TY - GEN A1 - Alontseva, Darya A1 - Safarova (Yantsen), Yuliya A1 - Voinarovych, Sergii A1 - Obrosov, Aleksei A1 - Yamanoglu, Ridvan A1 - Khoshnaw, Fuad A1 - Nessipbekova, Assem A1 - Syzdykova, Aizhan A1 - Yavuz, Hasan Ismail A1 - Kaliuzhnyi, Sergii A1 - Krasavin, Alexander A1 - Azamatov, Bagdat A1 - Khozhanov, Alexandr A1 - Olzhayev, Farkhad A1 - Weiß, Sabine T1 - Microplasma-Sprayed Titanium and Hydroxyapatite Coatings on Ti6Al4V Alloy: in vitro Biocompatibility and Corrosion Resistance: Part I T2 - Johnson Matthey Technology Review N2 - 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. KW - Endoprosthesis implants KW - Biocompatible coatings KW - Porosity KW - Surface roughness KW - In vitro test KW - Elastic modulus Y1 - 2025 UR - https://technology.matthey.com/content/journals/10.1595/205651325X17201903387613 U6 - https://doi.org/10.1595/205651325X17201903387613 VL - 69 IS - 1 SP - 45 EP - 58 ER - TY - GEN A1 - Alontseva, Darya A1 - Safarova (Yantsen), Yuliya A1 - Voinarovych, Sergii A1 - Obrosov, Aleksei A1 - Yamanoglu, Ridvan A1 - Khoshnaw, Fuad A1 - Nessipbekova, Assem A1 - Syzdykova, Aizhan A1 - Yavuz, Hasan Ismail A1 - Kaliuzhnyi, Sergii A1 - Krasavin, Alexander A1 - Azamatov, Bagdat A1 - Khozhanov, Alexandr A1 - Olzhayev, Farkhad A1 - Weiß, Sabine T1 - 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 T2 - Johnson Matthey Technology Review N2 - 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. KW - Endoprosthesis implants KW - Biocompatible coatings KW - Porosity KW - Surface roughness KW - In vitro test KW - Elastic modulus Y1 - 2025 U6 - https://doi.org/10.1595/205651325X17290035905758 SN - 2056-5135 VL - 69 (2025) IS - 1 SP - 59 EP - 75 ER - TY - GEN A1 - Synodinos, Alexis D. A1 - Karnatak, Rajat A1 - Aguilar‐Trigueros, Carlos A. A1 - Gras, Pierre A1 - Heger, Tina A1 - Ionescu, Danny A1 - Maaß, Stefanie A1 - Musseau, Camille L. A1 - Onandia, Gabriela A1 - Planillo, Aimara A1 - Weiss, Lina A1 - Wollrab, Sabine A1 - Ryo, Masahiro T1 - The rate of environmental change as an important driver across scales in ecology T2 - Oikos N2 - 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. KW - climate change KW - ecological communities KW - eco-evo feedbacks KW - transitions KW - global change KW - R-tipping KW - temporal ecology Y1 - 2023 U6 - https://doi.org/10.1111/oik.09616 SN - 0030-1299 VL - 2023 IS - 4 PB - Wiley ER - TY - GEN A1 - Yang, Yitong A1 - Weiß, Sabine T1 - In-situ investigation on cyclic bending deformation of oligocrystalline 316LVM steel for coronary stent application with EBSD T2 - International Conference on Strength of Materials 2022 N2 - 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. KW - Oligo-crystalline microstructure, in-situ bending fatigue test, EBSD, 316LVM austenitic steel, coronary stent, Y1 - 2022 UR - https://hal.science/hal-03829658v1 PB - HAL open science ER - TY - GEN A1 - Fellah, Mamoun A1 - Hezil, Naouel A1 - Bouras, Dikra A1 - Obrosov, Aleksei A1 - Samad, Mohammed Abdul A1 - Montagne, Alex A1 - Abd-Elmonem, Assmaa A1 - Din, Sayed M El A1 - Weiß, Sabine T1 - Structural, mechanical and tribological performance of a nano structured biomaterial Co–Cr–Mo alloy synthesized via mechanical alloying T2 - Journal of Materials Research and Technology N2 - 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. KW - Tribology KW - Wear resistance KW - Friction KW - Powder metallurgy KW - Co–Cr–Mo alloy Y1 - 2023 UR - https://www.sciencedirect.com/science/article/pii/S2238785423012796 U6 - https://doi.org/10.1016/j.jmrt.2023.06.031 SN - 2214-0697 VL - 25 SP - 2152 EP - 2165 ER - TY - GEN A1 - Çelik, Gülşah Aktaş A1 - Atapek, Şaban Hakan A1 - Polat, Şeyda A1 - Obrosov, Aleksei A1 - Weiß, Sabine T1 - Nitriding Effect on the Tribological Performance of CrN-, AlTiN-, and CrN/AlTiN-Coated DIN 1.2367 Hot Work Tool Steel T2 - Materials N2 - 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. KW - DIN 1.2367 KW - PVD coating KW - Wear KW - characterization Y1 - 2023 UR - https://www.mdpi.com/1996-1944/16/7/2804 U6 - https://doi.org/10.3390/ma16072804 SN - 1996-1944 VL - 16 IS - 7 ER - TY - GEN A1 - Safari, Athar A1 - Imran, Muhammad A1 - Weiss, Sabine T1 - A Comparative Study on Modified Johnson–Cook and Arrhenius-Type Constitutive Models to Predict the Hot Deformation Behaviour of Molybdenum-Hafnium-Carbide Alloy T2 - Journal of Materials Engineering and Performance N2 - 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. KW - constitutive equation KW - flow stress KW - hot tensile deformation KW - molybdenum-hafnium-carbide alloy (MHC) Y1 - 2021 U6 - https://doi.org/10.1007/s11665-021-05464-2 SN - 1059-9495 SN - 1544-1024 VL - 30 IS - 3 SP - 1945 EP - 1956 ER - TY - GEN A1 - Bouras, Dikra A1 - Fellah, Mamoun A1 - Barille, Regis A1 - Weiß, Sabine A1 - Samad, Mohammed Abdul A1 - Alburaikan, Alhanouf A1 - Khalifa, Hamiden Abd El-Wahed A1 - Obrosov, Aleksei T1 - Improvement of photocatalytic performance and sensitive ultraviolet photodetectors using AC-ZnO/ZC-Ag2O/AZ-CuO multilayers nanocomposite prepared by spin coating method T2 - Journal of Science: Advanced Materials and Devices N2 - 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. KW - Multilayer CAZO/CZAO/ZACO KW - Spin-coating KW - Energy gap KW - Photocatalysis KW - Photodetector KW - Nanostructures KW - Nanocomposites Y1 - 2024 U6 - https://doi.org/10.1016/j.jsamd.2023.100642 SN - 2468-2179 VL - 9 IS - 1 ER - TY - GEN A1 - Yang, Yitong A1 - Eisentraut, Mark A1 - Weiß, Sabine A1 - Bolz, Sebastian T1 - Comparison of the data from two EBSD system to verify the accuracy of the technique T2 - AK Treffen Mikrostrukturcharakterisierung im REM”, Ruhr-Uni Bochum, 30. November – 1. Dezember 2023 Y1 - 2023 UR - https://www.researchgate.net/publication/377636122_Comparison_of_the_data_from_two_EBSD_system_to_verify_the_accuracy_of_the_technique_AK-Treffen_Mikrostrukturcharakterisierung_im_REM_Ruhr-Uni_Bochum CY - Bochum ER - TY - GEN A1 - Emdadi, Aliakbar A1 - Yang, Yitong A1 - Bolz, Sebastian A1 - Stryzhyboroda, Oleg A1 - Tovar, Michael A1 - Gein, Sergej A1 - Hecht, Ulrike A1 - Weiß, Sabine T1 - Mechanisms of necklace recrystallization in a BCC Fe-Al-Ta alloy with strengthening Laves phase precipitates T2 - Scripta Materialia N2 - 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. Y1 - 2023 UR - https://www.sciencedirect.com/science/article/pii/S1359646223004281 U6 - https://doi.org/10.1016/j.scriptamat.2023.115705 SN - 1359-6462 SN - 1872-8456 VL - 237 ER - TY - GEN A1 - Lasko, Galina A1 - Yang, Yitong A1 - Weiss, Sabine A1 - Schmauder, Siegfried A1 - Dogahe, Kiarash T1 - FEM Simulations of Fatigue Crack Initiation in the Oligocrystalline Microstructure of Stents T2 - Materials N2 - 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 Wöhler 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 Wöhler 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 KW - SCHM 746/222-1 KW - WE 2671/11-1 Y1 - 2023 UR - https://www.mdpi.com/1996-1944/16/17/6003 U6 - https://doi.org/10.3390/ma16176003 VL - 16 IS - 17 ER - TY - GEN A1 - Dahmani, Marwa A1 - Fellah, Mamoun A1 - Hezil, Naouel A1 - Benoudia, Mohamed-Cherif A1 - Obrosov, Aleksei A1 - El-Hiti, Gamal A. A1 - Weiß, Sabine T1 - Bioactivity and tribological performance of a novel nano-biomaterial beta-type Ti-alloy T2 - Journal of materials research and technology N2 - 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. KW - Ti–25Nb–25Mo KW - Milling time KW - Bioactivity KW - Hydroxyapatite KW - Friction coefficient KW - Wear rate KW - Biomaterials Y1 - 2025 UR - https://www.sciencedirect.com/science/article/pii/S2238785425006908 U6 - https://doi.org/https://doi.org/10.1016/j.jmrt.2025.03.180 SN - 2214-0697 VL - 36 SP - 2297 EP - 2316 PB - Elsevier CY - Amsterdam ER -