ray diffraction. Thermography data obtained during the build process were analysed in order to correlate the cooling rates and apparent surface temperatures with the residual stress results. Optical microscopy and micro computed tomography were used to correlate defect populations with the residual stress distribution. The two scanning strategies led to residual stress distributions that were typical for additively manufactured components: compressive stresses in the bulk and tensile stresses at the surface. However, due to the different heat accumulation, the maximum residual stress levels differed. We concluded that solidification shrinkage plays a major role in determining the shape of the residual stress distribution, while the temperature gradient mechanism appears to determine the magnitude of peak residual stresses. T2 - MLZ User Meeting 2020 CY - Online meeting DA - 08.12.2020 KW - Computed tomography KW - Neutron diffraction KW - X-ray diffraction KW - Additive manufacturing KW - Residual stress KW - Thermography KW - LPBF KW - Laser Powder Bed Fusion PY - 2020 AN - OPUS4-51793 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Madia, Mauro A1 - Bruno, Giovanni A1 - Evans, Alexander A1 - Sprengel, Maximilian A1 - Kromm, Arne T1 - Residual stresses in Laser Beam Melting (LBM) – Critical Review and outlook of activities at BAM N2 - Additive manufacturing (AM) technologies have experienced an exceedingly rapid growth, which is coupled with the knowledge about the resulting material properties and performance. In particular, residual stress (RS) was soon recognized as an important issue in AM parts, such that parts are usually subjected to a post build-heat-treated. Significant effort has been spent on simulations of RS in AM, especially using finite element methods. As a consequence, the experimental determination of RS has thereby become increasingly important as a validation tool for simulations, as well as a method for assessing the influence of process parameters. In particular, diffraction methods, which are fundamentally non-destructive, offer enormous possibilities to gain knowledge on the residual stress state in real components, since synchrotron radiation and neutrons can penetrate even heavy metals up to several millimeters or centimeters, respectively. Indeed, significant progress has been achieved, in the understanding of the origins of the RS fields as a function of process parameters, as well as their stability under thermal and/or mechanical exposure. In this paper, a few success stories will be outlined. It will be shown how the determination of RS in metallic parts (with the focus on those produced by laser powder bed fusion) has even revealed that process parameters that were previously considered unimportant (e.g. the position and orientation on the base plate) play a major role in the onset of residual stress accumulation. However, while RS characterization is starting to be considered in the component design, deposition strategy (e.g. build plate temperature), and even in the definition of the relevant metric to assess the quality of a part, much is still to be investigates about the hypotheses underlying its experimental determination. Therefore, some aspects to be aware of, or even those which to date are unclear, will also be discussed. These include the determination of the stress-free reference and of the principal axes of stress. All of these aspects will lead towards a comprehensive understanding of the process-structure-performance relationships in AM materials and parts. T2 - Fourth ASTM Symposium on Structural Integrity of Additive Manufactured Materials and Parts CY - Gaylord National Resort And Convention Center; National Harbor, MD, USA DA - 07.10.2019 KW - Residual stress KW - Additive Manufacturing KW - Diffraction PY - 2019 AN - OPUS4-49822 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Evans, Alexander A1 - Thiede, Tobias A1 - Mishurova, Tatiana A1 - Kromm, Arne A1 - Cabeza, Sandra A1 - Serrano Munoz, Itziar A1 - Ulbricht, Alexander A1 - Sprengel, Maximilian A1 - Bruno, Giovanni T1 - Residual stresses in am review and oulook of activities at BAM N2 - Critical discussion of residual stress Analysis in additive manufacturing from examples in literature and an overview of activities at BAM T2 - Workshop on Fatigue of Additive Manufactured Metallic Components CY - BAM, Berlin, Germany DA - 16.05.2019 KW - Diffraction KW - Additive Manufacturing KW - Residual stress PY - 2019 AN - OPUS4-49843 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ulbricht, Alexander A1 - Altenburg, Simon A1 - Sprengel, Maximilian A1 - Thiede, Tobias A1 - Serrano Munoz, Itziar A1 - Mishurova, Tatiana A1 - Mohr, Gunther A1 - Evans, Alexander A1 - Bruno, Giovanni T1 - How Temperature Gradient Influences the Formation of Residual Stresses in Metallic Parts Made by L-PBF N2 - Rapid cooling rates and steep temperature gradients are characteristic of additively manufactured (AM) parts and important factors for residual stress formation which have implications on structural integrity. This study examined the influence of heat input on the distribution of residual stresses in two prisms produced by laser powder bed fusion (L-PBF) of austenitic stainless steel 316L. The layers of the prisms were exposed using two distinct helix scanning strategies: one scanned from the centre to the perimeter and the other from the perimeter to the centre. Residual stresses were characterised at one plane perpendicular to the building direction at half of its build height using neutron diffraction. In addition, the defect distribution was analysed via micro X-ray computed tomography (µCT) in a twin specimen. Both scanning strategies reveal residual stress distributions typical for AM: compressive stresses in the bulk and tensile stresses at the surface. However, temperature gradients and maximum stress levels differ due to the different heat input. Regarding the X-ray µCT results, they show an accumulation of defects at the corners where the laser direction turned through 90°. The results demonstrate that neutron diffraction and X-ray µCT can be successfully used as non-destructive methods to analyse through-thickness residual stress and defect distribution in AM parts, and in the presented case, illustrate the influence of scanning strategies. This approach contributes to deeper assessment of structural integrity of AM materials and components. T2 - First European Conference on Structural Integrity of Additively Manufactured Materials (ESIAM19) CY - Trondheim, Norwegen DA - 09.09.2019 KW - AGIL KW - Neutron diffraction KW - Thermography KW - Additive manufacturing KW - Residual stress PY - 2019 AN - OPUS4-49805 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kromm, Arne A1 - Kannengießer, Thomas T1 - Online-Observation of Martensite Formation by combined use of Synchrotron Diffraction and Dilatometry N2 - Welding residual stress engineering by means of an adjusted martensite phase transformation would be highly attractive as detrimental tensile residual stresses may be prevented already during welding without time and cost intensive post processing. The present study shows a synchrotron diffraction analysis of a martensitic steel subjected to thermo-mechanical load cycles. Experiments were conducted regarding the microstructural strain response during the austenite to martensite transformation. The strains are a function of the temperature and the specific loads applied during cooling. The relation between the transformation plasticity of the material, the amount of martensite formed and the arising strains can thus be assessed. The lattice plane specific strains were compared to experimental findings from (macro) dilatation tests. It is shown that the microscopic material behavior differs remarkably from the one observed on the macroscopic scale, what leads to characteristic residual stresses in the material. T2 - Visual-JW 2019 & WSE 2019 The 5th International Symposium on Visualization in Joining & Welding Science through Advanced Measurements and Simulation & The 8th International Conference of Welding Science and Engineering CY - Osaka, Japan DA - 21.11.2019 KW - Martensite KW - Synchrotron KW - Dilatometry KW - Residual stress KW - Phase transformation PY - 2019 SP - 83 EP - 84 PB - SEIEI Printing Co., Ltd CY - Osaka, Japan AN - OPUS4-49770 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kannengießer, Thomas A1 - Kromm, Arne A1 - Lausch, Thomas A1 - Schroepfer, Dirk A1 - Hannemann, Andreas T1 - In-situ Observation of Stress Evolution and Cracking during High Strength Steel Welding N2 - Residual stresses are crucial when assessing the performance of welded components. The present work deals with the possibilities of transferring the real-life boundary conditions of welding, which influence the residual stress, into the laboratory. The possibilities of a test system with a load capacity of 2 MN specifically developed for online monitoring of stress formation and cracking are shown. Due to the structural design, global process, geometry and material-dependent stresses are induced, which can be quantified in-situ during welding and post weld heat treatment. Examples are presented how the conditions to be found during production are simulated in the laboratory. It is shown how welding residual stresses in high-strength steels are affected by the heat control. Elevated working temperatures significantly increase the tensile residual stresses in the heat affected zone (HAZ). The effect of mechanical stresses resulting from welding on stress relief cracking is demonstrated by the example of a creep resistant steel. Reheat cracks were monitored online during post weld heat treatment. T2 - Visual-JW 2019 & WSE 2019 The 5th International Symposium on Visualization in Joining & Welding Science through Advanced Measurements and Simulation & The 8th International Conference of Welding Science and Engineering CY - Osaka, Japan DA - 21.11.2019 KW - Residual stress KW - Restraint KW - Welding KW - Large-scale test KW - Reheat cracking PY - 2019 SP - 83 EP - 84 PB - SEIEI Printing Co., Ltd CY - Osaka, Japan AN - OPUS4-49773 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kannengießer, Thomas A1 - Kromm, Arne A1 - Lausch, Thomas A1 - Schroepfer, Dirk T1 - In-situ Observation of Stress Evolution during High Strength Steel Welding N2 - Residual stresses are crucial when assessing the performance of welded components. The present work deals with the possibilities of transferring the real-life boundary conditions of welding, which influence the residual stress, into the laboratory. The possibilities of a test system with a load capacity of 2 MN specifically developed for online monitoring of stress formation and cracking are shown. Due to the structural design, global process, geometry and material-dependent stresses are induced, which can be quantified in-situ during welding and post weld heat treatment. Examples are presented how the conditions to be found during production are simulated in the laboratory. It is shown how welding residual stresses in high-strength steels are affected by the heat control. Elevated working temperatures significantly increase the tensile residual stresses in the heat affected zone (HAZ). The effect of mechanical stresses resulting from welding on stress relief cracking is demonstrated by the example of a creep resistant steel. Reheat cracks were monitored online during post weld heat treatment. T2 - Visual-JW 2019 & WSE 2019 The 5th International Symposium on Visualization in Joining & Welding Science through Advanced Measurements and Simulation & The 8th International Conference of Welding Science and Engineering CY - Osaka, Japan DA - 21.11.2019 KW - Residual stress KW - Restraint KW - Welding KW - Large-scale test KW - Reheat cracking PY - 2019 AN - OPUS4-49763 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kromm, Arne A1 - Kannengießer, Thomas T1 - Online-Observation of Martensite Formation by combined use of Synchrotron Diffraction and Dilatometry N2 - Welding residual stress engineering by means of an adjusted martensite phase transformation would be highly attractive as detrimental tensile residual stresses may be prevented already during welding without time and cost intensive post processing. The present study shows a synchrotron diffraction analysis of a martensitic steel subjected to thermo-mechanical load cycles. Experiments were conducted regarding the microstructural strain response during the austenite to martensite transformation. The strains are a function of the temperature and the specific loads applied during cooling. The relation between the transformation plasticity of the material, the amount of martensite formed and the arising strains can thus be assessed. The lattice plane specific strains were compared to experimental findings from (macro) dilatation tests. It is shown that the microscopic material behavior differs remarkably from the one observed on the macroscopic scale, what leads to characteristic residual stresses in the material. T2 - Visual-JW 2019 & WSE 2019 The 5th International Symposium on Visualization in Joining & Welding Science through Advanced Measurements and Simulation & The 8th International Conference of Welding Science and Engineering CY - Osaka, Japan DA - 21.11.2019 KW - Martensite KW - Synchrotron KW - Dilatometry KW - Residual stress KW - Phase transformation PY - 2019 AN - OPUS4-49768 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -