@misc{FouziaFellahHeziletal., author = {Fouzia, Hammadi and Fellah, Mamoun and Hezil, Naouel and Aissani, Linda and Mimanne, Goussem and Mechachti, Said and Samad, Mohammed Abdul and Montagne, Alex and Iost, Alain and Weiß, Sabine and Obrosov, Aleksei}, title = {The effect of milling time on the microstructure and mechanical properties of Ti-6Al-4Fe alloys}, series = {Materials Today Communications}, volume = {27}, journal = {Materials Today Communications}, issn = {2352-4928}, doi = {10.1016/j.mtcomm.2021.102428}, pages = {11}, abstract = {Replacement of toxic and expensive vanadium (V) in medical grade titanium alloys with cheaper and non-toxic elements such as iron (Fe) or niobium (Nb), is an important step forward in developing safer and less expensive biomaterials. Evaluating the effect of different process parameters such as the milling time on the properties of these newly developed alloys helps in understanding and controlling their behavior. Hence, in this study, the influence of ball-milling duration (2, 6, 8, 12 and 18 h) on crystalline structure, phase evolution, densification, and mechanical characteristics of biomedical nanocrystalline Ti-6Al-4Fe (wt. \%) alloys is investigated. X-ray diffraction (XRD) confirmed that after 6 h of milling, aluminum (Al) and Fe completely dissolved into Ti matrix to form a solid solution of Ti (Al, Fe). XRD further revealed that the crystallite size decreased from 56 to 30 nm and the micro-strain increased with an increase in milling time. A decrease in porosity along with an increase in density is also observed for the alloys with increasing milling time. Moreover, the values of porosity obtained for the developed Ti-6Al-4Fe alloys ranged from 1 to 12 \%, which is comparable to the porosity of one of the cortical bones making it a potential candidate for bone replacements. Microhardness measurements showed that the hardness of the Ti-6Al-4Fe alloys was greater than the hardness of the conventional Ti-6Al-4V alloys. It was observed that the Ti-6Al-4Fe alloy fabricated with the powders milled for 2 h showed the lowest value of Young's Modulus. Milling time also had a significant effect on the surface roughness of the alloy samples, which showed a decreasing trend with increasing milling times.}, language = {en} } @misc{GrudininSidelevBleykheretal., author = {Grudinin, V. A. and Sidelev, D. V. and Bleykher, G. A. and Yuriev, Yu N. and Krivobokov, V. P. and Berlin, E. V. and Grigoriev, V. Yu and Obrosov, Aleksei and Weiß, Sabine}, title = {Hot target magnetron sputtering enhanced by RF-ICP source for CrNx coatings deposition}, series = {Vacuum}, volume = {191}, journal = {Vacuum}, issn = {0042-207X}, doi = {10.1016/j.vacuum.2021.110400}, pages = {9}, abstract = {This article describes hot Cr target magnetron sputtering enhanced by a radio-frequency inductively coupled plasma (RF-ICP) source in an Ar + N2 atmosphere. Optical emission spectroscopy revealed an opportunity to perform magnetron sputtering in an inert (Ar) atmosphere, while the CrNx coating can be deposited on a substrate in a chemically reactive atmosphere formed by the RF-ICP source. High stability and repeatability of deposition process were observed, and the deposition rate of the CrNx coatings increased from 106 to 127 nm/min as N2 flow rate rose. The power of the RF-ICP source and the N2 flow rate can be used to tailor and control deposition conditions. The XRD and WDS measurements showed the effect of deposition conditions on the crystal structure and elemental composition of CrNx coatings. It was found that the change of substrate bias, RF-ICP source power and N2 flow rate result in variation of coating stoichiometry from pure Cr to CrN.}, language = {en} } @misc{KrzywińskiSadowskiStefaniuketal., author = {Krzywiński, Kamil and Sadowski, Łukasz and Stefaniuk, Damian and Obrosov, Aleksei and Weiß, Sabine}, title = {Engineering and Manufacturing Technology of Green Epoxy Resin Coatings Modified with Recycled Fine Aggregates}, series = {International Journal of Precision Engineering and Manufacturing-Green Technology}, volume = {9}, journal = {International Journal of Precision Engineering and Manufacturing-Green Technology}, number = {1}, issn = {2198-0810}, doi = {10.1007/s40684-021-00377-w}, pages = {253 -- 271}, abstract = {Nowadays, the recycled fine aggregate sourced from construction and demolition waste is not frequently used in manufacturing of epoxy resin coatings. Therefore, the main novelty of the article is to prepare green epoxy resin coatings modified with recycled fine aggregate in a replacement ratio of natural fine aggregate ranged from 20 to 100\%. The microstructural properties of the aggregates and epoxy resin were analyzed using micro-computed tomography, scanning electron microscopy and nanoindentation. The macroscopic mechanical properties were examined using pull-off strength tests. The highest improvement of the mechanical properties was observed for epoxy resin coatings modified with 20\% of natural fine aggregate and 80\% of recycled fine aggregate. It has been found that even 100\% of natural fine aggregate can be successfully replaced using the recycled fine aggregate with consequent improvement of the pull-off strength of analyzed epoxy resin coatings. In order to confirm the assumptions resulting from the conducted research, an original analytical and numerical failure model proved the superior behavior of modified coating was developed.}, language = {en} } @misc{AissaniFellahChadlietal., author = {Aissani, Linda and Fellah, Mamoun and Chadli, Abdel Hakim and Samad, Mohammed Abdul and Cheriet, Abderrahmane and Salhi, Faiza and Nouveau, Corinne and Weiß, Sabine and Obrosov, Aleksei and Alhussein, Akram}, title = {Investigating the effect of nitrogen on the structural and tribo-mechanical behavior of vanadium nitride thin films deposited using R.F. magnetron sputtering}, series = {Journal of Materials Science}, volume = {56}, journal = {Journal of Materials Science}, number = {30}, issn = {1573-4803}, doi = {10.1007/s10853-021-06393-0}, pages = {17319 -- 17336}, abstract = {Magnetron sputtering is one of the most commonly used deposition techniques, which has received considerable attention in industrial applications. In particular, owing to its compatibility with conventional fabrication processes, it can produce and fabricate high-quality dense thin films of a wide range of materials. In the present study, nitrogen (N) was combined with pure vanadium in order to form binary nitride to improve its mechanical and tribological performance. To evaluate the influence of nitrogen on the structure of the as-deposited vanadium nitride (VN) coatings, the following techniques were used: XPS, XRD, SEM, AFM and optical profilometry. The residual stresses were determined by the curvature method using Stoney's formula. The hardness and Young's modulus were obtained by nanoindentation measurements. The friction behavior and wear characteristics of the films were evaluated by using a ball-on-disk tribometer. The obtained results showed that the N/V ratio increased with increasing the N2 flow rate while the deposition rate decreased. The preferred orientation was changed from (200) to (111) as the N2 flow rate increased with the presence of V-N and V-O binding energies as confirmed by XPS analysis. The nitrogen addition resulted in a columnar morphology and a fine structure with fine surface roughness. The VN thin film containing 49.5 at.\% of nitrogen showed the best performance: highest mechanical properties (hardness = 25 GPa), lowest friction coefficient (μ = 0.37) and lowest wear rate (Ws = 2.72 × 10-5 mm3N-1 m-1). A good correlation between the film microstructure, crystallite size, residual stress and mechanical and tribological properties was observed.}, language = {en} } @misc{ShapovalovShapovalovaOssenbrinketal., author = {Shapovalov, Oleg and Shapovalova, Mariia and Ossenbrink, Ralf and Heckel, Thomas and Michailov, Vesselin and Weiß, Sabine and Gaal, Mate}, title = {Verbessern der Korrosionsbest{\"a}ndigkeit eines hochtemperaturbest{\"a}ndigen Ultraschalld{\"a}mpfungsk{\"o}rpers mittels Laserstrahl-Auftragschweißen}, series = {DVS Berichte 2021}, journal = {DVS Berichte 2021}, publisher = {DVS Media GmbH}, address = {D{\"u}sseldorf}, isbn = {978-3-96144-147-1}, pages = {370 -- 377}, abstract = {W{\"a}hrend in einem konventionellen Ultraschallpr{\"u}fkopf ein Kunststoffd{\"a}mpfungsk{\"o}rper mit Kleber oder {\"O}l an einen Piezoschwinger angekoppelt ist, werden als Hochtemperaturl{\"o}sung feinpor{\"o}se sintermetallische D{\"a}mpfungsmaterialien mit einer Fl{\"u}ssigglasankopplung eingesetzt. Um dabei das Sintermetall vor dem korrosiven Angriff der Glasschmelze zu sch{\"u}tzten, wird am D{\"a}mpfungsk{\"o}rper gegenw{\"a}rtig Gold- oder Platinfolie zeit- und kostenaufwendig appliziert. In der aktuellen Arbeit wurde eine Methode zum Korrosionsschutz der sintermetallischen Oberfl{\"a}che aus rostfreiem Stahl mittels Laser-Pulverauftragschweißen entwickelt. Im Laufe einer Schweißparameterstudie auf dem Substratmaterial aus massivem rostfreiem Stahl wurde die Eignung unterschiedlicher Auftragsmaterialien auf Nickel- und Kobaltbasis untersucht. Dabei wurde zun{\"a}chst der Einfluss verschiedener Schweißparameter wie Laserleistung, Vorschubgeschwindigkeit und Pulvermenge auf die Auftragsqualit{\"a}t (Nahtform, Vermischungsgrad, Porosit{\"a}t) metallografisch bewertet. Anschließend wurden die aufgetragenen Schichten hinsichtlich ihrer Korrosionsbest{\"a}ndigkeit getestet. Der Kontakt mit einer fl{\"u}ssigen Glasmischung bei 500 °C hat bei keiner der beschichteten Proben sichtbare Korrosionswirkung gezeigt. Als Resultat der Schweißparameterstudie haben sich besonders die nickelbasierten Pulver als gut geeignete Materialien f{\"u}r den Prozess gezeigt. Die identifizierten Schweißparameter wurden im n{\"a}chsten Schritt erfolgreich an das sintermetallische Substrat angepasst.}, language = {de} } @misc{ErmilovaNikitinWeiss, author = {Ermilova, Evgeniia and Nikitin, Alexander and Weiß, Sabine}, title = {The Local Strain Evolution for Structured Sheet Metals During Uniaxial Deformation}, series = {Forming the Future : Proceedings of the 13th International Conference on the Technology of Plasticity}, journal = {Forming the Future : Proceedings of the 13th International Conference on the Technology of Plasticity}, editor = {Daehn, Glenn and Cao, Jian and Kinsey, Brad and Tekkaya, A. Erman and Vivek, Anupam and Yoshida, Yoshinori}, edition = {1}, publisher = {Springer, Cham}, isbn = {978-3-030-75381-8}, issn = {2367-1696}, doi = {10.1007/978-3-030-75381-8_143}, pages = {1701 -- 1711}, abstract = {Structured materials can be progressive alternatives to commonly used flat sheets because of their higher bending stiffness and stability compared to flat sheet metals, made of the same alloy. The application of sheet metals requires accurate information regarding their strength and deformation behavior. Such data are not commonly available and have to be measured by specific test setups and implementation of tests. The aim of this work is to obtain new knowledge about deformation mechanisms of structured sheet metals. Structured sheet metals (SSM) made of conventional deep-drawing steel DC04 were investigated by means of tensile tests. The influence of the structure type arrangement on the deformation behavior was analyzed. The evolution of local strains was analyzed by means of strain gauge measurements as well as 3D-displacement measurements with an ARAMIS highresolution camera system. Local orientation changes in different structural elements were measured using the electron backscatter diffraction technique.}, language = {en} } @misc{EmdadiBolzBuhletal., author = {Emdadi, Aliakbar and Bolz, Sebastian and Buhl, Johannes and Weiß, Sabine and Bambach, Markus}, title = {Laser Powder Bed Fusion Additive Manufacturing of Fe3Al-1.5Ta Iron Aluminide with Strengthening Laves Phase}, series = {Metals}, volume = {12}, journal = {Metals}, number = {6}, issn = {2075-4701}, doi = {10.3390/met12060997}, language = {en} } @misc{ShapovalovHeckelGaaletal., author = {Shapovalov, Oleg and Heckel, Thomas and Gaal, Mate and Weiß, Sabine}, title = {External Acoustical Damping on a Metallic Angle Wedge in a High Temperature Resistant Ultrasonic Probe}, series = {Acoustics Australia}, volume = {50}, journal = {Acoustics Australia}, number = {3}, issn = {1839-2571}, doi = {10.1007/s40857-022-00270-9}, pages = {343 -- 353}, abstract = {Ultrasonic probes for high-temperature applications are provided with metallic wedges, which can withstand the contact with the high temperature of the inspected structure. The ultrasonic signal travels within the wedge and gets reflected from its boundaries, causing interference signals called "ghost echoes". The current work presents an investigation of the additional damping effect provided by porous sintered metal plates applied onto the surface of the wedge. In particular, the study evaluates the effect of damping plate thickness on the interference signal level at different transmission frequencies. Damping plates made of sintered metal SIKA-R 15 AX were attached to a wedge prototype made of steel 1.4301. The study revealed, that the most effective thickness of damping plates in the selected frequency interval of 1 to 4 MHz is equal to 4 mm. The evaluation of the interference signal has shown that the application of such damping plates to the wedge surface contributes to an additional attenuation of an interference signal of 10 to 30 dB after 500 µs of signal propagation.}, language = {en} } @misc{MorozovaKehmObrosovetal., author = {Morozova, Iuliia and Kehm, Christian and Obrosov, Aleksei and Yang, Yitong and Miah, Kamal Uddin Mohammad and Uludintceva, Elena and Fritzsche, Sebastian and Weiß, Sabine and Michailov, Vesselin}, title = {On the Heat Treatment of Selective-Laser-Melted 316L}, series = {Journal of Materials Engineering and Performance}, volume = {32 (2023)}, journal = {Journal of Materials Engineering and Performance}, number = {10}, issn = {1544-1024}, doi = {10.1007/s11665-022-07404-0}, pages = {4295 -- 4305}, abstract = {The effect of heat treatment at various temperatures (650, 850, 1050, and 1100°C) and dwell times (10 min and 1 h) on the metallurgical and microstructural evolution as well as on the related tensile properties of stainless steel 316L processed by selective laser melting (SLM) has been systematically evaluated. The metallurgical and microstructural features such as defects, stability of the columnar-cellular structure and substructure, second phase particles, and phase transformation imparted by SLM and heat treatment have been discussed. It has been shown that the processing conditions specific to SLM significantly alter the kinetics of phase evolution compared to standard welding techniques which affects the accuracy of the prediction. The influence of these characteristics on tensile properties and hardness was elucidated. It was disclosed that with increasing heat treatment temperature there was a gradual increase in elongation but a decrease in strength related to the dislocation density and the development of the microstructure.}, language = {en} } @misc{MorozovaKrolickaObrosovetal., author = {Morozova, Iuliia and Kr{\´o}licka, Aleksandra and Obrosov, Aleksei and Yang, Yitong and Doynov, Nikolay and Weiß, Sabine and Michailov, Vesselin}, title = {Precipitation phenomena in impulse friction stir welded 2024 aluminium alloy}, series = {Materials Science and Engineering: A}, journal = {Materials Science and Engineering: A}, issn = {0921-5093}, doi = {10.1016/j.msea.2022.143617}, pages = {1 -- 11}, abstract = {Microhardness variations across the friction stir welded (FSW) and impulse friction stir welded (IFSW) AA2024-T351 joints have been elucidated by the transformations of the S-Al2CuMg phase with a special focus on a distinguished hardness peak within the heat-affected zone (HAZ) of the impulse welds. The increase in hardness within the stir zone (SZ) originated from the partial re-precipitation of the initial Guinier-Preston-Bagaryatsky zones (GPB) and metastable S needles, previously dissolved.) Formation and growth of stable S precipitates via coalescence accounted for the softening through the thermo-mechanically affected zone (TMAZ). The peak strengthening within the HAZ of the IFSW joints was mainly caused by the dense needle-shaped S particles, which can be explained by a mutual influence of the process specific temperature and strain cycles. Dislocations and subgrain boundaries introduced to the material due to plastic deformation facilitated the nucleation of strengthening S precipitates in the HAZ. It demonstrates that the impact of deformation should be considered by the characterization of the precipitation development in the HAZ.}, language = {en} } @misc{FigielBiedunkiewiczJachetal., author = {Figiel, Paweł and Biedunkiewicz, Anna and Jach, Katarzyna and Obrosov, Aleksei and Garbiec, Dariusz and Bik, Maciej and Sitarz, Maciej and Kucia, Zofia and Pawlyta, Mirosława and Weiß, Sabine}, title = {Ti-Mo-xTiC composites manufactured by U-FAST reactive sintering}, series = {International Journal of Refractory Metals and Hard Materials}, journal = {International Journal of Refractory Metals and Hard Materials}, number = {108}, issn = {0263-4368}, doi = {10.1016/j.ijrmhm.2022.105960}, pages = {1 -- 14}, abstract = {The paper presents the characteristics of Ti-Mo-xTiC composites manufactured under experimentally selected conditions using the upgraded field-assisted sintering technique (U-FAST). Mixtures of microstructural titanium powders and nc-Ti0.9Mo0.1C/C carbide powders protected from oxidation by a carbon shell were subjected to sintering. The powders with nc-Ti0.9Mo0.1C/C contents of 10 and 20 wt\% were used. The content of carbon forming the carbon shell was approximately 3 or 40 wt\%. Composites with near full density were reinforced with titanium carbides in a Ti-Mo matrix. The composites with the highest content of reinforcing phase are characterized by the highest values of hardness, Young's modulus and wear resistance. Although the hardness of these composites is similar to that of ceramics, their nature is not brittle. Despite the high value of the Young's modulus, the addition of hard particles of the reinforcing phase to the titanium matrix significantly increases the values of the H/E ratio of the composites compared to the reference samples of cp-Ti and Ti6Al4V. A comparison of the research results for the composites with the highest share of titanium carbides showed that lowering the sintering temperature from 1300 to 1150 °C resulted in the inhibition of grain growth, a reduction in composite heterogeneity, composite roughness and hardness as well as a rise in the Young's modulus. An increase in the sintering temperature from 1150 to 1300 °C contributed to the higher high angle grain boundaries (HAGB) content.}, language = {en} } @misc{PetkovBakalovaObrosovetal., author = {Petkov, Nikolay and Bakalova, Totka and Obrosov, Aleksei and Kashkarov, Egor B. and Kormunda, Martin and Kejzlar, Pavel and Bahchedzhiev, Hristo and Dadourek, Karel and Weiß, Sabine}, title = {Structural, mechanical, and tribological properties of CrCN coatings obtained by cathodic arc physical vapour deposition technology at different CH4/N2 gas ratio}, series = {Thin Solid Films}, volume = {766}, journal = {Thin Solid Films}, issn = {1879-2731}, doi = {10.1016/j.tsf.2022.139669}, abstract = {Chromium carbonitride coatings were deposited by cathodic arc physical vapor deposition technology at a temperature of 300 °C, as were used the reactive gasses CH4 and N2. The structural analysis of the CrN coating showed a polycrystalline structure with mixed CrN and Cr2N phases. All studied coatings, including the CrC exhibits fcc structure. The phases were confirmed by X-ray photoelectron spectroscopy measurements where a surface oxidation was also detected. The increase of the CH4 gas flow during the deposition process leads to a parabolic trend with the highest hardness of 33.5 GPa for the coating deposited at CH4 / N2 = 0.53. At the same time the lowest coefficient of friction for both counterparts Al2O3 and ZrO2 (0.28 and 0.26, respectively) were measured at CH4 / N2 = 1.86. The tribological tests reveal that the wear of the coatings increases with an increasing CH4 flow rate, whereas the coefficient of friction decreases. This observed contradiction is explained by a phenomenon described as the effect of Rebinder.}, language = {en} } @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} }