TY - JOUR A1 - Ahmadian, A. A1 - Scheiber, D. A1 - Zhou, X. A1 - Gault, B. A1 - Darvishi Kamachali, Reza A1 - Romaner, L. A1 - Ecker, W. A1 - Dehm, G. A1 - Liebscher, C. H. T1 - Interstitial segregation has the potential to mitigate liquid metal embrittlement in iron N2 - The embrittlement of metallic alloys by liquid metals leads to catastrophic material failure and severely impacts their structural integrity. The weakening of grain boundaries by the ingress of liquid metal and preceding segregation in the solid are thought to promote early fracture. However, the potential of balancing between the segregation of cohesion-enhancing interstitial solutes and embrittling elements inducing grain boundary decohesion is not understood. Here, we unveil the mechanisms of how boron segregation mitigates the detrimental effects of the prime embrittler, zinc, in a Σ5 [0 0 1] tilt grain boundary in α −Fe (4 at.% Al). Zinc forms nanoscale segregation patterns inducing structurally and compositionally complex grain boundary states. Ab-initio simulations reveal that boron hinders zinc segregation and compensates for the zinc induced loss in grain boundary cohesion. Our work sheds new light on how interstitial solutes intimately modify grain boundaries, thereby opening pathways to use them as dopants for preventing disastrous material failure. KW - Materials Modelling KW - Liquid Metal Embrittlement KW - Alloy Safety KW - CALPHAD KW - Microstructure Design PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-573576 DO - https://doi.org/10.1002/adma.202211796 SN - 0935-9648 IS - e2211796 PB - Wiley online library AN - OPUS4-57357 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bhadeliya, Ashok A1 - Rehmer, Birgit A1 - Fedelich, Bernard A1 - Jokisch, T. A1 - Skrotzki, Birgit A1 - Olbricht, Jürgen T1 - Fatigue and fracture in dual-material specimens of nickel-based alloys fabricated by hybrid additive manufacturing N2 - The integration of additive manufacturing with traditional processes, termed hybrid additive manufacturing, has expanded its application domain, particularly in the repair of gas turbine blade tips. However, process-related defects in additively manufactured materials, interface formation, and material property mismatches in dual-material structures can significantly impact the fatigue performance of components. This investigation examines the low cycle fatigue and fatigue crack growth behaviors in dual-material specimens of nickel-based alloys, specifically the additively manufactured STAL15 and the cast alloy 247DS, at elevated temperatures. Low cycle fatigue experiments were conducted at temperatures of 950 °C and 1000 °C under a range of strain levels (0.3%–0.8%) and fatigue crack growth tests were conducted at 950 °C with stress ratios of 0.1 and −1. Fractographic and microscopic analyses were performed to comprehend fatigue crack initiation and crack growth mechanisms in the dual-material structure. The results consistently indicated crack initiation and fatigue fracture in the additively manufactured STAL15 material. Notably, fatigue crack growth retardation was observed near the interface when the crack extended from the additively manufactured STAL15 material to the perpendicularly positioned interface. This study highlights the importance of considering yield strength mismatch, as well as the potential effects of residual stresses and grain structure differences, in the interpretation of fatigue crack growth behavior at the interface. KW - Hybrid additive manufacturing KW - Dual-material nickel-based alloys KW - High-temperature fatigue crack growth KW - Low cycle fatigue PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-609340 DO - https://doi.org/10.1016/j.jmrt.2024.08.211 SN - 2238-7854 VL - 32 SP - 3737 EP - 3749 PB - Elsevier B.V. AN - OPUS4-60934 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bhadeliya, Ashok A1 - Rehmer, Birgit A1 - Fedelich, Bernard A1 - Jokisch, T. A1 - Skrotzki, Birgit A1 - Olbricht, Jürgen T1 - Fatigue crack growth behavior of Alloy 247DS brazed joints at high temperatures N2 - Gas turbine components made of nickel-based alloys can be repaired through diffusion brazing. However, process-induced imperfections, defects within the brazing zone, and material property mismatches between the braze alloy and base material may facilitate crack initiation and propagation, ultimately leading to early component failure. To gain insight into the crack growth mechanism and quantitatively characterize fatigue crack growth behavior within brazing zones, fatigue crack growth (FCG) experiments were conducted on brazed joint specimens of nickel-based alloy Alloy 247DS at a temperature of 950 ◦C and a stress ratio R = 0.1. The FCG tests were complemented by fractographic and microstructural analyses, to elucidate the relationship between crack growth mechanisms and the microstructure of the brazed joint. The results demonstrate stable crack propagation within the brazing zone and the nickel-based braze alloy. The latter contains brittle eutectic boride phases and intermetallic phases that reduce the resistance to crack propagation compared to the parent material. This study demonstrates the applicability of standard FCG experimental procedures to fusion zones, thereby enabling a preliminary understanding of crack growth behavior in brazing zones. KW - Diffusion brazing KW - High-temperature fatigue crack growth KW - Nickel-based alloys KW - Alloy 247DS PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-615250 DO - https://doi.org/10.1016/j.msea.2024.147488 SN - 0921-5093 VL - 918 SP - 1 EP - 15 PB - Elsevier B.V. AN - OPUS4-61525 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bhadeliya, Ashok A1 - Rehmer, Birgit A1 - Skrotzki, Birgit A1 - Jokisch, Torsten A1 - Olbricht, Jürgen A1 - Fedelich, Bernard T1 - Fatigue crack growth in nickel-based alloy 247DS with side-brazed pre-sintered preform N2 - Pre-sintered preform (PSP) brazing is employed in the repair of gas turbine components made of nickel-based alloys, including restoring the surface and dimensions of turbine blades and vanes. This study investigates the fatigue crack growth (FCG) behavior of Alloy 247DS specimens with side-brazed PSP material, mimicking a typical sandwich structure formed during such repairs. FCG tests were conducted at an elevated temperature of 950 °C and a stress ratio (R) of 0.1 on specimens with PSP layer thicknesses of 1.5 mm, 2 mm, 3 mm, and 4.5 mm to assess the influence of PSP thickness on fatigue crack growth behavior. Fractographic and metallographic analyses were performed to elucidate the underlying crack growth mechanisms and the microstructural characteristics of both materials. The results revealed that a crack consistently initiated in the PSP material, originating from the starter notch, particularly at the specimen corner during the pre-cracking phase. Additionally, crack propagation in the PSP material consistently advanced ahead of the crack in the Alloy 247DS. This crack growth behavior is attributed to the difference in elastic properties and microstructural differences between the PSP and base material. Metallographic analysis revealed the presence of porosity and brittle precipitates within the PSP material, which led to faster intergranular crack growth. Conversely, Alloy 247DS exhibited transgranular crack growth, contributing to the observed crack propagation behavior. This study demonstrates the applicability of standard FCG testing methods and an approach to characterize the FCG behavior in sandwich specimens, where crack growth occurs simultaneously in both materials, providing a preliminary understanding of crack growth behavior in Alloy 247DS with side-brazed PSP. KW - High-temperature fatigue crack growth (FCG) KW - Nickel-based alloys KW - Alloy 247DS KW - Pre-Sintered Preform (PSP) PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-629783 DO - https://doi.org/10.1016/j.ijfatigue.2025.108961 VL - 197 SP - 1 EP - 13 PB - Elsevier BV AN - OPUS4-62978 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Charmi, Amir A1 - Falkenberg, Rainer A1 - Ávila Calderón, Luis A1 - Mohr, Gunther A1 - Sommer, Konstantin A1 - Ulbricht, Alexander A1 - Sprengel, Maximilian A1 - Saliwan Neumann, Romeo A1 - Evans, Alexander A1 - Skrotzki, Birgit T1 - Mechanical anisotropy of additively manufactured stainless steel 316L: An experimental and numerical study N2 - The underlying cause of mechanical anisotropy in additively manufactured (AM) parts is not yet fully understood and has been attributed to several different factors like microstructural defects, residual stresses, melt pool boundaries, crystallographic and morphological textures. To better understand the main contributing factor to the mechanical anisotropy of AM stainless steel 316L, bulk specimens were fabricated via laser powder bed fusion (LPBF). Tensile specimens were machined from these AM bulk materials for three different inclinations: 0◦, 45◦, and 90◦ relative to the build plate. Dynamic Young’s modulus measurements and tensile tests were used to determine the mechanical anisotropy. Some tensile specimens were also subjected to residual stress measurement via neutron diffraction, porosity determination with X-ray micro-computed tomography (μCT), and texture analysis with electron backscatter diffraction (EBSD). These investigations revealed that the specimens exhibited near full density and the detected defects were spherical. Furthermore, the residual stresses in the loading direction were between −74 ± 24 MPa and 137 ± 20 MPa, and the EBSD measurements showed a preferential ⟨110⟩ orientation parallel to the build direction. A crystal plasticity model was used to analyze the elastic anisotropy and the anisotropic yield behavior of the AM specimens, and it was able to capture and predict the experimental behavior accurately. Overall, it was shown that the mechanical anisotropy of the tested specimens was mainly influenced by the crystallographic texture. KW - Mechanical anisotropy KW - Residual stress KW - Crystal plasticity KW - Selective laser melting (SLM) KW - Laser beam melting (LBM) PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-511719 DO - https://doi.org/10.1016/j.msea.2020.140154 SN - 0921-5093 VL - 799 SP - 140154 PB - Elsevier B.V. AN - OPUS4-51171 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Darvishi Kamachali, Reza T1 - A model for grain boundary thermodynamics N2 - Systematic microstructure design requires reliable thermodynamic descriptions of each and all microstructure elements. While such descriptions are well established for most bulk phases, thermodynamic assessment of microstructure defects is challenging because of their individualistic nature. In this paper, a model is devised for assessing grain boundary thermodynamics based on available bulk thermodynamic data. We propose a continuous relative atomic density field and its spatial gradients to describe the grain boundary region with reference to the homogeneous bulk and derive the grain boundary Gibbs free energy functional. The grain boundary segregation isotherm and phase diagram are computed for a regular binary solid solution, and qualitatively benchmarked for the Pt–Au system. The relationships between the grain boundary's atomic density, excess free volume, and misorientation angle are discussed. Combining the current density-based model with available bulk thermodynamic databases enables constructing databases, phase diagrams, and segregation isotherms for grain boundaries, opening possibilities for studying and designing heterogeneous microstructures. KW - Phase Diagram KW - Thermodynamics KW - Grain boundary PY - 2020 VL - 10 IS - 45 SP - 26728 EP - 26741 AN - OPUS4-51268 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Darvishi Kamachali, Reza T1 - Melting upon Coalescence of Solid Nanoparticles N2 - The large surface-to-volume ratio of nanoparticles is understood to be the source of many interesting phenomena. The melting temperature of nanoparticles is shown to dramatically reduce compared to bulk material. Yet, at temperatures below this reduced melting point, a liquid-like atomic arrangement on the surface of nanoparticles is still anticipated to influence its properties. To understand such surface effects, here, we study the coalescence of Au nanoparticles of various sizes using molecular dynamics simulations. Analysis of the potential energy and Lindemann index distribution across the nanoparticles reveals that high-energy, high-mobility surface atoms can enable the coalescence of nanoparticles at temperatures much lower than their corresponding melting point. The smaller the nanoparticles, the larger the difference between their melting and coalescence temperatures. For small enough particles and/or elevated enough temperatures, we found that the coalescence leads to a melting transition of the two nominally solid nanoparticles, here discussed in relation to the heat released due to the surface reduction upon the coalescence and the size dependence of latent heat. Such discontinuous melting transitions can lead to abrupt changes in the properties of nanoparticles, important for their applications at intermediate temperatures. KW - Nanoparticles KW - Molecular Dynamics KW - Surface-induced Melting PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-552183 DO - https://doi.org/10.3390/solids3020025 VL - 3 IS - 2 SP - 361 EP - 373 PB - MDPI AN - OPUS4-55218 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Darvishi Kamachali, Reza A1 - da Silva, A. A1 - McEniry, E. A1 - Gault, B. A1 - Neugebauer, J. A1 - Raabe, D. T1 - Segregation-assisted spinodal and transient spinodal phase separation at grain boundaries N2 - Segregation to grain boundaries affects their cohesion, corrosion, and embrittlement and plays a critical role in heterogeneous nucleation. In order to quantitatively study segregation and low-dimensional phase separation at grain boundaries, here, we apply a density-based phase-field model. The current model describes the grain-boundary thermodynamic properties based on available bulk thermodynamic data, while the grain-boundary-density profile is obtained using atomistic simulations. To benchmark the performance of the model, Mn grain-boundary segregation in the Fe–Mn system is studied. 3D simulation results are compared against atom probe tomography measurements conducted for three alloy compositions. We show that a continuous increase in the alloy composition results in a discontinuous jump in the segregation isotherm. The jump corresponds to a spinodal Phase separation at grain boundary. For alloy compositions above the jump, we reveal an interfacial transient spinodal phase separation. The transient spinodal phenomenon opens opportunities for knowledge-based microstructure design through the chemical manipulation of grain boundaries. The proposed density-based model provides a powerful tool to study thermodynamics and kinetics of segregation and phase changes at grain boundaries. KW - Grain Boundary Spinodal KW - Densty-based Thermodynamics KW - Microstrucrue Design PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-519497 DO - https://doi.org/10.1038/s41524-020-00456-7 VL - 6 IS - 1 SP - 191 PB - Nature AN - OPUS4-51949 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Darvishi Kamachali, Reza A1 - Wallis, Theophilus A1 - Ikeda, Yuki A1 - Saikia, U. A1 - Ahmadian, A. A1 - Liebscher, C. A1 - Hickel, Tilmann A1 - Maaß, Robert T1 - Giant segregation transition as origin of liquid metal embrittlement in the Fe-Zn system N2 - A giant Zn segregation transition is revealed using CALPHAD-integrated density-based modeling of segregation into Fe grain boundaries (GBs). The results show that above a threshold of only a few atomic percent Zn in the alloy, a substantial amount of up to 60 at.% Zn can segregate to the GB. We found that the amount of segregation abruptly increases with decreasing temperature, while the Zn content in the alloy required for triggering the segregation transition decreases. Direct evidence of the Zn segregation transition is obtained using high-resolution scanning transmission electron microscopy. Base on the model, we trace the origin of the segregation transition back to the low cohesive energy of Zn and a miscibility gap in Fe-Zn GB, arising from the magnetic ordering effect, which is confirmed by ab-initio calculations. We also show that the massive Zn segregation resulting from the segregation transition greatly assists with liquid wetting and reduces the work of separation along the GB. The current predictions suggest that control over Zn segregation, by both alloy design and optimizing the galvanization and welding processes, may offer preventive strategies against liquid metal embrittlement. KW - CALPHAD KW - Microstructure Design KW - Grain boundary engineering KW - Steels KW - Density-based Model KW - Segregation Engineering PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-584292 DO - https://doi.org/10.1016/j.scriptamat.2023.115758 SN - 1359-6462 SN - 1872-8456 VL - 238 SP - 1 EP - 5 PB - Elsevier CY - Amsterdam AN - OPUS4-58429 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Darvishi Kamachali, Reza A1 - Wang, L. T1 - Elastic energy of multi-component solid solutions and strain origins of phase stability in high-entropy alloys N2 - The elastic energy of mixing for multi-component solid solutions is derived by generalizing Eshelby's sphere-in-hole model. By surveying the dependence of the elastic energy on the chemical composition and lattice misfit, we derive a lattice strain coefficient λ*. Studying several high-entropy alloys and superalloys, we propose that most solid solution multi-component alloys are stable when λ*<0.16, generalizing the Hume-Rothery atomic-size rule for binary alloys. We also reveal that the polydispersity index δ, frequently used for describing strain in multi-component alloys, directly represents the elastic energy e with e=qδ², q being an elastic constant. Furthermore, the effects of (i) the number and (ii) the atomic-size distribution of constituting elements on the phase stability of high-entropy alloys were quantified. The present derivations and discussions open for richer considerations of elastic effects in high-entropy alloys, offering immediate support for quantitative assessments of their thermodynamic properties and studying related strengthening mechanisms. KW - Ordering KW - High-entropy alloys KW - Alloy design KW - Strain energy KW - Phase stability PY - 2022 DO - https://doi.org/10.1016/j.scriptamat.2021.114226 SN - 1359-6462 VL - 206 SP - 1 EP - 6 PB - Elsevier CY - Amsterdam AN - OPUS4-53427 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Dub, S. A1 - Haftaoglu, Cetin A1 - Kindrachuk, Vitaliy T1 - Estimate of theoretical shear strength of C60 single crystal by nanoindentation N2 - The onset of plasticity in a single crystal C60 fullerite was investigated by nanoindentation on the (111) crystallographic plane. The transition from elastic to plastic deformation in a contact was observed as pop-in events on loading curves. The respective resolved shear stresses were computed for the octahedral slip systems ⟨011¯¯¯⟩{111}, supposing that their activation resulted in the onset of plasticity. A finite element analysis was applied, which reproduced the elastic loading until the first pop-in, using a realistic geometry of the Berkovich indenter blunt tip. The obtained estimate of the C60 theoretical shear strength was about 1/11 of the shear modulus on {111} planes. KW - Finite element analysis KW - Fullerite KW - Nanoindentation PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-523208 DO - https://doi.org/10.1007/s10853-021-05991-2 VL - 56 IS - 18 SP - 10905 EP - 10914 PB - Springer Nature AN - OPUS4-52320 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Elfetni, Seif A1 - Darvishi Kamachali, Reza T1 - PINNs-MPF: A Physics-Informed Neural Network framework for Multi-Phase-Field simulation of interface dynamics N2 - We present PINNs-MPF framework, an application of Physics-Informed Neural Networks (PINNs) to handle Multi-Phase-Field (MPF) simulations of microstructure evolution. A combination of optimization techniques within PINNs and in direct relation to MPF method are extended and adapted. The numerical resolution is realized through a multi-variable time-series problem by using fully discrete resolution. Within each interval, space, time, and phases/grains are treated separately, constituting discrete subdomains. PINNs-MPF is equipped with an extended multi-networking (parallelization) concept to subdivide the simulation domain into multiple batches, with each batch associated with an independent NN trained to predict the solution. To ensure continuity across the spatio-temporal-phasic subdomains, a Master NN efficiently is to handle interactions among the multiple networks and facilitates the transfer of learning. A pyramidal training approach is proposed to the PINN community as a dual-impact method: to facilitate the initialization of training when dealing with multiple networks, and to unify the solution through an extended transfer of learning. Furthermore, a comprehensive approach is adopted to specifically focus the attention on the interfacial regions through a dynamic meshing process, significantly simplifying the tuning of hyper-parameters, serving as a key concept for addressing MPF problems using machine learning. We perform a set of systematic simulations that benchmark foundational aspects of MPF simulations, i.e., the curvature-driven dynamics of a diffuse interface, in the presence and absence of an external driving force, and the evolution and equilibrium of a triple junction. The proposed PINNs-MPF framework successfully reproduces benchmark tests with high fidelity and Mean Squared Error (MSE) loss values ranging from 10^−6 to 10^−4 compared to ground truth solutions. KW - Machine learning KW - PINNs KW - Phase-field method KW - Microstructure evolution KW - Parallel training KW - Neural networks PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-629740 DO - https://doi.org/10.1016/j.enganabound.2025.106200 SN - 0955-7997 VL - 176 SP - 1 EP - 22 PB - Elsevier CY - Amsterdam AN - OPUS4-62974 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Elfetni, Seifallah A1 - Darvishi Kamachali, Reza T1 - PINNs-MPF: An Efficient Physics-Informed Machine Learning-based Solver for Multi-Phase-Field Simulations using Tensorflow N2 - This paper introduces PINNs-MPF, a novel Machine Learning-based solver designed for Multi-Phase-Field (MPF) and diffuse interface simulations, offering innovative approaches to address complex challenges in addressing microstructure evolution in polycrystalline materials using Machine Learning. The framework not only surpasses current limitations in handling multi-phase problems but also allows for potential upscaling to tackle more intricate scenarios. Developed in Python, the related code leverages optimized libraries like TensorFlow, showcasing efficiency and potential scalability in materials science and engineering simulations. This framework, integrating advanced techniques such as multi-networking and training optimization, setting a new standard in predictive capabilities and understanding complex physical phenomena. KW - Machine Learning KW - Microstructure Simulation KW - Phase Field PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-631917 DO - https://doi.org/10.1016/j.simpa.2025.100753 SN - 2665-9638 VL - 24 SP - 1 EP - 4 PB - Elsevier B.V. AN - OPUS4-63191 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Epishin, A. A1 - Camin, B. A1 - Hansen, L. A1 - Heuser, M. A1 - Lopez-Galilea, I. A1 - Ruttert, B. A1 - Theisen, W. A1 - Fedelich, Bernard T1 - Refinement and Experimental Validation of a Vacancy Model of Pore Annihilation in Single-Crystal Nickel-Base Superalloys during Hot Isostatic Pressing N2 - Initially, as-cast and homogenized single crystals of nickel-base superalloy CMSX-4 are subjected to hot isostatic pressing at 1288 °C. Two series of experiments are conducted: under the same pressure of 103 MPa but with different durations, between 0.5 and 6 h, and under different pressures, between 15 and 150 MPa, but for the same time of 0.5 h. The porosity annihilation is investigated metallographically and by high-resolution synchrotron X-ray tomography. The obtained experimental results are compared with the predictions of the vacancy model proposed recently in the group. Herein, the model is further refined by coupling with X-ray tomography. The model describes the evolution of the pore arrays enclosed in the 3D synchrotron tomograms during hot isostatic pressing and properly predicts the time and stress dependences of the pore annihilation kinetics. The validated model and the obtained experimental results are used for selecting the optimal technological parameters such as applied pressure and processing time KW - Superalloys KW - HIP KW - Single-Crystal KW - Diffusion PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-526859 DO - https://doi.org/10.1002/adem.202100211 VL - 23 IS - 7 SP - 211 AN - OPUS4-52685 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Epishin, A. A1 - Fedelich, Bernard A1 - Finn, Monika A1 - Künecke, Georgia A1 - Rehmer, Birgit A1 - Nolze, Gert A1 - Leistner, C. A1 - Petrushin, N. A1 - Svetlov, I. T1 - Investigation of Elastic Properties of the Single-Crystal Nickel-Base Superalloy CMSX-4 in the Temperature Interval between Room Temperature and 1300 °C N2 - The elastic properties of the single-crystal nickel-base superalloy CMSX-4 used as a blade material in gas turbines were investigated by the sonic resonance method in the temperature interval between room temperature and 1300 °C. Elastic constants at such high temperatures are needed to model the mechanical behavior of blade material during manufacturing (hot isostatic pressing) as well as during technical accidents which may happen in service (overheating). High reliability of the results was achieved using specimens of different crystallographic orientations, exciting various vibration modes as well as precise measurement of the material density and thermal Expansion required for modeling the resonance frequencies by finite element method. Combining the results measured in this work and literature data the elastic constants of the gamma and gamma' phases were predicted. This prediction was supported by measurement of the temperature dependence of the gamma'fraction. All data obtained in this work are given in numerical or analytical forms and can be easily used for different scientific and engineering calculations. KW - Nickel-base superalloys KW - Single-crystals KW - Characterization KW - Elastic constants PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-520972 DO - https://doi.org/10.3390/cryst11020152 VL - 11 IS - 2 SP - 152 PB - MDPI AN - OPUS4-52097 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Epishin, A. I. A1 - Fedelich, Bernard A1 - Viguier, B. A1 - Schriever, Sina A1 - Svetlov, I. L. A1 - Petrushin, N. V. A1 - Saillard, R. A1 - Proietti, A. A1 - Poquillon, D. A1 - Chyrkin, A. T1 - Creep of single-crystals of nickel-base γ-alloy at temperatures between 1150 °C and 1288 °C N2 - A γ-analogue of the superalloy CMSX-4 that does not contain the strengthening γ′ -phase and only consists of the γ-solid solution of nickel has been designed, solidified as single-crystals of different orientations, and tested under creep conditions in the temperature range between 1150 and 1288 °C. The tests have revealed a very high creep anisotropy of this alloy, as was previously found for CMSX-4 at supersolvus temperature of 1288 °C. This creep anisotropy could be explained by the dominance of 〈011〉{111} octahedral slip. Furthermore, the analysis of the creep data has yielded a high value of the creep activation energy, Qc≈442 kJ/mol, which correlates with the high activation energy of Re diffusion in Ni. This supports the hypothesis that dislocation motion in the γ-matrix of Re-containing superalloys is controlled by the diffusion of the Re atoms segregating at the dislocation core. The Norton stress exponent n is close to 5, which is a typical value for pure metals and their alloys. The absence of γ′ -reprecipitation after high-temperature creep tests facilitates microstructural investigations. It has been shown by EBSD that creep deformation results in an increasing misorientation of the existing low angle boundaries. In addition, according to TEM, new low angle boundaries appear due to reactions of the a/2 〈011〉 mobile dislocations and knitting of new networks. KW - Nickel alloys KW - Single-crystals KW - Creep KW - Electron microscopy KW - Deformation mechanisms PY - 2021 DO - https://doi.org/10.1016/j.msea.2021.141880 SN - 0921-5093 VL - 825 SP - 1 EP - 13 PB - Elsevier CY - Amsterdam AN - OPUS4-53132 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Falkenberg, Rainer A1 - Kamachali, Reza Darvishi T1 - Segregation-induced hydrogen embrittlement in titanium N2 - Although titanium offers an optimal combination of strength, low weight, and toughness for various applications, it suffers from a drawback: loss of ductility upon exposure to hydrogen. In this work, we couple CALPHAD-integrated density-based thermodynamic modelling of hydrogen segregation with an experimentally calibrated fracture model to investigate its on crack propagation in titanium. Here we propose to model the crack propagation path as a quasi-interface with slightly opened structure and reduced atomic density, enabling interstitial hydrogen segregation. The atomic density is then directly linked with the damage parameter. We found that hydrogen segregation in titanium undergoes a significant transition such that above a threshold of only few atomic percent hydrogen in the solid solution, the interfacial hydrogen concentration exceeds 20 at.%. Integrating this information into our fracture model, the material damage evolution could be explained by a segregation-affected Griffith crack energy, resulting in material decohesion. We found that the segregation transition and subsequent embrittlement effects are critically sensitive to the temperature in the system. The present results suggest a mechanism underlying the sudden loss of fracture toughness during crack propagation, in relation to the ductile-to-brittle transition observed in titanium alloys exposed to hydrogen. The proposed CALPHAD-integrated chemo-mechanical framework can be further generalised for studying more complex failure mechanisms in various materials. KW - Segregation transition KW - Hydrogen embrittlement KW - Titanium alloys KW - Crack propagation KW - Ductile-to-brittle transition PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-655451 DO - https://doi.org/10.1016/j.mtla.2025.102411 SN - 2589-1529 VL - 41 SP - 1 EP - 12 PB - Elsevier Inc. AN - OPUS4-65545 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Fantin, Andrea A1 - Manzoni, Anna Maria A1 - Springer, H. A1 - Darvishi Kamachali, Reza A1 - Maaß, Robert T1 - Local lattice distortions and chemical short-range order in MoNbTaW N2 - Extended X-ray absorption fine structure (EXAFS) conducted on an equiatomic MoNbTaW bcc medium-entropy alloy that was annealed at 2273 K reveals unexpectedly small 1st and 2nd shell element-specific lattice distortions. An experimental size-mismatch parameter, δexp, is determined to be ca. 50% lower than the corresponding calculated value. Around W, short-range order (SRO) preferring 4d elements in the 1st and 2nd shells persists. A Nb-W ordering is found, which is reminiscent of ordering emerging at lower temperatures in the B2(Mo,W;Ta,Nb)- and B32(Nb,W)-phases. With high-temperature ordering preferences in fcc also foreshadowing low-temperature phase, these findings suggest a general feature of high-temperature SRO. KW - High Entropy Alloys KW - Short-range order KW - Lattice distortions KW - EXAFS PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-598164 DO - https://doi.org/10.1080/21663831.2024.2326014 SN - 2166-3831 VL - 12 IS - 5 SP - 346 EP - 354 PB - Taylor & Francis AN - OPUS4-59816 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Feldmann, Titus A1 - Fedelich, Bernard A1 - Epishin, A. T1 - Simulation of Hot Isostatic Pressing in a Single-Crystal Ni Base Superalloy with the Theory of Continuously Distributed Dislocations Combined with Vacancy Diffusion N2 - Single-crystal components made of nickel base superalloys contain pores after casting and homogenization heat treatment. Hot isostatic pressing (HIP), which is carried above the γ' -solvus temperature of the alloy, is industrially applied to reduce porosity. A modeling of HIP based on continuously distributed dislocations is developed in a 2D setting. Glide and climb of straight-edge dislocations, as well as vacancy diffusion, are the deformation mechanisms taken into account. Thereby, dislocation glide is controlled by dragging a cloud of large atoms, and climb is controlled by vacancy diffusion. Relying on previous investigations of the creep behavior at HIP temperatures, it is assumed that new dislocations are nucleated at low-angle boundaries (LAB) and move through subgrains until they either reach the opposite LABs or react with other dislocations and annihilate. Vacancies are created at the pore surface and diffuse through the alloy until they are either consumed by climbing dislocations or disappear at the LABs. The field equations are solved by finite elements. It is shown that pore shrinking is mostly controlled by vacancy diffusion as the shear stresses at the LABs are too low to nucleate a sufficient amount of dislocations. KW - Nickel-base superalloys KW - HIP KW - Dislocation KW - Creep KW - Model PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-542309 DO - https://doi.org/10.1002/adem.202101341 VL - 2022 PB - Wiley AN - OPUS4-54230 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ferrari, Bruno A1 - Fantin, Andrea A1 - Said, D. A1 - Fitch, A. N. A1 - Suárez Ocano, Patricia A1 - Mishurova, Tatiana A1 - Roveda, Ilaria A1 - Kromm, Arne A1 - Darvishi Kamachali, Reza A1 - Bruno, Giovanni A1 - Evans, Alexander A1 - Requena, G. A1 - Agudo Jácome, Leonardo A1 - Serrano Munoz, Itziar T1 - The impact of scanning strategy on cell structures in PBF-LB/M/IN718: an in situ synchrotron x-ray diffraction study N2 - In additive manufacturing, any change of the process parameters, such as scanning strategy, directly affects the cooling rates, heat accumulation, and overall thermal history of the build. Consequently, parts built with different process parameters tend to have different levels of crystallographic texture, residual stress, and dislocation density. These features can influence the properties of the material and their development during post-processing operations. In this study, IN718 prisms were built by laser powder bed fusion (PBF-LB/M) using two different scanning strategies (continuous 67° rotations around the build direction, ROT, and alternating 0°/67° scans, ALT) to provide two different as-built conditions. In situ time-resolved synchrotron diffraction was performed during a solution heat treatment at 1027 °C for 1 h. Ex situ scanning electron microscopy was used to support and complement the in situ observations. An approach to quantify the effect of elemental microsegregation at the cell walls is developed based on the deconvolution of asymmetric γ-nickel matrix peaks. Following this approach, the scanning strategies are shown to affect the as-built fraction of cell walls in the material, resulting in a difference of approximately 5 %, in weight fraction, between ROT and ALT (19 % vs. 24 %, respectively). This microsegregation was observed to be rapidly homogenized during the heating ramp, and no significant changes to the peak shape in the γ peaks occurred during the isothermal part of the heat treatment, regardless of the scanning strategy. KW - Additive manufacturing KW - Inconel 718 KW - Synchrotron x-ray diffraction KW - Heat treatment KW - Laser powder bed fusion KW - Cellular microstructure PY - 2026 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-650958 DO - https://doi.org/10.1016/j.jmrt.2025.11.214 SN - 2238-7854 VL - 41 SP - 593 EP - 608 PB - Elsevier B.V. AN - OPUS4-65095 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gesell, Stephan A1 - Ganesh, R. A1 - Fedelich, Bernard A1 - Kuna, M. A1 - Kiefer, B. T1 - Numerical calculation of 𝛥CTOD to simulate fatigue crack growth under large scale viscoplastic deformations N2 - Crack propagation under low cycle fatigue and thermomechanical fatigue is characterized by high plastic and creep strains that extend over large regions around the crack, so that concepts of linear-elastic fracture mechanics cannot be applied. In these cases, the cyclic crack tip opening displacement 𝛥CTOD is a promising loading parameter to quantify crack growth. In this work, suitable definitions and Finite Element techniques are investigated and compared for an accurate calculation of 𝛥CTOD under cyclic mechanical and/or thermal loading. A viscoplastic temperature dependent material model of Chaboche-type is used along with large strain settings, specified for the austenitic cast iron Ni-resist. Extensive two-dimensional analyses of Single Edge Notch Tension specimens revealed that collapsed special crack tip elements are superior compared with commonly used regular quadrilateral 8-node elements. At the same level of accuracy of 𝛥CTOD, they require an about ten times coarser mesh and show less sensitivity w.r.t. element size for both stationary and propagating cracks. In order to simulate fatigue crack growth, an efficient, fully automated FE-technique is developed for an incremental crack propagation by successive remeshing, whereby the deformations and internal state variables are mapped from the old mesh onto the new one. Recommendations are made regarding important numerical control parameters like optimal size of crack tip elements, length of crack growth increment in relation to plastic zone size and 𝛥CTOD value. KW - Crack tip opening displacement KW - Finite element analysis KW - Crack growth KW - Low cycle fatigue PY - 2023 DO - https://doi.org/10.1016/j.engfracmech.2023.109064 VL - 281 IS - 109064 SP - 1 EP - 23 PB - Elsevier Ltd. AN - OPUS4-56857 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Haapalehto, Matias A1 - Pinomaa, Tatu A1 - Wang, Lei A1 - Laukkanen, Anssi T1 - An atomistic simulation study of rapid solidification kinetics and crystal defects in dilute Al–Cu alloys N2 - Rapid solidification kinetics of dilute Al–Cu alloys is simulated using a quantum mechanics based bondorder potential (BOP), in free solidification conditions, to determine kinetic and thermodynamic properties of solidification, as well as point defects and chemical ordering of the solidified structures. We measure the anisotropic kinetic coefficient, anisotropic solid–liquid interface energy, as well as solute trapping kinetics in terms of partition coefficient versus velocity and solute drag coefficient. Furthermore, solid–liquid interface free energy and its anisotropy are measured in equilibrium simulations, showing reasonably good agreement with previous studies. We also verified the self-consistency of the MD simulations, by comparing the interfacial temperature vs. velocity to that predicted by the continuous growth model. These solid–liquid interface properties are important for quantitative parametrization of larger scale solidification modeling techniques such as phase field models. We also investigated the point defect content, local chemical ordering, and local crystalline structures in the rapidly solidified samples. We found clustering of solute with vacancies, whereas copper atoms repelled each other in these dilute alloy simulations. In addition to vacancies, a large number of interstitials were found. In solidification velocities approaching the complete solute trapping regime, we found that the vacancies and interstitials formed in conjunction, i.e. as Frenkel pairs. Finally, in addition to FCC, we detected BCC and HCP phases, where the latter two were accompanied by an increase in local copper content. Understanding the formation of point defects and their relationship to chemical ordering is an important step towards controlling the formation of pre-precipitates and precipitates, which are an important strengthening mechanism for aluminum–copper alloys. KW - Rapid solidification KW - Aluminum–copper KW - MD PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-628722 DO - https://doi.org/10.1016/j.commatsci.2022.111356 SN - 0927-0256 VL - 209 SP - 1 EP - 13 PB - Elsevier CY - Amsterdam AN - OPUS4-62872 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hickel, Tilmann A1 - Waske, Anja A1 - Tehranchi, Ali A1 - Bhattacharya, Biswajit A1 - Stawski, Tomasz M. A1 - Fellinger, Tim-Patrick A1 - Mehmood, Asad A1 - Witt, Julia A1 - Ozcan, Ozlem A1 - Guilherme Buzanich, Ana A1 - Kumar, Sourabh A1 - Mishra, Rajesh Kumar A1 - Holzer, Marco A1 - Stucchi de Camargo, Andrea Simone A1 - Agudo Jácome, Leonardo A1 - Manzoni, Anna A1 - Fantin, Andrea A1 - John, Elisabeth A1 - Hodoroaba, Vasile-Dan A1 - Bührig, Sophia A1 - Murugan, Jegatheesan A1 - Marschall, Niklas A1 - George, Janine A1 - Darvishi Kamachali, Reza A1 - Maaß, Robert A1 - Emmerling, Franziska T1 - Chemically complex materials enable sustainable high-performance materials N2 - Chemically complex materials (CCMats) 􀀀 including high-entropy alloys, oxides, and related multi-principal element systems 􀀀 offer a paradigm shift in materials design by leveraging chemical diversity to simultaneously optimize functional, structural, and sustainability criteria. The vastness of the compositional and structural space in CCMats propels the field into an expanding exploratory state. To reconcile functional and structural performance across this immense parameter space remains an open challenge. This Perspective evaluates the opportunities and challenges associated with harnessing chemical complexity across a broad spectrum of applications, such as hydrogen storage, ionic conductors, catalysis, magnetics, dielectrics, semiconductors, optical materials, and multifunctional structural systems. It is delineated how three central design strategies: targeted substitution (SUB), defect engineering (DEF), and diversity management (DIV) enable the reconciliation of high functional performance with long-term structural stability and environmental responsibility. Advances in computational thermodynamics, microstructure simulations, machine learning, and multimodal characterization are accelerating the exploration and optimization of CCMats, while robust data infrastructures and automated synthesis workflows are emerging as essential tools for navigating their complex compositional space. By fostering cross-disciplinary knowledge transfer and embracing data-driven design, CCMats are poised to deliver next-generation materials solutions that address urgent technological, energy, and environmental demands. KW - Chemically complex materials KW - Structural stability KW - Functional performance KW - Design strategies KW - Sustainability PY - 2026 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-655598 UR - https://www.sciencedirect.com/science/article/pii/S1359028626000033?via%3Dihub DO - https://doi.org/10.1016/j.cossms.2026.101256 SN - 1359-0286 VL - 42 SP - 1 EP - 26 PB - Elsevier Ltd. CY - Amsterdam AN - OPUS4-65559 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ikeda, Yuki A1 - Han, Seungchang A1 - Wallis, Theophilus A1 - Darvishi Kamachali, Reza A1 - Maaß, Robert T1 - On the preference of liquid-metal embrittlement along high-angle grain-boundaries in galvanized steels N2 - Focusing on the early stages of liquid-metal embrittlement (LME) of Zinc (Zn) coated advanced high-strength steels, we show that the Zn infiltration path prior to grain-boundary decohesion and therefore cracking distinctly follows high-angle grain boundaries (HAGBs). This selective transport prior to LME-induced microcracking rationalizes the experimentally observed post-mortem cracking along martensitic HAGBs. We discuss the selective Zn transport and GB-weakening in terms of an misorientation-angle dependent atomic density and diffusivity, and its effect on GB-segregation. KW - Liquid-metal embrittlement KW - Advanced high-strength steels KW - Grain boundaries PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-631103 DO - https://doi.org/10.1016/j.scriptamat.2025.116723 SN - 1359-6462 VL - 265 SP - 1 EP - 5 PB - Elsevier Inc. AN - OPUS4-63110 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ikeda, Yuki A1 - Ni, H.C. A1 - Chakraborty, A. A1 - Ghassemi-Armaki, H. A1 - Zuo, J.M. A1 - Darvishi Kamachali, Reza A1 - Maaß, Robert T1 - Segregation-induced grain-boundary precipitation during early stages of liquid-metal embrittlement of an advanced high-strength steel N2 - Liquid-metal embrittlement (LME) of galvanized (Zn-coated) advanced high-strength steels is a long-known problem in materials science. Here we reveal the initial microstructural processes underneath the Zn-coating that lead to LME-microcrack initiation in the steel substrate. We track the microstructural evolution during the first tens of milliseconds and find pronounced signatures of Fe-Zn intermetallic precipitation in both ferrite grain boundaries and at internal ferrite-oxide phase boundaries. In concert with novel CALPHAD-integrated density-based thermodynamic modelling, we demonstrate that Zn-rich intermetallic phase-nucleation can occur at markedly low processing temperatures due to a segregation transition. We show that a small Znenrichment caused by Zn bulk-diffusion during the initial temperature rise in a joining process is sufficient to induce the segregation transition and subsequent nucleation of Fe-Zn intermetallic grain-boundary phases, which the experiments link to crack initiation sites. These findings direct focus onto LME-controlling microstructural and thermodynamic phenomena at temperatures below the ductility trough and the austenite formation temperature. KW - Resistance spot welding KW - Liquid-metal embrittlement KW - Steels KW - Grain boundaries PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-581067 DO - https://doi.org/10.1016/j.actamat.2023.119243 VL - 259 SP - 1 EP - 12 PB - Elsevier Ltd AN - OPUS4-58106 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ikeda, Yuki A1 - Wallis, Theophilus A1 - Maaß, Robert A1 - Darvishi Kamachali, Reza T1 - Thermodynamics of grain boundary segregation transition and their relevance for liquid metal embrittlement in Fe-Zn system N2 - Grain boundaries (GBs) are common sites of failure in polycrystalline materials. Recently, a massive Zn segregation transition at Fe GBs was discovered and shown to act as a potent precursor of liquid metal embrittlement (LME) in the Fe-Zn system (Kamachali et al., Scripta Materialia 238 (2024) 115758). In this study, we elaborate on how temperature, GB type and the chemo-structurally coupled phase decomposition at the GB impact this segregation transition. CALPHAD and atomistic simulation data were utilized as inputs to conduct quantitative density-based thermodynamic modeling and phase-field simulations across various GBs, alloy compositions, and temperatures. We reveal that once the segregation transition becomes possible, the GB structural variation stabilizes spinodally formed Zn-rich phases within the GB region, with a higher tendency in disordered GBs. GB phase diagrams were constructed to identify and analyze the range of critical temperatures and alloy compositions associated with the segregation transition. The phase diagrams reveal that the miscibility gap for more disordered GB expands and, although the segregation transition is inevitable and occurs for all GBs, the barrier to triggering it is lower for more disordered GBs. Based on our thermodynamic analyses, potential processing modifications and GB engineering strategies for mitigating segregation-induced LME are thoroughly discussed. KW - Thermodynamics KW - Phase-Field Modelling KW - Steels PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-634145 DO - https://doi.org/10.1016/j.actamat.2025.121134 SN - 1359-6454 VL - 296 SP - 1 EP - 11 PB - Elsevier BV AN - OPUS4-63414 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Jacobson, D. A1 - Darvishi Kamachali, Reza A1 - Thompson, G. B. T1 - Extending Density Phase-Field Simulations to Dynamic Regimes N2 - Density-based phase-field (DPF) methods have emerged as a technique for simulating grain boundary thermodynamics and kinetics. Compared to the classical phase-field, DPF gives a more physical description of the grain boundary structure and chemistry, bridging CALPHAD databases and atomistic simulations, with broad applications to grain boundary and segregation engineering. Notwithstanding their notable progress, further advancements are still warranted in DPF methods. Chief among these are the requirements to resolve its performance constraints associated with solving fourth-order partial differential equations (PDEs) and to enable the DPF methods for simulating moving grain boundaries. Presented in this work is a means by which the aforementioned problems are addressed by expressing the density field of a DPF simulation in terms of a traditional order parameter field. A generic DPF free energy functional is derived and used to carry out a series of equilibrium and dynamic simulations of grain boundaries in order to generate trends such as grain boundary width vs. gradient energy coefficient, grain boundary velocity vs. applied driving force, and spherical grain radius vs. time. These trends are compared with analytical solutions and the behavior of physical grain boundaries in order to ascertain the validity of the coupled DPF model. All tested quantities were found to agree with established theories of grain boundary behavior. In addition, the resulting simulations allow for DPF simulations to be carried out by existing phase-field solvers. KW - CALPHAD KW - Phase-field modelling KW - Phase-Field Simulations PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-581365 DO - https://doi.org/10.3390/met13081497 VL - 13 SP - 1 EP - 16 AN - OPUS4-58136 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Jacobson, David A1 - Darvishi Kamachali, Reza A1 - Thompson, Gregory T1 - Coupling density phase field models with atomistic potentials N2 - A density-based phase field model is developed where the free energy functional is explicitly linked with molecular dynamics and is referred to as the Molecular Phase Field Method (MoPF). MoPF simulations involve expressing interatomic potentials in terms of density to form a density based free energy functional. Inputs to this functional are taken from atomistics such that the phase field density profile matches the corresponding density profile from atomistic simulations. We analyze our results by comparing the MoPF calculated excess interfacial energies with excess interfacial energies calculated using molecular dynamics associated with several nickel grain boundaries. Additionally, a comparison is made between our results and the interfacial energies of a \Sigma7 boundary across a variety of FCC systems simulated using density functional theory. The MoPF method is able to successfully predict grain boundary free energy trends between grain boundary and material types offering an atomistically informed mesoscale formulation for studying grain boundary physics. KW - Density-based Phase-Field Modelling KW - Atomistic Simulation KW - Grain Boundary PY - 2024 DO - https://doi.org/10.1016/j.commatsci.2023.112763 VL - 233 SP - 1 EP - 6 PB - Elsevier AN - OPUS4-59360 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Jentzsch, Stefan A1 - Stock, Daniel A1 - Häcker, Ralf A1 - Skrotzki, Birgit A1 - Darvishi Kamachali, Reza A1 - Klingbeil, Dietmar A1 - Kindrachuk, Vitaliy T1 - Shear Band Formation with Split Hopkinson Bar Experiments N2 - The essence of dynamic failure is closely linked to dramatic shear deformations which often lead to the formation of adiabatic shear bands (ASB). Under high loading velocities and the subsequent rapid temperature increase, the localization of shear strain is crucial in view of safety issues of systems in mechanical and aircraft engineering, especially with respect to fast rotating components and diverse crash scenarios. In this research, we perform high speed impact tests at the split Hopkinson pressure bar (SHPB) setup and use particular hat-shaped specimen geometries that resemble the stresses and failure conditions at the component level. In the first step, we specify a notched specimen geometry using finite element (FE) simulations to ensure pure shear. Further, quasi-static compressive tests and a series of impact tests at high strain rates of 10^3-10^4 s^-1 are conducted on specimens manufactured from a fine-grain structural steel with the properties of S355. Optical microscopy and electron backscatter diffraction (EBSD) of the sheared zones unveil significant localization to maximal shear strains of about 0.9 accompanied by grain refinement by factors 5 to 14. The displacements across the surface of the specimens are captured with subset-based local digital image correlation (DIC) during the impact time, and serve as an objective to validate a viscoplastic constitutive relationship. More precisely, the deformation distribution is accurately reproduced by the widely recognized Johnson-Cook (JC) model, which features an enhanced description of damage evolution. Thus, combining experimental and characterization techniques, continuum mechanics and reasonable optimization strategies for the identification of model parameters provides an efficient approach for comprehensive insights into the strain localization behaviour and its impact on the mechanical performance of S355 under extreme strain rates and deformations. KW - Adiabatic shear bands KW - Finite element analysis KW - Viscoplastic material modelling KW - Split Hopkinson pressure bar KW - Hat-shaped specimen KW - Johnson–Cook parameter identification PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-613339 DO - https://doi.org/10.1016/j.ijmecsci.2024.109749 VL - 284 SP - 1 EP - 14 PB - Elsevier BV AN - OPUS4-61333 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Jürgens, Maria A1 - Sonntag, Nadja A1 - Olbricht, Jürgen A1 - Fedelich, Bernard A1 - Skrotzki, Birgit T1 - The effect of dwell times on the thermomechanical fatigue life performance of grade P92 steel at intermediate and low strain amplitudes N2 - Results of an extended TMF test program on grade P92 steel in the temperature range of 620 °C - 300 °C, comprising in-phase (IP) and out-of-phase (OP) tests, partly performed with symmetric dwells at Tmax/Tmin, are presented. In contrast to previous studies, the low-strain regime is also illuminated, which approaches flexible operation in a power plant with start/stop cycles. At all strain amplitudes, the material performance is characterized by continuous cyclic softening, which is retarded in tests at lower strains but reaches similar magnitudes in the course of testing. In the investigated temperature range, the phase angle does not affect fatigue life in continuous experiments, whereas the IP condition is more detrimental in tests with dwells. Fractographic analyses indicate creep-dominated and fatigue-dominated damage for IP and OP, respectively. Analyses of the (micro)hardness distribution in the tested specimens suggest an enhanced microstructural softening in tests with dwell times for the low- but not for the high-strain regime. To rationalize the obtained fatigue data, the fracture-mechanics-based D_TMF concept, which was developed for TMF life assessment of ductile alloys, was applied. It is found that the D_TMF parameter correlates well with the measured fatigue lives, suggesting that subcritical growth of cracks (with sizes from a few microns to a few millimeters) governs failure in the investigated range of strain amplitudes. KW - 9-12%Cr steel KW - Thermomechanical fatigue KW - Symmetric dwell periods KW - Low strain KW - Parametric modeling PY - 2021 DO - https://doi.org/10.1016/j.msea.2020.140593 VL - 805 SP - 140593 PB - Elsevier B.V. AN - OPUS4-52374 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kianinejad, Kaveh A1 - Czediwoda, Fabian A1 - Glatzel, U. A1 - Völkl, R. A1 - Stöhr, B. A1 - Ávila Calderón, Luis A1 - Schriever, Sina A1 - Saliwan Neumann, Romeo A1 - Fedelich, Bernard A1 - Darvishi Kamachali, Reza T1 - Microstructure-based modelling of the anisotropic creep behaviour in additively manufactured INCONEL 718 N2 - The existing gap in the adequate prediction of the microstructure-property relationships remains a significant barrier to the safe application of the additively manufactured materials. This challenge is fundamentally tied to the intricate microstructural defects that emerge during the processing. Systematic microstructure-based modelling can offer solutions to address this bottleneck. In this work, we utilize a crystal plasticity model, developed for gamma''-strengthened Ni-base alloys and calibrated with single crystal tensile and creep tests of Inconel 718. By systematically refining the representative volume element complexity---from equiaxed to elongated grain morphologies, and from unimodal to bimodal orientation and grain size distributions---we demonstrate how each layer of structural realism contributes to the model’s predictive capacity. Creep tests of laser-based powder bed fusion (PBF-LB/M) manufactured samples in three orientations (with the tensile axis parallel, perpendicular, and 45° tilted relative to the building direction) were performed at 650° C, accompanied by electron backscatter secondary diffraction measurements. The results of our simulations reveal that the bimodal grain morphology and crystallographical texture significantly influence the observed creep anisotropy. We show that the elongated grain structure combined with grain boundary sliding plays a major role in the creep response, specifically in tilted specimens. KW - Additive manufactured Ni-base superalloys KW - Creep Anisotropy KW - Crystal plasticity PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-646884 DO - https://doi.org/10.1016/j.msea.2025.149029 VL - 945 SP - 1 EP - 15 PB - Elsevier B.V. AN - OPUS4-64688 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kianinejad, Kaveh A1 - Darvishi Kamachali, Reza A1 - Khedkar, Abhinav A1 - Manzoni, Anna Maria A1 - Agudo Jácome, Leonardo A1 - Schriever, Sina A1 - Saliwan Neumann, Romeo A1 - Megahed, Sandra A1 - Heinze, Christoph A1 - Kamrani, Sepideh A1 - Fedelich, Bernard T1 - Creep anisotropy of additively manufactured Inconel-738LC: Combined experiments and microstructure-based modeling N2 - The current lack of quantitative knowledge on processing-microstructure–property relationships is one of the major bottlenecks in today’s rapidly expanding field of additive manufacturing. This is centrally rooted in the nature of the processing, leading to complex microstructural features. Experimentally-guided modeling can offer reliable solutions for the safe application of additively manufactured materials. In this work, we combine a set of systematic experiments and modeling to address creep anisotropy and its correlation with microstructural characteristics in laser-based powder bed fusion (PBF-LB/M) additively manufactured Inconel-738LC (IN738LC). Three sample orientations (with the tensile axis parallel, perpendicular, and 45° tilted, relative to the building direction) are crept at 850 °C, accompanied by electron backscatter secondary diffraction (EBSD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations. A crystal plasticity (CP) model for Ni-base superalloys, capable of modeling different types of slip systems, is developed and combined with various polycrystalline representative volume elements (RVEs) built on the experimental measurements. Besides our experiments, we verify our modeling framework on electron beam powder bed fusion (PBF-EB/M) additively manufactured Inconel-738LC. The results of our simulations show that while the crystallographic texture alone cannot explain the observed creep anisotropy, the superlattice extrinsic stacking faults (SESF) and related microtwinning slip systems play major roles as active deformation mechanisms. We confirm this using TEM investigations, revealing evidence of SESFs in crept specimens. We also show that the elongated grain morphology can result in higher creep rates, especially in the specimens with a tilted tensile axis. KW - Additive manufactured Ni-base superalloys KW - Creep KW - Crystal plasticity KW - Superlattice extrinsic stacking faults PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-601576 DO - https://doi.org/10.1016/j.msea.2024.146690 SN - 0921-5093 VL - 907 SP - 1 EP - 16 PB - Elsevier B.V. AN - OPUS4-60157 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kindrachuk, Vitaliy A1 - Darvishi Kamachali, Reza T1 - Mean-field modeling and phase-field simulation of grain growth under directional driving forces N2 - Directional grain growth is a common phenomenon in the synthetic and natural evolution of various polycrystals. It occurs in the presence of an external driving force, such as a temperature gradient, along which grains show a preferred, yet competitive, growth. Novel additive manufacturing processes, with intense, localized energy deposition, are prominent examples of when directional grain growth can occur, beneath the melting pool. In this work, we derive a phenomenological mean-field model and perform 3D phase-field simulations to investigate the directional grain growth and its underlying physical mechanisms. The effect of the intensity of driving force is simulated and systematically analyzed at the evolving growth front as well as various cross-sections perpendicular to the direction of the driving force. We found that although the directional growth significantly deviates from normal grain growth, it is still governed by a power law relation α tⁿ with an exponent n ~ 0.6–0.7. The exponent n exhibits a nontrivial dependence on the magnitude of the directional driving force, such that the lowest growth exponent is observed for intermediate driving forces. We elaborate that this can originate from the fact that the forces at grain boundary junctions evolve out of balance under the influence of the directional driving force. With increasing the driving forces, the growth exponent asymptotically approaches a value of n ≈ 0.63, imposed by the largest possible grain aspect ratio for given grain boundary energies. The current combined mean-field and phase-field framework pave the way for future exploration in broader contexts such as the evolution of complex additively manufactured microstructures. KW - Additive manufacturing KW - Phase-field simulation KW - Grain growth KW - Mean-field modelling KW - Directional grain growth PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-593210 DO - https://doi.org/10.1016/j.mtla.2023.101989 SN - 2589-1529 VL - 33 SP - 1 EP - 10 PB - Elsevier AN - OPUS4-59321 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kindrachuk, Vitaliy A1 - Klunker, Andre T1 - Phase field modeling of Hertzian cone cracks under spherica indentation N2 - A phase field model of brittle fracture has been developed to simulate the Hertzian crack induced by penetration of a rigid sphere to an isotropic linear-elastic half-space. The fracture formation is regarded as a diffusive field variable, which is zero for the intact material and unity if there is a crack. Crack growth is assumed to be driven by a strain invariant. The numerical implementation is performed with the finite element method and an implicit time integration scheme. The mechanical equilibrium and the phase field equations are solved in a staggered manner, sequentially updating the displacement field and the phase field variable. Numerical examples demonstrate the capability of the model to reproduce the nucleation and growth of the Hertzian cone crack. KW - Hertzian cracks KW - Phase field model KW - Contact mechanics PY - 2021 DO - https://doi.org/10.1007/s11223-021-00251-9 VL - 52 IS - 6 SP - 967 EP - 974 AN - OPUS4-52276 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Li, L. A1 - Darvishi Kamachali, Reza A1 - Li, Z. A1 - Zhang, Z. T1 - Grain boundary energy effect on grain boundary segregation in an equiatomic high-entropy alloy N2 - Grain boundary (GB) Segregation has a substantial effect on the microstructure evolution and properties of polycrystalline alloys. The mechanism of nanoscale segregation at the various GBs in multicomponent alloys is of great challenge to reveal and remains elusive so far. To address this issue, we studied the GB segregation in a representative equiatomic FeMnNiCoCr high-entropy alloy (HEA) aged at 450 °C. By combining transmission Kikuchi diffraction, atom probe tomography analysis and a density-based thermodynamics modeling, we uncover the nanoscale segregation behavior at a series of well-characterized GBs of different characters. No segregation occurs at coherent twin boundaries; only slight nanoscale segregation of Ni takes place at the low-angle GBs and vicinal \Sigma 29b coincidence site lattice GBs. Ni and Mn show cosegregation of high levels at the general high-angle GBs with a strong depletion in Fe, Cr, and Co. Our density-based thermodynamic model reveals that the highly negative energy of mixing Ni and Mn is the main driving force for nanoscale cosegregation to the GBs. This is further assisted by the opposite segregation of Ni and Cr atoms with a positive enthalpy of mixing. It is also found that GBs of higher interfacial energy, possessing lower atomic densities (higher disorder and free volume), show higher segregation levels. By clarifying the origins of GB segregations in the FeMnNiCoCr HEA, the current work provides fundamental ideas on nanoscale segregation at crystal defects in multicomponent alloys. KW - Thermodynamics KW - High-Entropy Alloys KW - Grain Boundary Segregation PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-508827 DO - https://doi.org/10.1103/PhysRevMaterials.4.053603 VL - 4 IS - 5 SP - 053603 PB - American Physical Society AN - OPUS4-50882 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lin, Y.-Y. A1 - Schleifer, F. A1 - Holzinger, M. A1 - Ta, N. A1 - Skrotzki, Birgit A1 - Darvishi Kamachali, Reza A1 - Glatzel, U. A1 - Fleck, M. T1 - Quantitative Shape-Classification of Misfitting Precipitates during Cubic to Tetragonal Transformations: Phase-Field Simulations and Experiments N2 - The effectiveness of the mechanism of precipitation strengthening in metallic alloys depends on the shapes of the precipitates. Two different material systems are considered: tetragonal γ′′ precipitates in Ni-based alloys and tetragonal θ′ precipitates in Al-Cu-alloys. The shape formation and evolution of the tetragonally misfitting precipitates was investigated by means of experiments and phase-field simulations. We employed the method of invariant moments for the consistent shape quantification of precipitates obtained from the simulation as well as those obtained from the experiment. Two well-defined shape-quantities are proposed: (i) a generalized measure for the particles aspect ratio and (ii) the normalized λ2, as a measure for shape deviations from an ideal ellipse of the given aspect ratio. Considering the size dependence of the aspect ratio of γ′′ precipitates, we find good agreement between the simulation results and the experiment. Further, the precipitates’ in-plane shape is defined as the central 2D cut through the 3D particle in a plane normal to the tetragonal c-axes of the precipitate. The experimentally observed in-plane shapes of γ′′-precipitates can be quantitatively reproduced by the phase-field model. KW - γ″ phase KW - Phase-field simulation KW - Misfitting precipitate KW - Nickel-base alloy KW - Al-Cu alloy KW - θ′ phase KW - Precipitate shape PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-522743 DO - https://doi.org/10.3390/ma14061373 VL - 14 IS - 6 SP - 1373 PB - MDPI AN - OPUS4-52274 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Marschall, Niklas A1 - Murugan, Jegatheesan A1 - Darvishi Kamachali, Reza T1 - Incorporating elasticity into the thermodynamics and phase diagrams of multi-component systems N2 - Elastic energy plays a critical role in determining phase stability in compositionally complex alloys. However, quantifying elastic contributions in multi-component systems and incorporating them into phase diagram construction remain challenging. In this study, we present a generalized elastic energy formalism tailored for multi-component alloys, which can be directly and efficiently integrated with CALPHAD thermodynamic databases and existing frameworks such as Thermo-Calc (Andersson et al., 2002), Pandat (Cao et al., 2009) or FactSage (Bale et al., 2016). This elasticity formalism can also be introduced as a post-processing layer in open-source software such as pyCALPHAD (Otis and Liu, 2017) and Kawin (Ury et al., 2023) , enabling elastic assessments in multi-component systems. We apply our framework for constructing the phase diagram of quinary Fe–Mn–Ni–Co–Cu alloy system, utilizing convex hull and Hessian matrix under elastic considerations. Our results reveal that incorporating elastic energy leads to an expansion of both the spinodal region and the miscibility gap. These are governed by the intricate interplay of chemical and elastic driving forces: We found that Mn and Ni contribute strongly to chemical stabilization, while Cu and Co tend to destabilize the alloy, especially at low Mn concentrations. The stabilizing effect of Fe is also pronounced in Mn-deficient regions. Acting as a destabilizing factor, the elastic energy is primarily driven by the presence of Mn, underscoring its multifaceted role in thermodynamic stability. In Mn-rich compositions, Cu markedly reduces the elastic energy contribution. Combined with CALPHAD infrastructures, the current framework offers a practical pathway to improve the predictive accuracy of phase stability and transformations in complex multi-component alloys. KW - Elastic energy KW - HEA KW - CALPHAD KW - Elastic spinodal KW - Elastic miscibility gap KW - Elastic phase diagram PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-643339 DO - https://doi.org/10.1016/j.mtla.2025.102546 SN - 2589-1529 VL - 44 SP - 1 EP - 18 PB - Elsevier CY - Amsterdam, Niederlande AN - OPUS4-64333 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Murugan, Jegatheesan A1 - Darvishi Kamachali, Reza T1 - High‑throughput investigation of grain boundary segregation landscape in the Fe–Ni–Cr system N2 - Understanding phase stability in multicomponent alloy systems, particularly at internal interfaces, remains a major challenge in materials science. Grain boundary (co-)segregation is a critical factor influencing interfacial stability, often leading to microstructural degradation and safety concerns. In this study, we investigate segregation behavior in the face-centered cubic (FCC) Fe–Ni–Cr alloy system, a foundational system for many steels, superalloys, and high-entropy alloys. CALPHAD-integrated density-based phase-field model is extended to compute the segregation of Fe, Ni, and Cr at grain boundaries as a function of the bulk composition, with the relative GB density serving as a key parameter representing grain boundary character. A high-throughput computational screening is performed across the stable compositional space at 723 K, 1023 K, and 1323 K. The results reveal a rich and temperature-sensitive segregation landscape, with element-specific enrichment and depletion patterns that vary with alloy composition. Notably, opposite segregation trends between Ni and Cr, and frequent co-segregation of Fe and Ni, are observed at lower temperatures. The developed framework captures the coupled effects of temperature, chemical interactions, grain boundary structure, and enthalpy-entropy compensation on segregation and GB phase stability. The origin and implications of these phenomena are discussed in terms of the underlying thermodynamic driving forces. KW - Segregation Engineering KW - Grain boundary segregation KW - Thermodynamics KW - CALPHAD KW - Fe--Ni--Cr alloys PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-646404 DO - https://doi.org/10.1007/s10853-025-11717-5 SN - 1573-4803 SP - 1 EP - 21 PB - Springer Science + Business Media CY - Dordrecht [u.a.] AN - OPUS4-64640 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rockenhäuser, Christian A1 - Rowolt, C. A1 - Milkereit, B. A1 - Darvishi Kamachali, Reza A1 - Kessler, O. A1 - Skrotzki, Birgit T1 - On the long-term aging of S-phase in aluminum alloy 2618A N2 - The aluminum alloy 2618A is applied for engine components such as radial compressor wheels which operate for long time at elevated temperatures. This results in coarsening of the hardening precipitates and degradation in mechanical properties during the long-term operation, which is not taken into account in the current lifetime prediction models due to the lack of quantitative microstructural and mechanical data. To address this issue, a quantitative investigation on the evolution of precipitates during long-term aging at 190 °C for up to 25,000 h was conducted. Detailed transmission electron microscopy (TEM) was combined with Brinell hardness measurements and thorough differential scanning calorimetry (DSC) experiments. The results showthat GPB zones and S-phase Al2CuMg grow up to < 1,000 h during which the GPB zones dissolve and S-phase precipitates form. For longer aging times, only S-phase precipitates coarsen, which can be well described using the Lifshitz–Slyozov Wagner theory of ripening. A thorough understanding of the underlying microstructural processes is a prerequisite to enable the integration of aging behavior into the established lifetime models for components manufactured from alloy 2618A. KW - Long-term aging KW - Transmission electron microscopy (TEM) KW - Differential scanning calorimetry (DSC) KW - Microstructure KW - S-phase KW - Ostwald ripening PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-519899 DO - https://doi.org/10.1007/s10853-020-05740-x SN - 0022-2461 VL - 56 IS - 14 SP - 8704 EP - 8716 PB - Springer Nature AN - OPUS4-51989 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rosenbusch, Sjard Mathis A1 - Diercks, Philipp A1 - Kindrachuk, Vitaliy A1 - Unger, Jörg F. T1 - Integrating custom constitutive models into FEniCSx: A versatile approach and case studies N2 - The development and integration of user-defined constitutive relationships into finite element (FE) tools using standardized interfaces play a pivotal role in advancing the capabilities of FE solvers for structural mechanics applications. While commercial FE solvers like Abaqus and Ansys have designed their interfaces to provide custom stresses, tangents, and updated history variables, the open-source solver FEniCSx remains efficient only when the constitutive update has an analytical representation. This restricts the application of FEniCSx for non-linear structural mechanics. Since FEniCSx has become a powerful and popular open-source tool for solving partial differential equations, particularly due to its automatic computation of Hessians, we aim to develop a generalized interface to enhance its capability for constitutive modeling. This approach will address complex constitutive equations that require iterative solutions at the quadrature point level. Specific implementation challenges, such as using return-mapping procedures, can then be managed commonly. The provided interface for custom constitutive models offers a versatile way to implement them in various languages, including C++, Python, Rust, and Fortran. Finally, with UMATs for viscoplastic models as an example, we demonstrate how existing user subroutines can be incorporated into the interface and utilized within the FEniCSx framework. KW - Finite element method KW - Constitutive models KW - FEniCSx KW - UMAT KW - Rust KW - Python KW - C++ PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-630439 DO - https://doi.org/10.1016/j.advengsoft.2025.103922 SN - 0965-9978 VL - 206 SP - 1 EP - 11 PB - Elsevier CY - Amsterdam AN - OPUS4-63043 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ruffini, A. A1 - Le Bouar, Y. A1 - Finel, A. A1 - Epishin, A. I. A1 - Fedelich, Bernard A1 - Feldmann, Titus A1 - Viguier, B. A1 - Poquillon, D. T1 - Dislocations interacting with a pore in an elastically anisotropic single crystal nickel-base superalloy during hot isostatic pressing N2 - The formation of pores in CMSX-4 nickel based superalloys is detrimental to the service life of the material. A way to avoid the problem is to treat the superalloys under Hot Isostatic Pressing (HIP), which enables a large volume fraction of pores to be annihilated. This paper aims to understand the contribution of plastic activity related to the gliding of dislocations on the pore annihilation. Simulations based on a phase-field model of dislocation are performed and make it possible to consider the strong anisotropy of the CMSX-4 under HIP conditions in conjunction to the strong elastic heterogeneity introduced by the pore. For pores with a radius of few micrometers, it is shown that edge parts of dislocation lines that present an extra half atomic plane oriented towards the pore are stacked above and under it in the direction which is perpendicular to their slip-planes, causing an increase of the number of dislocation along the four octahedral directions of the FCC single crystal which intersect the pore center. Results are streamlined within the isotropic elastic theory of dislocations. Effects of elastic anisotropy and dislocation reactions are also investigated in order to specify what would be the dislocation configuration around a pore in CMSX-4 under HIP conditions. Notably, the elastic anisotropy is shown to significantly modify the arrangement of dislocations close to the pore equator. Simulations also allow for the characterization of pore/dislocation interactions when dislocations are involved in Low Angle Boundaries as experimentally observed. KW - HIP KW - Superalloys KW - Dislocation KW - Pore KW - Phase-field PY - 2022 DO - https://doi.org/10.1016/j.commatsci.2021.111118 SN - 0927-0256 VL - 204 SP - 1 EP - 14 PB - Elsevier CY - Amsterdam AN - OPUS4-54220 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schilling, Markus A1 - Marschall, Niklas A1 - Niebergall, Ute A1 - Böhning, Martin T1 - Modernizing FNCT data handling in polymer labs: Towards efficient management N2 - A streamlined Python-based workflow for transforming Full-Notch Creep Test (FNCT) data into organized, machine-actionable formats is presented. The workflow automates the conversion of raw FNCT data from classic CSV and Excel files into structured outputs that facilitate future semantic integration. Emphasizing practical data handling, the approach includes automation scripts for efficient data extraction, transformation, and storage, which culminate in well-ordered files. This transformation paves the way for potential semantic data integration and facilitates access for users with varying levels of digital experience to enhanced data management in polymer research and testing. KW - PE-HD KW - Full-Notch Creep Test (FNCT) KW - Environmental Stress Cracking (ESC) KW - Data Interoperability KW - FAIR Data KW - Semantic Data PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-637826 DO - https://doi.org/10.1016/j.commatsci.2025.114085 SN - 0927-0256 VL - 259 SP - 1 EP - 5 PB - Elsevier B.V. AN - OPUS4-63782 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schilling, Markus A1 - Marschall, Niklas A1 - Niebergall, Ute A1 - Wachtendorf, Volker A1 - Böhning, Martin T1 - Characteristics of environmental stress cracking of PE-HD induced by biodiesel and diesel fuels N2 - In the context of the increasing effect of carbon dioxide emissions on the global climate biodiesel produced from renewable sources has emerged as a promising contender replacing fossil fuels, especially in long-range transport vehicles, using existing engines and infrastructure. High-density polyethylene is one of the prevailing materials for pipe and container applications for storage and transport of such fuels, both, from fossil and renewable resources. The contact with the respective fuels raises questions concerning material compatibility as biodiesel exhibits significant differences compared to conventional diesel fuel affecting its sorption and plasticization behavior in polyethylene. In this study, its behavior with respect to environmental stress cracking, considered one of the most frequent damage mechanisms leading to failure of polymer parts and packaging, was evaluated using the well-established Full Notch Creep Test. This approach allows for a detailed fracture surface analysis using imaging techniques, such as optical and laser scanning microscopy, as well as infrared spectroscopy. Comparing the environmental stress cracking behavior in standard surfactant solutions with that in biodiesel and diesel, respective crack propagation rates, showing different levels of acceleration, were determined and details of the underlying mechanisms could be revealed. Furthermore, the specific infrared absorption of the biodiesel’s ester functionality allows its semi-quantitative determination on the fracture surface of the tested specimens after failure. Thus, a preferred uptake of sorptive fluids in the fracture zone due to local morphological changes of the polyethylene could be directly evidenced by infrared spectroscopy. KW - Environmental stress cracking (ESC) KW - Full notch creep test (FNCT) KW - Confocal laser scanning microscopy (LSM) KW - Biodiesel KW - Diesel PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-608591 DO - https://doi.org/10.1016/j.polymertesting.2024.108547 SN - 0142-9418 VL - 138 SP - 1 EP - 16 PB - Elsevier Ltd. AN - OPUS4-60859 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schilling, Markus A1 - Marschall, Niklas A1 - Niebergall, Ute A1 - Wachtendorf, Volker A1 - Böhning, Martin T1 - Unveiling Effects of Biodiesel and Diesel on Environmental Stress Cracking of PE-HD N2 - The behavior of high‐density polyethylene with respect to resistance against environmental stress cracking (ESC) is usually regarded as an inherent material property being specific for respective types of PE‐HD and tested using standardized methods, conditions, and also standard testing liquids (usually aqueous surfactant solutions). On the other hand, for practical applications the ESC behavior of those polymeric materials, commonly used for pipes or containers, in contact with other liquids (e.g., fuels) is often of relevant interest, but for a reasonable assessment, where consistent benchmark data for a direct comparison are often missing, it is essential to determine the actually prevailing failure mode and classify it related to crack propagation or other mechanisms. Using the well‐established Full Notch Creep Test, which favorably allows for a detailed microscopic fracture surface analysis after failure, the behavior of two typical PE‐HD types for container applications is investigated in biodiesel and diesel and compared to a standard surfactant solution. This enables a clear identification of characteristic features of the interaction of biodiesel and diesel as sorptive fuels in contact with the polymer, revealing the complex interplay of sorption and plasticization as well as ESC inducing effects on PE‐HD, which could be clearly shown for both fuels. KW - Biodiesel KW - Confocal laser scanning microscopy (LSM) KW - Diesel KW - Full notch creep test (FNCT) KW - Plasticization PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-650525 DO - https://doi.org/10.1002/pen.70239 SN - 0032-3888 SP - 1 EP - 16 PB - Wiley CY - Hoboken (NJ) AN - OPUS4-65052 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schilling, Markus A1 - Niebergall, Ute A1 - Marschall, Niklas A1 - Alig, I. A1 - Böhning, Martin T1 - A phenomenological criterion for an optical assessment of PE-HD fracture surfaces obtained from FNCT N2 - The full-notch creep test (FNCT) is a common test method to evaluate the environmental stress cracking (ESC) behavior of high-density polyethylene (PE-HD), e.g. for container materials. The test procedure as specified in ISO 16770 provides a comparative measure of the resistance against ESC using the time to failure of PE-HD specimens under constant mechanical load in a well-defined liquid test environment. Since the craze-crack damage mechanism underlying the ESC phenomenon is associated with brittle failure, the occurrence of a predominantly brittle fracture surface is a prerequisite to consider an FNCT measurement as representative for ESC, i.e. a time to failure dominated by craze-crack propagation. The craze-crack propagation continuously reduces the effective residual cross-sectional area of the specimen during the test, which results in a corresponding increase of the effective mechanical stress. Thus, a transition to ductile shear deformation is inevitable at later stages of the test, leading usually to a pronounced central ligament. Therefore, an optical evaluation of FNCT fracture surfaces concerning their brittleness is essential. An enhanced imaging analysis of FNCT fracture surfaces enables a detailed assessment of craze-crack Propagation during ESC. In this study, laser scanning microscopy (LSM) was employed to evaluate whether FNCT fracture surfaces are representative with respect to craze-crack propagation and ESC. Based on LSM height data, a phenomenological criterion is proposed to assess the validity of distinct FNCT measurements. This criterion is supposed to facilitate a quick evaluation of FNCT results in practical routine testing. Its applicability is verified on a sample basis for seven different commercial PE-HD container materials. KW - Environmental stress cracking (ESC) KW - Full notch creep test (FNCT) KW - Laser scanning microscopy (LSM) KW - Fracture surfaces KW - Optical criterion of brittleness PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-521012 DO - https://doi.org/10.1016/j.polymertesting.2020.107002 VL - 94 SP - 107002 PB - Elsevier Ltd. CY - Amsterdam AN - OPUS4-52101 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schilling, Markus A1 - Niebergall, Ute A1 - Marschall, Niklas A1 - Meinel, Dietmar A1 - Böhning, Martin T1 - Relation of craze to crack length during slow crack growth phenomena in high‐density polyethylene N2 - The craze‐crack mechanism occurring in high‐density polyethylene (HDPE) causing slow crack growth and environmental stress cracking is investigated in detail with respect to the relation of crack length and the related craze zone. This is essential for the understanding of the resulting features of the formed fracture surface and their interpretation in the context of the transition from crack propagation to ductile shear deformation. It turns out that an already formed craze zone does not inevitably result in formation of a propagating crack, but could also undergo ductile failure. For the examination, the full notch creep test (FNCT) was employed with a subsequent advanced fracture surface analysis that was performed using various imaging techniques: light microscopy, laser scanning microscopy, scanning electron microscopy, and X‐ray micro computed tomography scan. FNCT specimens were progressively damaged for increasing durations under standard test conditions applying Arkopal, the standard surfactant solution, and biodiesel as test media were used to analyze the stepwise growth of cracks and crazes. From considerations based on well‐established fracture mechanics approaches, a theoretical correlation between the length of the actual crack and the length of the preceding craze zone was established that could be evidenced and affirmed by FNCT fracture surface analysis. Moreover, the yield strength of a HDPE material exposed to a certain medium as detected by a classic tensile test was found to be the crucial value of true stress to induce the transition from crack propagation due to the craze‐crack mechanism to shear deformation during FNCT measurements. Highlights - Progress of crack formation in high‐density polyethylene is analyzed by different imaging techniques - Determined growth rates depend on distinction between craze zone and crack - The ratio of the present crack to the anteceding craze zone is validated theoretically - The transition from crack propagation to ductile shear deformation is identified - An already formed craze zone may still fail by ductile mechanisms KW - Craze-crack mechanism KW - Environmental stress cracking (ESC) KW - Full notch creep test (FNCT) KW - Laser scanning microscopy (LSM) KW - Slow crack growth (SCG) KW - X-ray computed tomography (CT) PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-601831 DO - https://doi.org/10.1002/pen.26698 SN - 1548-2634 VL - 64 IS - 6 SP - 2387 EP - 2403 PB - Wiley AN - OPUS4-60183 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stargardt, Patrick A1 - Bresch, Sophie A1 - Falkenberg, Rainer A1 - Mieller, Björn T1 - Effect of Reaction Layers on Internal Stresses in Co‐Fired Multilayers of Calcium Manganate and Calcium Cobaltite N2 - A widespread recovery of waste heat requires a cost‐effective production of thermoelectric generators. Thermoelectric oxides are predestined for use at high temperatures. For manufacturing reasons, a multilayer generator design will be easily scalable and cost‐effective. To evaluate the potential of ceramic multilayer technology for that purpose, a multilayer of the promising thermoelectric oxides calcium cobaltite (Ca3Co4O9), calcium manganate (CMO, CaMnO3), and glass–ceramic insulation layers is fabricated. Cracks and reaction layers at the interfaces are observed in the microstructure. The compositions of these reaction layers are identified by energy‐dispersive X‐ray spectroscopy and X‐ray diffraction. Mechanical and thermal properties of all layers are compiled from literature or determined by purposeful sample preparation and testing. Based on this data set, the internal stresses in the multilayer after co‐firing are calculated numerically. It is shown that tensile stresses in the range of 50 MPa occur in the CMO layers. The reaction layers have only a minor influence on the level of these residual stresses. Herein, it is proven that the material system is basically suitable for multilayer generator production, but that the co‐firing process and the layer structure must be adapted to improve densification and reduce the tensile stresses in the CMO. KW - Ceramic multilayers KW - Co-firings KW - Internal stresses PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-601626 DO - https://doi.org/10.1002/pssa.202300956 SP - 1 EP - 9 PB - Wiley VHC-Verlag AN - OPUS4-60162 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Suárez Ocano, Patricia A1 - Agudo Jácome, Leonardo A1 - Lopez-Galilea, I. A1 - Darvishi Kamachali, Reza A1 - Fries, S. G. T1 - Data regarding the experimental findings compared with CALPHAD calculations of the AlMo0.5NbTa0.5TiZr refractory high entropy superalloy N2 - This contribution contains the raw data used to compare experimental results with thermodynamic calculations using the CALPHAD method, which is related to the research article “The AlMo0.5NbTa0.5TiZr refractory high entropy superalloy: experimental findings and comparison with calculations using the CALPHAD method” [1] , and therefore this article can be used as a basis for interpreting the data contained therein. The AlMo0.5NbTa0.5TiZr refractory superalloy was characterized in the cast and annealed condition (1400 °C for 24 h) in order to measure grain size and to identify and measure the size and area fraction of the phases present. The raw data of this article include X-ray diffraction (XRD) measurements, microstructural characterization by scanning and transmission electron microscopy (SEM and TEM), and elemental analysis by energy dispersive X-ray spectroscopy (EDX). XRD includes the determination of phases and the lattice parameters (A2, B2, and hexagonal structure). Microstructural analysis by scanning and transmission electron microscopy includes (1) identification of composition, size, and volume fraction of the present phases and (2) determination of grain size. Based on these experimental data, it is possible to identify similarities and discrepancies with the data calculated using the CALPHAD method for the alloy under study in Ref. [1] , which provides the basis for better and more efficient development of reliable databases. KW - Transmission electron microscopy KW - Scanning electron microscopy KW - Microstructural characterization KW - Refractory high entropy alloys PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-568009 DO - https://doi.org/10.1016/j.dib.2022.108858 SN - 2352-3409 VL - 46 SP - 1 EP - 19 PB - Elsevier CY - Amsterdam AN - OPUS4-56800 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Suárez Ocano, Patricia A1 - Fries, S. G. A1 - Lopez-Galilea, I. A1 - Darvishi Kamachali, Reza A1 - Roik, J. A1 - Agudo Jácome, Leonardo T1 - The AlMo0.5NbTa0.5TiZr refractory high entropy superalloy: Experimental findings and comparison with calculations using the CALPHAD method N2 - Detailed microstructural characterization of the AlMo0.5NbTa0.5TiZr refractory high entropy superalloy in the as-cast state is reported for first time and compared with the state annealed at 1400 oC for 24 h. The former shows a dendritic structure, with a mixture of A2/B2 phases < 20 nm in both the dendritic and interdendritic regions. A mostly amorphous phase, rich in Al and Zr, is found within the interdendritic region. The annealed state reproduced the combination of A2/B2/Al-Zr-rich phases reported previously. Calculations from two relevant ThermoCalc databases were compared with the experimental results. Equilibrium calculations were compared with results for the annealed alloy, whereas solidification paths calculated using Scheil-Gulliver model were used for comparison with the as-cast alloy. A previously hypothesized spinodal decomposition during cooling as the mechanism responsible for the patterned A2/B2 microstructure is confirmed via the CALPHAD calculations, pointing to its use as an efficient design tool for such alloys. Finally, the comparison between the experimental and computational findings allowed better understanding the solidification path and equilibrium stability of this alloy, giving a base to make better decisions on the field of new refractory superalloy design. KW - CALPHAD database analysis KW - Refractory superalloys KW - Chemically complex alloy KW - Characterization KW - Microstructure PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-545906 DO - https://doi.org/10.1016/j.matdes.2022.110593 SN - 1873-4197 VL - 217 SP - 1 EP - 13 PB - Elsevier CY - Amsterdam AN - OPUS4-54590 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ta, N. A1 - Bilal, M. U. A1 - Häusler, I. A1 - Saxena, A. A1 - Lin, Y.-Y. A1 - Schleifer, F. A1 - Fleck, M. A1 - Glatzel, U. A1 - Skrotzki, Birgit A1 - Darvishi Kamachali, Reza T1 - Simulation of the θ′ Precipitation Process with Interfacial Anisotropy Effects in Al-Cu Alloys N2 - The effects of anisotropic interfacial properties and heterogeneous elasticity on the growth and ripening of plate-like θ′-phase (Al2Cu) in Al-1.69 at.% Cu alloy are studied. Multi-phase-field simulations are conducted and discussed in comparison with aging experiments. The precipitate/matrix interface is considered to be anisotropic in terms of its energy and mobility. We find that the additional incorporation of an anisotropic interfacial mobility in conjunction with the elastic anisotropy result in substantially larger aspect ratios of the precipitates closer to the experimental observations. The anisotropy of the interfacial energy shows comparably small effect on the precipitate’s aspect ratio but changes the interface’s shape at the rim. The effect of the chemo-mechanical coupling, i.e., the composition dependence of the elastic constants, is studied as well. We show that the inverse ripening phenomenon, recently evidenced for δ’ precipitates in Al-Li alloys (Park et al. Sci. Rep. 2019, 9, 3981), does not establish for the θ′ precipitates. This is because of the anisotropic stress fields built around the θ′ precipitates, stemming from the precipitate’s shape and the interaction among different variants of the θ′ precipitate, that disturb the chemo-mechanical effects. These results show that the chemo-mechanical effects on the precipitation ripening strongly depend on the degree of sphericity and elastic isotropy of the precipitate and matrix phases. KW - Aging KW - Phase-field simulation KW - Interfacial anisotropy KW - Chemo-mechanical coupling KW - Precipitation KW - Elasticity KW - θ′-(Al2Cu) precipitate phase PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-522672 DO - https://doi.org/10.3390/ma14051280 VL - 14 IS - 5 SP - 1280 PB - MDPI AN - OPUS4-52267 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -