@misc{GrudininBleykherKrivobokovetal., author = {Grudinin, V. A. and Bleykher, G. A. and Krivobokov, V. P. and Semyonov, O. V. and Obrosov, Aleksei and Weiß, Sabine and Sidelev, D. V.}, title = {Hot target magnetron sputtering enhanced by RF-ICP source: Microstructure and functional properties of CrNx coatings}, series = {Vacuum}, volume = {200}, journal = {Vacuum}, issn = {1879-2715}, doi = {10.1016/j.vacuum.2022.111020}, abstract = {CrNx coatings were deposited at high rates (100-130 nm/min) using hot Cr target magnetron sputtering enhanced by a radio-frequency inductively coupled plasma (RF-ICP) source in an Ar + N2 atmosphere. Besides separation of inert and reactive atmosphere, the RF-ICP source can be an effective tool for ion assistance in case of coating growth and to tailor film parameters. The effects of nitrogen flow rate and substrate bias potential on microstructure and functional properties of the CrNx coatings were investigated. An increase in nitrogen flow rate favored the formation of a looser microstructure of the coatings, while substrate biasing had the opposite effect. The functional properties were strongly dependent on the phase composition of the CrNx coatings. The change in coating microstructure significantly affected hardness, elastic modulus, adhesion, friction coefficients and corrosion resistance. The results indicated that ion assistance can be a key feature for regulating functional properties in the considered type of coating deposition. Cr2N and CrN compound coatings with high hardness (∼20 GPa) and low corrosion current density (icorr ∼ 3-5·10-9 A/cm2) in a 3.5 wt\% NaCl solution were obtained by high-rate deposition.}, language = {en} } @misc{AlontsevaSafarovaYantsenVoinarovychetal., author = {Alontseva, Darya and Safarova (Yantsen), Yuliya and Voinarovych, Sergii and Obrosov, Aleksei and Yamanoglu, Ridvan and Khoshnaw, Fuad and Yavuz, Hasan Ismail and Nessipbekova, Assem and Syzdykova, Aizhan and Azamatov, Bagdat and Khozhanov, Alexandr and Weiß, Sabine}, title = {Biocompatibility and Corrosion of Microplasma-Sprayed Titanium and Tantalum Coatings versus Titanium Alloy}, series = {Coatings}, volume = {14}, journal = {Coatings}, number = {2}, issn = {2079-6412}, doi = {10.3390/coatings14020206}, abstract = {This study investigates the in vitro biocompatibility, corrosion resistance, and adhesion strength of a gas abrasive-treated Ti6Al4V alloy, alongside microplasma-sprayed titanium and tantalum coatings. Employing a novel approach in selecting microplasma spray parameters, this study successfully engineers coatings with tailored porosity, roughness, and over 20\% porosity with pore sizes up to 200 μm, aiming to enhance bone in-growth and implant integration. This study introduces an innovative methodology for quantifying surface roughness using laser electron microscopy and scanning electron microscopy, facilitating detailed morphological analysis of both the substrate and coatings. Extensive evaluations, including tests for in vitro biocompatibility, corrosion resistance, and adhesive strength, revealed that all three materials are biocompatible, with tantalum coatings exhibiting superior cell proliferation and osteogenic differentiation, as well as the highest corrosion resistance. Titanium coatings followed closely, demonstrating favorable osteogenic properties and enhanced roughness, which is crucial for cell behavior and attachment. These coatings also displayed superior tensile adhesive strengths (27.6 ± 0.9 MPa for Ti and 28.0 ± 4.9 MPa for Ta), surpassing the ISO 13179-1 standard and indicating a robust bond with the substrate. Our findings offer significant advancements in biomaterials for medical implants, introducing microplasma spraying as a versatile tool for customizing implant coatings, particularly emphasizing the superior performance of tantalum coatings in terms of biocompatibility, osteogenic potential, and corrosion resistance. This suggests that tantalum coatings are a promising alternative for enhancing the performance of metal implants, especially in applications demanding high biocompatibility and corrosion resistance.}, language = {en} } @misc{FellahHezilBourasetal., author = {Fellah, Mamoun and Hezil, Naouel and Bouras, Dikra and Bouchareb, Nabila and Larios, Alejandro Perez and Obrosov, Aleksei and El-Hiti, Gamal A. and Weiß, Sabine}, title = {Investigating the effect of Zr content on electrochemical and tribological properties of newly developed near β-type Ti-alloys (Ti-25Nb-xZr) for biomedical applications}, series = {Journal of Science: Advanced Materials and Devices}, journal = {Journal of Science: Advanced Materials and Devices}, issn = {2468-2179}, doi = {10.1016/j.jsamd.2024.100695}, abstract = {In order to create alloys with exceptional properties for orthopedic uses, this study focuses on the impact of zirconium (Zr) content on the structural, electrochemical, and tribological qualities of nanostructured Ti-25Nb-xZr [x = 5, 10, 15, 20, 25, and 30 atomic (at.) \%] alloys. The structural evolution was investigated using XRD and SEM techniques. The mechanical characteristics of the produced alloys, including Vickers hardness and Young's modulus, were measured. In addition, the corrosion tests were performed using the OCP, EIS, and PD methods in Ringer's solution within the independent pH range at 37 °C. A ball-on-disc tribometer was used to investigate the tribological behavior of the alloys under various loads and wet conditions using the Ringer solution. It has been verified that Zr content (at. \%) in the alloys had an impact on their morphologies, structural evolution, and mechanical characteristics. According to the morphological analysis, the particle and crystallite size decreases with increasing Zr content. Young's modulus and Vickers hardness show the same tendency. The EIS data demonstrated that a single passive film formed on the alloy surfaces, and the addition of Zr enhanced the corrosion resistance of the passive films. The polarization curves demonstrate that the alloys had low corrosion current densities and large passive areas without the passive films disintegrating. Likewise, the inclusion of Zr resulted in a reduction in the corrosion and passive current densities values. All of these results suggested that the titanium alloys exhibit a more noble electrochemical activity caused by Zr. From the tribological perspective, it was found that the friction coefficient of the alloys reduced with increasing Zr content.}, language = {en} } @misc{FellahBoucharebHeziletal., author = {Fellah, Mamoun and Bouchareb, Nabila and Hezil, Naouel and Merah, Ne{\c{c}}ar and Alashkar, Yasser and Imran, Mohd and Obrosov, Aleksei and Weiß, Sabine}, title = {Electrochemical analysis of mechanically alloyed Ti50\%-Ni50\% alloy for bone implants use}, series = {Journal of Alloys and Compounds}, journal = {Journal of Alloys and Compounds}, number = {1010}, issn = {1873-4669}, doi = {https://doi.org/10.1016/j.jallcom.2024.178046}, pages = {1 -- 13}, abstract = {The corrosion resistance of an implant material is an essential element of its biocompatibility. This research focuses on studying the effect of grinding/milling time on the corrosion behavior of the mechanically alloyed Ti50 \%-Ni50 \% (at\%) alloy, for bone implant use, at varying milling times of 2, 6, 12, and 18 h. The powder particles' size, shape, and homogeneous chemical content were examined employing scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The alloyed particles' structural characteristics were determined by X-ray diffraction (XRD). Moreover, the characterization of the electrochemical properties was performed utilizing open-circuit potential (OCP) measurement, the Potentiodynamic Polarization (PD), and the Electrochemical Impedance Spectroscopy (EIS) technique. Electrochemical tests were conducted in physiological mediums simulating the human body: Hank's solution. The results revealed that; as the grinding time increased the crystallite size reduced from 57 nm to 29 nm, whereas the lattice parameters increased slightly from 3.18 to 3.22 {\AA}, while the microstrain increased from 0.32 \% to 0.99 \%. Moreover, the hardness and Young's Modulus increased by about 70 and 16 \%, respectively with milling period going from 2 to 18 h. The findings of the electrochemical test demonstrated that as milling progressed, corrosion resistance increased. The evolution of OCP curves as a function of the duration of immersions indicated that OCP increased with the duration of immersion up to 2500 s; this is due to a stable passive layer that has formed on the samples' surface. The results of potentiodynamic polarization curves revealed that both corrosion current density (icorr) and corrosion rate (CR) decreased reaching a value of 3.6945E-07 A/cm2 and 0.0074722 mm/year, respectively, at longer milling time (18 h). While, corrosion potential (Ecorr) increased from -0.51255 V/SCE to -0.29997 V/SCE with increasing grinding time. Additionally, the EIS data indicated that the resistance of the passive film increased with increasing milling times. The samples of Ti50-Ni50 produced at longer milling time exhibited excellent corrosion resistance due to the formation of a stable passive film which makes them useful for bone implants.}, language = {en} } @misc{AlontsevaSafarovaYantsenVoinarovychetal., author = {Alontseva, Darya and Safarova (Yantsen), Yuliya and Voinarovych, Sergii and Obrosov, Aleksei and Yamanoglu, Ridvan and Khoshnaw, Fuad and Nessipbekova, Assem and Syzdykova, Aizhan and Yavuz, Hasan Ismail and Kaliuzhnyi, Sergii and Krasavin, Alexander and Azamatov, Bagdat and Khozhanov, Alexandr and Olzhayev, Farkhad and Weiß, Sabine}, title = {Microplasma-Sprayed Titanium and Hydroxyapatite Coatings on Ti6Al4V Alloy: in vitro Biocompatibility and Corrosion Resistance: Part I}, series = {Johnson Matthey Technology Review}, volume = {69}, journal = {Johnson Matthey Technology Review}, number = {1}, doi = {10.1595/205651325X17201903387613}, pages = {45 -- 58}, abstract = {This two-part paper investigates the bioactivity and mechanical properties of coatings applied to Ti6Al4V, a common titanium alloy used in endoprosthetic implants. Coatings made from hydroxyapatite (HA) powder and commercially pure titanium (CP-Ti) wires were applied using microplasma spraying. The study focuses on the responses of rat mesenchymal stem cells (MSCs), which are essential for bone healing, to these coatings. Part I shows how adjusting the microplasma spraying process allows coatings with varying porosity and surface roughness to be achieved.}, language = {en} } @misc{AlontsevaSafarovaYantsenVoinarovychetal., author = {Alontseva, Darya and Safarova (Yantsen), Yuliya and Voinarovych, Sergii and Obrosov, Aleksei and Yamanoglu, Ridvan and Khoshnaw, Fuad and Nessipbekova, Assem and Syzdykova, Aizhan and Yavuz, Hasan Ismail and Kaliuzhnyi, Sergii and Krasavin, Alexander and Azamatov, Bagdat and Khozhanov, Alexandr and Olzhayev, Farkhad and Weiß, Sabine}, title = {Microplasma-sprayed titanium and hydroxyapatite coatings on Ti6Al4V alloy: in vitro biocompatibility and corrosion resistance : part II coatings enhance cell proliferation, corrosion resistance and implant integration}, series = {Johnson Matthey Technology Review}, volume = {69 (2025)}, journal = {Johnson Matthey Technology Review}, number = {1}, issn = {2056-5135}, doi = {10.1595/205651325X17290035905758}, pages = {59 -- 75}, abstract = {Part II presents the results which show that HA coatings significantly enhance MSC proliferation by 13\% compared to the titanium alloy base, while titanium coatings also exhibit an 11\% increase. Porosity inversely affects CP-Ti's elasticity. Coatings with lower porosity demonstrate better corrosion resistance. HA coatings promote osteogenic activity and angiogenesis, which is crucial for implant integration.}, language = {en} } @misc{SynodinosKarnatakAguilar‐Triguerosetal., author = {Synodinos, Alexis D. and Karnatak, Rajat and Aguilar-Trigueros, Carlos A. and Gras, Pierre and Heger, Tina and Ionescu, Danny and Maaß, Stefanie and Musseau, Camille L. and Onandia, Gabriela and Planillo, Aimara and Weiss, Lina and Wollrab, Sabine and Ryo, Masahiro}, title = {The rate of environmental change as an important driver across scales in ecology}, series = {Oikos}, volume = {2023}, journal = {Oikos}, number = {4}, publisher = {Wiley}, issn = {0030-1299}, doi = {10.1111/oik.09616}, pages = {11}, abstract = {Global change has been predominantly studied from the prism of 'how much' rather than 'how fast' change occurs. Associated to this, there has been a focus on environmental drivers crossing a critical value and causing so-called regime shifts. This presupposes that the rate at which environmental conditions change is slow enough to allow the ecological entity to remain close to a stable attractor (e.g. an equilibrium). However, environmental change is occurring at unprecedented rates. Equivalently to the classical regime shifts, theory shows that a critical threshold in rates of change can exist, which can cause rate-induced tipping (R-tipping). However, the potential implications of R-tipping in ecology remain understudied. We aim to facilitate the application of R-tipping theory in ecology with the objective of identifying which properties (e.g. level of organisation) increase susceptibility to rates of change. First, we clarify the fundamental difference between tipping caused by the magnitude as opposed to the rate of change crossing a threshold. Then we present examples of R-tipping from the ecological literature and seek the ecological properties related to higher sensitivity to rates of change. Specifically, we consider the role of the level of ecological organisation, spatial processes, eco-evolutionary dynamics and pair-wise interactions in mediating or buffering rate-induced transitions. Finally, we discuss how targeted experiments can investigate the mechanisms associated to increasing rates of change. Ultimately, we seek to highlight the need to better understand how rates of environmental change may induce ecological responses and to facilitate the systematic study of rates of environmental change in the context of current global change.}, language = {en} } @misc{YangWeiss, author = {Yang, Yitong and Weiß, Sabine}, title = {In-situ investigation on cyclic bending deformation of oligocrystalline 316LVM steel for coronary stent application with EBSD}, series = {International Conference on Strength of Materials 2022}, journal = {International Conference on Strength of Materials 2022}, publisher = {HAL open science}, pages = {9}, abstract = {The objective of this work is to investigate the strain localization and slip activation of the microstructure of oligo-crystalline 316LVM steel struts evolving during different cyclic bending deformation stages (number of cycles) and loading conditions (maximum stress and neutral). A micro-scale three-point bending fixture was designed and incorporated into a micro tensile/compression machine inside a scanning electron microscope (SEM) to perform in-situ electron backscatter diffraction (EBSD) measurements during different phases of cyclic fatigue testing. The following results were obtained: 1) The quantitative strain could be compared after each stage of deformation. 2) The rotation of the grains orientations is observed during the cyclic deformation while the morphology did not change significantly. The results contribute to the understanding of the evolution of the microstructure at low strain variations under bending fatigue conditions, and can support the prediction of the fatigue life of 316LVM stainless steel oligocrystalline microdevices like coronary artery stents.}, language = {en} } @misc{FellahHezilBourasetal., author = {Fellah, Mamoun and Hezil, Naouel and Bouras, Dikra and Obrosov, Aleksei and Samad, Mohammed Abdul and Montagne, Alex and Abd-Elmonem, Assmaa and Din, Sayed M El and Weiß, Sabine}, title = {Structural, mechanical and tribological performance of a nano structured biomaterial Co-Cr-Mo alloy synthesized via mechanical alloying}, series = {Journal of Materials Research and Technology}, volume = {25}, journal = {Journal of Materials Research and Technology}, issn = {2214-0697}, doi = {10.1016/j.jmrt.2023.06.031}, pages = {2152 -- 2165}, abstract = {The influence of milling time on the tribological behavior of a Co-Cr-Mo alloy designed for biomedical applications, synthesized via mechanical alloying is investigated. Elemental Co, Cr and Mo powders are milled using different milling times (2, 6, 12 and 18 h) in a high-energy ball mill. The resulting powders were subjected to cold uniaxial and hot isostatic pressing respectively, followed by sintering to obtain cylindrical samples, which were evaluated for their structural, mechanical and the wear behavior. Results showed that the grain and crystallite sizes of the powders decreased with increasing milling time, reaching low values of <10 μm and 32 μm respectively, at higher milling times. Furthermore, the wear rates and the coefficients of friction were lower, at higher milling times due to high densities (96\%), and higher elasto-plastic resistance, as presented by the H/E and H3/E2 values of 0.026 and 0.0021 GPa, respectively. Increased milling time enables the refinement of grains and reduction in porosity in the Co-Cr-Mo alloy, which in turn increases the alloy's elasto-plastic resistance and enhances its wear resistance.}, language = {en} } @misc{CelikAtapekPolatetal., author = {{\c{C}}elik, G{\"u}l{\c{s}}ah Akta{\c{s}} and Atapek, Şaban Hakan and Polat, Şeyda and Obrosov, Aleksei and Weiß, Sabine}, title = {Nitriding Effect on the Tribological Performance of CrN-, AlTiN-, and CrN/AlTiN-Coated DIN 1.2367 Hot Work Tool Steel}, series = {Materials}, volume = {16}, journal = {Materials}, number = {7}, issn = {1996-1944}, doi = {10.3390/ma16072804}, abstract = {In this study, heat-treated and multisurface engineered DIN 1.2367 tool steel was subjected to room and elevated temperature wear tests, and the effect of nitriding on its tribological behavior was investigated. CrN, AlTiN, and CrN/AlTiN coatings with a total thickness of 2 µm were obtained by arc cathodic physical vapor deposition on conventional heat-treated and gas-nitrided steels. The white layer formed during nitriding was removed, and a diffusion layer (100 µm) was achieved in the cross section of the steel having a tempered martensitic matrix. The highest surface hardness was attained with an integral coating (CrN/AlTiN), and surface hardness increased even more after nitriding due to the formation of a multicomponent ceramic layer on top of the diffusion layer. The room temperature wear tests performed against an alumina counterpart revealed that (i) CrN/AlTiN-coated steel had the highest friction coefficient of 0.26, which further increased to 0.33 by nitriding due to the increase in shear strength, and that (ii) with increasing surface hardness, the specific wear rates (W) of the heat-treated and coated steels could be ranked as follows: WCrN/AlTiN < WAlTiN < WCrN. The wear rates decreased when nitriding was carried out prior to coating. In order to simulate the aluminum extrusion conditions, hot wear behavior of the surfaces against AA6080 alloy at 450 °C was investigated. The hot wear tests revealed that (i) high friction coefficients were reached due to the adhesive characteristic of aluminum to the surfaces, (ii) the nitrided and CrN/AlTiN-coated sample exhibited the lowest wear rate among all studied surfaces, and (iii) the film damage on the worn surfaces mostly occurred in the form of droplet delamination.}, language = {en} } @misc{SafariImranWeiss, author = {Safari, Athar and Imran, Muhammad and Weiss, Sabine}, title = {A Comparative Study on Modified Johnson-Cook and Arrhenius-Type Constitutive Models to Predict the Hot Deformation Behaviour of Molybdenum-Hafnium-Carbide Alloy}, series = {Journal of Materials Engineering and Performance}, volume = {30}, journal = {Journal of Materials Engineering and Performance}, number = {3}, issn = {1059-9495}, doi = {10.1007/s11665-021-05464-2}, pages = {1945 -- 1956}, abstract = {Molybdenum alloys are commonly used as tool material for high-temperature deformation processes like forming or forging. For these types of application, the material has to withstand static load at elevated temperatures. To investigate the high-temperature performance of the material, uniaxial hot tensile tests were performed on a Mo-1.2\% Hf-0.1\% C alloy (MHC) over the temperature range of 1173-1473 K with intervals of 100 K and strain rates of 0.001, 0.01 and 0.1 s-1 up to the fracture of the specimen. The flow stress decreases with increase in temperature and the reduction in strain rate. This behaviour could be related to the increasing rate of restoration mechanisms, i.e. dynamic recrystallization or recovery as well as to the decrease in the strain hardening rate. Microstructure of the two most critical hot deformation conditions were shown and compared. Based on modified Johnson-Cook and strain-compensated Arrhenius-type models, constitutive equations were established to predict the high-temperature flow stress of the respective MHC alloy. The accuracy of both models was evaluated by comparing the predicted stress values and the values obtained from experiments. Correlation coefficient, average absolute relative error, the number of material constants involved and the computational time required for evaluating the constants were calculated to quantify and compare the precision of both models. The flow stress values predicted by the constitutive equations are in good agreement with the experimental results. At lower strain rates (0.001 and 0.01 s-1), distinct deviation from the experimental results can be observed for the modified Johnson-Cook model. Despite the longer evaluation time and the larger number of material constants, the deformation behaviour, tracked by the Arrhenius-type model is more accurate throughout the entire deformation process.}, language = {en} } @misc{BourasFellahBarilleetal., author = {Bouras, Dikra and Fellah, Mamoun and Barille, Regis and Weiß, Sabine and Samad, Mohammed Abdul and Alburaikan, Alhanouf and Khalifa, Hamiden Abd El-Wahed and Obrosov, Aleksei}, title = {Improvement of photocatalytic performance and sensitive ultraviolet photodetectors using AC-ZnO/ZC-Ag2O/AZ-CuO multilayers nanocomposite prepared by spin coating method}, series = {Journal of Science: Advanced Materials and Devices}, volume = {9}, journal = {Journal of Science: Advanced Materials and Devices}, number = {1}, issn = {2468-2179}, doi = {10.1016/j.jsamd.2023.100642}, abstract = {Morphological and optical properties of a multilayer film (CAZO/CZAO/ZACO) prepared by spin-coating method and deposited on a glass substrate were evaluated. The study was initially carried out for each layer, individually and then as a multilayer subsequently. Structural properties using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), infrared spectra (IR) and X-ray photoelectron Spectroscopy (XPS) showed the presence of three phases of zinc, copper and silver oxides at different levels. The CZAO sample observed with scanning electron microscope (SEM) showed an excellent porous surface with a large deformation in the multilayer configuration. Doping with zinc and copper in the silver crystal lattice improved the crystal structure and reduced the optical energy gap, thus increasing the optical absorbance and refractive index. The dielectric constants and showed an increase in the optical polarization values for lower photonic energies. The maximum degradation rate for photocatalysts of methylene blue was 89 \% for a 5-h exposure period with CAZO/CZAO/ZACO while it reached 71 \% for the CZAO sample during the same time period. The sensitivity of samples to light proved that the presence of ultraviolet radiation increases the number of holes trapped by oxygen ions and causes more free electrons and contribute to a better production of photocurrent than in darkness.}, language = {en} } @misc{YangEisentrautWeissetal., author = {Yang, Yitong and Eisentraut, Mark and Weiß, Sabine and Bolz, Sebastian}, title = {Comparison of the data from two EBSD system to verify the accuracy of the technique}, series = {AK Treffen Mikrostrukturcharakterisierung im REM", Ruhr-Uni Bochum, 30. November - 1. Dezember 2023}, journal = {AK Treffen Mikrostrukturcharakterisierung im REM", Ruhr-Uni Bochum, 30. November - 1. Dezember 2023}, address = {Bochum}, pages = {11}, language = {en} } @misc{EmdadiYangBolzetal., author = {Emdadi, Aliakbar and Yang, Yitong and Bolz, Sebastian and Stryzhyboroda, Oleg and Tovar, Michael and Gein, Sergej and Hecht, Ulrike and Weiß, Sabine}, title = {Mechanisms of necklace recrystallization in a BCC Fe-Al-Ta alloy with strengthening Laves phase precipitates}, series = {Scripta Materialia}, volume = {237}, journal = {Scripta Materialia}, issn = {1359-6462}, doi = {10.1016/j.scriptamat.2023.115705}, pages = {6}, abstract = {A necklace structure composed of fine grains formed by dynamic recrystallization was uncommonly observed at the pre-existing grain boundaries during the hot compression of a BCC Fe-25Al-1.5Ta alloy containing C14 - (Fe, Al)2Ta Laves phase precipitates. Two possible mechanisms for necklace formation were proposed; particle-stimulated nucleation and grain boundary bulging, depending on whether the original grain boundaries are occupied by C14 particles, or they are free of them. Recrystallization was initiated preferentially around the clusters of large particles at the boundaries containing particles. In contrast, the bulging of the original grain boundaries by strain-induced boundary migration was observed as a preliminary stage for necklace formation at the particle-free boundaries. The necklace structure expanded into the deformed volume in such a way that low-angle subgrain boundaries decorating the necklace layers transformed into grains with increasing deformation strain.}, language = {en} } @misc{LaskoYangWeissetal., author = {Lasko, Galina and Yang, Yitong and Weiss, Sabine and Schmauder, Siegfried and Dogahe, Kiarash}, title = {FEM Simulations of Fatigue Crack Initiation in the Oligocrystalline Microstructure of Stents}, series = {Materials}, volume = {16}, journal = {Materials}, number = {17}, doi = {10.3390/ma16176003}, pages = {17}, abstract = {For over two decades, vascular stents have been widely used to treat clogged vessels,serving as a scaffold to enlarge the narrowed lumen and recover the arterial flow area. High-purityoligocrystalline austenitic steel is usually applied for the production of stents. Despite the popularityand benefit of stenting, it still may cause serious clinical adverse issues, such as in-stent restenosisand stent fracture. Therefore, the study of the mechanical properties of stents and in particularthe prediction of their life cycles are in the focus of materials research. In our contribution, withinthe finite element method, a two-scale model of crack initiation in the microstructure of stents iselaborated. The approach is developed on the basis of the physically based Tanaka-Mura model(TMM), considering the evolution of shear bands during the crack initiation phase. The model allowsfor the analysis of the microstructure with respect to the life cycles of real materials. The effects ofdifferent loading conditions, grain orientation, and thickness of the specimen on W{\"o}hler curves wereanalysed. It was found that the microstructural features of oligocrystals are very sensitive to differentloading conditions with respect to their fatigue behaviour and play a major role in fatigue crackinitiation. Different grain-orientation distributions result in qualitative and quantitative differencesin stress distribution and in the number of cycles for crack initiation. It was found that presence ofa neutral zone in the cut-out of the microstructure under three-point-bending loading conditionschanges the qualitative and quantitative patterns of stress distribution and affects the number ofcycles for crack initiation. It was found that under both tensile and bending loading conditions,thicker specimens require more cycles for crack initiation. The W{\"o}hler curves for crack initiation inoligocrystalline microstructures of stents could be compared with the ones in the experiment, takinginto account that for high cyclic fatigue (HCF), typically, more than 70\% of the cycles refer to crackinitiation. The developed numerical tools could be used for the material design of stents}, language = {en} } @misc{DahmaniFellahHeziletal., author = {Dahmani, Marwa and Fellah, Mamoun and Hezil, Naouel and Benoudia, Mohamed-Cherif and Obrosov, Aleksei and El-Hiti, Gamal A. and Weiß, Sabine}, title = {Bioactivity and tribological performance of a novel nano-biomaterial beta-type Ti-alloy}, series = {Journal of materials research and technology}, volume = {36}, journal = {Journal of materials research and technology}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2214-0697}, doi = {https://doi.org/10.1016/j.jmrt.2025.03.180}, pages = {2297 -- 2316}, abstract = {This study investigates the bioactivity; wear performance, and topography of a novel beta-type titanium-based alloy using techniques such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and 2D and 3D analysis. The tribological test was evaluated using a ball-on-disk tribometer in a wet environment. Different loads of 2, 6, and 10 N were applied during the evolution. The data results indicate a significant effect of the milling process on the formation of the hydroxyapatite layer on the surfaces of the Ti-Nb-Mo alloy. Both the wear volume and rate showed a consistent trend of decrease as the milling time increased from 2 to 12 h for all applied loads. The minimum values of wear and volume were reached after 12 h of milling. The improvement in tribological behavior can be attributed to the improved mechanical properties of the alloys. In addition, the significant presence of niobium (Nb) and molybdenum (Mo) plays a critical role in achieving high coefficient of friction values. The primary wear mechanism observed in the Ti-25Nb-25Mo system was adhesive wear in addition to abrasive wear. With its lower Young's modulus and favorable biological and tribological properties, the Ti-25Nb-25Mo alloy represents a promising option for bone tissue applications in orthopedics.}, language = {en} } @misc{EmdadiJenschSzyndleretal., author = {Emdadi, Aliakbar and Jensch, Felix and Szyndler, Joanna and Huang, Hsuan-Po and H{\"a}rtel, Sebastian and Weiß, Sabine}, title = {Void closure behavior during hot forming of an Fe-Al alloy}, series = {Materials research proceedings}, volume = {54}, journal = {Materials research proceedings}, publisher = {IWA Publishing}, address = {Millersville, PA}, isbn = {978-1-64490-359-9}, issn = {2474-395X}, doi = {10.21741/9781644903599-99}, pages = {927 -- 935}, abstract = {Hot forging is a forming process that can be used as a post-processing treatment to close residual porosity and refine the microstructure of additively manufactured materials, resulting in improved mechanical properties. During hot forging, void closure occurs through plastic deformation resulting from a predominantly compressive stress state at elevated temperatures. In the present work, Fe-25Al-1.5Ta (at. \%) samples have been produced by laser powder bed fusion (LPBF) using a larger layer thickness and scan speed than commonly used to achieve a target porosity fraction of approximately 10\%. Full densification is attempted in the subsequent hot compression step at various height reduction ratios. The as-built LPBF samples contained 8-10\% voids. After deformation to true strains of 0.2, 0.4, and 0.6, the void fraction decreased significantly to approximately 4\%, 2.3\%, and 1.1\%, respectively. Hot compression resulted in the complete closure of large pores with a size range of 200-300 µm and a significant reduction in the size of small to medium pores. These results show potential for improving the productivity of the LPBF by speeding up the process by increasing layer thickness and scanning speed while maintaining a reasonable density. Full densification should be achieved by subsequent hot forging.}, language = {en} } @misc{ErtugrulEmdadiJedynaketal., author = {Ertugrul, G{\"o}khan and Emdadi, Aliakbar and Jedynak, Angelika and Weiß, Sabine and H{\"a}rtel, Sebastian}, title = {Hot forming behavior of tungsten carbide reinforced Ni-based superalloy 625 additively manufactured by laser directed energy deposition}, series = {Additive manufacturing letters}, volume = {13}, journal = {Additive manufacturing letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2772-3690}, doi = {10.1016/j.addlet.2025.100267}, pages = {1 -- 12}, abstract = {The demands of high-performance industries such as aerospace, automotive, tool manufacturing, oil, and gas industries are driving the innovation in high-performance materials and their production methods. This study explores the impact of hybrid manufacturing, specifically the effect of the addition of tungsten carbide (WC/W2C) via Laser-Directed Energy Deposition (L-DED), on the hot workability, hardness, and microstructure of nickel-based superalloy Inconel 625 (IN625). IN625 is known for its high temperature and high corrosion resistance, and tungsten carbide for its high wear resistance and grain refinement effect. The integration of WC/W2C particles into the IN625 matrix, in addition to the use of the hybrid approach of additive manufacturing followed by a hot-forming process, significantly influences the microstructure and mechanical behavior of the material. Thus, while incorporation of the WC/W2C can strengthen the material and extend the mechanical limitations, its full impact, including any potential usages, should be thoroughly evaluated for the intended application of the materials. To understand the effect of WC/W2C, additive manufacturing of IN625 both with and without WC/W2C and isothermal hot compression was carried out. The objective is to analyze the differences in microstructure and properties between L-DED manufactured IN625, and WC-reinforced IN625, and their hot-forming behavior, focusing on the effects of WC addition and post-deformation on microstructure and mechanical properties. This work represents the first investigation into the effect of WC/W2C hard particles on the hot-forming process of additively manufactured Ni-based metal matrix composites.}, language = {en} } @misc{EmdadiBolzJenschetal., author = {Emdadi, Aliakbar and Bolz, Sebastian and Jensch, Felix and Tovar, Michael and Weiß, Sabine}, title = {On the hot deformation of a Fe-Al-Ta iron aluminide prepared via laser powder bed fusion}, series = {Crystals}, volume = {13}, journal = {Crystals}, number = {4}, publisher = {MDPI}, address = {Basel}, issn = {2073-4352}, doi = {10.3390/cryst13040627}, pages = {1 -- 12}, abstract = {In the present work, a combined process of laser powder bed fusion (LPBF) and hot working in terms of microstructure refinement was investigated for Fe-25Al-1.5Ta alloy samples. Uniaxial compression tests were carried out parallel and perpendicular to the building direction (BD) at 1000 °C, where BCC A2-phase was stable, at a strain rate of 0.0013 s-1. The true stress-true strain curves indicated a broad flow stress peak followed by a slight decrease, which is typical for dynamic recrystallization (DRX) of conventional BCC metals such as ferritic iron. A negligible dependence in the flow stress behavior on the compression direction was observed. DRX initiated at a stress of 18.7 MPa for the sample compressed parallel to the BD, corresponding to a true strain of 0.011, and at 18.1 MPa for the samples compressed normal to the BD, which corresponded to a true strain of 0.010. The microstructural investigations by electron backscatter diffraction (EBSD) showed that the relatively coarse and elongated grains of the as-LPBF builds were significantly refined after hot working. The microstructure of the compressed samples mainly consisted deformed grains. These were fragmented by sub-grains bounded by low-angle boundaries independent of the compression axis, indicating the occurrence of dynamic recovery (DRV) during hot working. In addition, a few equiaxed, small grains were observed in the pre-existing grain boundaries, which formed due to DRX. Most pores in the as-LPBF builds were closed after hot compression, particularly in the central region of the deformed specimens where the compressive stress state is dominant. In summary, hot compression reveals a practical thermomechanical post-processing treatment for Fe-Al-Ta iron aluminides built by LPBF. The hot working refines the epitaxially elongated microstructure of the as-LPBF builds by DRV/DRX and reduces the porosity.}, language = {en} } @misc{EmdadiYangSzyndleretal., author = {Emdadi, Aliakbar and Yang, Yitong and Szyndler, Joanna and Jensch, Felix and Ertugrul, G{\"o}khan and Tovar, Michael and H{\"a}rtel, Sebastian and Weiß, Sabine}, title = {Highly printable Fe₃Al intermetallic alloy}, series = {Metals : open access journal}, volume = {16}, journal = {Metals : open access journal}, number = {5}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/met16010005}, pages = {1 -- 15}, abstract = {Intermetallic Fe₃Al-based alloys reinforced with Laves-phase precipitates are emerging as potential replacements for conventional high-alloy steels and possibly polycrystalline Ni-based superalloys in structural applications up to 700 °C. Their impressive mechanical properties, however, are offset by limited fabricability and poor machinability due to their severe brittleness. High tool wear during finish-machining, which is still required for components such as turbine blades, remains a key barrier to their broader adoption. In contrast to conventional manufacturing routes, additive manufacturing offers a viable solution by enabling near-net-shape manufacturing of difficult-to-machine iron aluminides. In the present study, laser powder bed fusion was used to produce an Fe-25Al-1.5Ta intermetallic containing strengthening Laves-phase precipitates, and the porosity, microstructure and phase composition were characterized as a function of the process parameters. The results showed that preheating the build plate to 650 °C effectively suppressed delamination and macrocrack formation, even though noticeable cracking still occurred at the high scan speed of 1000 mm/s. X-ray tomography revealed that samples fabricated with a lower scan speed (500 mm/s) and a higher layer thickness (0.1 mm) contained larger, irregularly shaped pores, whereas specimens printed at the same volumetric energy density (40 J/mm3) but with different parameter sets exhibited smaller fractions of predominantly spherical pores. All samples contained mostly elongated grains that were either oriented close to <001> relative to the build direction or largely texture-free. X-ray diffraction confirmed the presence of Fe₃Al and C14-type (Fe, Al)₂Ta Laves phase in all samples. Hardness values fell within a narrow range (378-398 HV10), with only a slight reduction in the specimen exhibiting higher porosity.}, language = {en} } @misc{JenschSviridovDubininetal., author = {Jensch, Felix and Sviridov, Alexander and Dubinin, Sergej and Karabulut, Fatih and Weiß, Sabine and H{\"a}rtel, Sebastian}, title = {Parameter optimization for low-porosity Ti-6Al-4V parts produced using accelerated PBF-LB process}, series = {Progress in additive manufacturing}, journal = {Progress in additive manufacturing}, publisher = {Springer}, address = {Cham}, issn = {2363-9520}, doi = {10.1007/s40964-025-01510-w}, pages = {1 -- 17}, abstract = {In this study, the influence of various process parameters on the porosity of Ti-6Al-4V parts fabricated via Powder Bed Fusion - Laser Based (PBF-LB) is investigated. Three different layer thicknesses (30 μm, 60 μm, and 120 μm) were analyzed to define process windows enabling a build-rate acceleration while keeping the porosity below 0.1\%. Through iterative parameter refinement, the effects of laser power, scan speed and hatch distance were examined in terms of linear energy density (LED), energy transmission density (ETD) and volumetric energy density (VED), and their influence on the formation of process-related defects such as pores. Correlations between these energy metrics and pore formation types (keyhole vs. lack-of-fusion) are discussed. The results demonstrate that process acceleration by a factor of more than 3 is possible while maintaining high quality of the components in terms of internal porosity. In addition, an accelerated method for manufacturing components using the PBF-LB process is presented, in which components are manufactured at very high build-rates but with increased porosity and then brought to the target porosity of 0.1\% using the HIP process. This has made it possible to accelerate the build-rate in PBF-LB production by a further 32\%. Accounting for the additional time required for HIP, the HIP route is faster than using the accelerated, which achieves the target porosity in as-built condition, for parts larger than 1421 cm3.}, language = {en} }