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2,064 results on '"Eckert, Jürgen"'

1. Stabilization of mechanical strength in a nanocrystalline CoCrNi concentrated alloy by nitrogen alloying

Author

Moravcik, Igor, Alfreider, Markus, Wurster, Stefan, Schretter, Lukas, Zadera, Antonin, Pernica, Vítezslav, Čamek, Libor, Eckert, Jürgen, and Hohenwarter, Anton

Subjects
Condensed Matter - Materials Science
Abstract

The mechanical performance and microstructures of a CoCrNi medium-entropy alloy (MEA) and NCoCrNi, alloyed with 0.5at% N, after high pressure torsion (HPT) and subsequent annealing treatments in a temperature range of 150-1000 {\deg}C were investigated. The introduction of N results in a reduction of grain size by 40% and ~10-15% increased hardness and bending strength after HPT. Both materials showed strain hardening and plasticity after HPT even at these strength levels over 1500 MPa which is induced by the saturated nanocrystalline state. Annealing at intermediate temperatures of 300-500 {\deg}C resulted in an additional increase of hardness and strength by ~20-40%, compared to the HPT deformed state. This effect was ~10 % more pronounced in the nitrogen alloyed CoCrNi that also showed better thermal stability. However, the increase in strength after 500 {\deg}C annealing was accompanied by a drastic loss of ductility in both materials., Comment: This work was supported by the project from the European Unions Horizon 2020 Research and Innovation Programme under the Marie Sk{\l}odowska-Curie Grant Agreement No101062549. In review as MSEA-D-24-02972

Published
2024

2. Nano-Patterned Pt-Based Metallic Glass Electrocatalysts with In-Situ Copper Oxide Foam for Enhanced Hydrogen Evolution

Author

Cai, Fei-Fan, Sarac, Baran, Akman, Adnan, Londoño, Juan J., Gümrükcü, Selin, Schweiger, Lukas, Hantusch, Martin, Schroers, Jan, Blatter, Andreas, Gebert, Annett, Spieckermann, Florian, and Eckert, Jürgen

Subjects
Condensed Matter - Materials Science, Physics - Chemical Physics
Abstract

Hydrogen is a promising energy carrier for replacing fossil fuels, and hydrogen production via hydrogen evolution reaction (HER) is an environmentally friendly option if electrocatalysts with low overpotentials and long-term stability are used. In this work, the electrocatalytic performance of $\mathrm{Pt_{57.5}Cu_{14.7}Ni_{5.3}P_{22.5}}$ bulk metallic glass (BMG) with flat, micro-patterned, and nano-patterned surfaces for HER in 0.5 M H2SO4 is studied. The nano-patterned Pt-BMG demonstrates outstanding long-term stability and self-improving behavior with a final overpotential of 150 mV and a Tafel slope of 42 $\mathrm{mV dec^{-1}}$ after 1000 linear sweep voltammetry (LSV) cycles, which is respectively 42% and 37% lower than in the first LSV cycle. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) indicate the formation of a layer of CuO/Cu2O foam deposited on top of the nano-patterned surface during the stability test of 1000 LSV cycles. A three-step process is proposed to explain the formation of CuxO foam via dynamic hydrogen bubble templating (DHBT) electrodeposition from Cu dissolution of the Pt-BMG without using copper salt. This work provides a method to create CuxO foams that could be used for various applications. Moreover, nano-patterned BMGs with DHBT deposition offer a feasible strategy to synthesize metal or metal-oxide foams., Comment: 28 pages, 9 figures (including supplementary information)

Published
2024

6. Hydrogen Evolution Reaction on Ultra-Smooth Sputtered Nanocrystalline Ni Thin Films in Alkaline Media-From Intrinsic Activity to the Effects of Surface Oxidation.

Author

Neumüller, Daniela, Rafailović, Lidija, Jovanović, Aleksandar, Skorodumova, Natalia, Pašti, Igor, Lassnig, Alice, Griesser, Thomas, Gammer, Christoph, and Eckert, Jürgen

Subjects
electrochemical surface oxidation, electrolysis, hydrogen evolution reaction, magnetron sputter deposition, water splitting
Abstract

Highly effective yet affordable non-noble metal catalysts are a key component for advances in hydrogen generation via electrolysis. The synthesis of catalytic heterostructures containing established Ni in combination with surface NiO, Ni(OH)2, and NiOOH domains gives rise to a synergistic effect between the surface components and is highly beneficial for water splitting and the hydrogen evolution reaction (HER). Herein, the intrinsic catalytic activity of pure Ni and the effect of partial electrochemical oxidation of ultra-smooth magnetron sputter-deposited Ni surfaces are analyzed by combining electrochemical measurements with transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. The experimental investigations are supplemented by Density Functional Theory and Kinetic Monte Carlo simulations. Kinetic parameters for the HER are evaluated while surface roughening is carefully monitored during different Ni film treatment and operation stages. Surface oxidation results in the dominant formation of Ni(OH)2, practically negligible surface roughening, and 3-5 times increased HER exchange current densities. Higher levels of surface roughening are observed during prolonged cycling to deep negative potentials, while surface oxidation slows down the HER activity losses compared to as-deposited films. Thus, surface oxidation increases the intrinsic HER activity of nickel and is also a viable strategy to improve catalyst durability.

Published
2023

7. Magnetron Sputtered Non-Toxic and Precious Element-Free Ti-Zr-Ge Metallic Glass Nanofilms with Enhanced Biocorrosion Resistance

Author

Sarac, Baran, Micusik, Matej, Putz, Barbara, Wurster, Stefan, Sharifikolouei, Elham, Xi, Lixia, Omastova, Maria, Spieckermann, Florian, Mitterer, Christian, and Eckert, Jürgen

Subjects
Condensed Matter - Materials Science
Abstract

The chemical composition and structural state of advanced alloys are the decisive factors in optimum biomedical performance. This contribution presents unique Ti-Zr-Ge metallic glass thin-film compositions fabricated by magnetron sputter deposition targeted for nanocoatings for biofouling prevention. The amorphous nanofilms with nanoscale roughness exhibit a large relaxation and supercooled liquid regions as revealed by flash differential scanning calorimetry. Ti\textsubscript{68}Zr\textsubscript{8}Ge\textsubscript{24} shows the lowest corrosion (0.17 \textmu A cm\textsuperscript{\textminus2}) and passivation (1.22 \textmu A cm\textsuperscript{\textminus2}) current densities, with the lowest corrosion potential of \textminus0.648 V and long-range stability against pitting, corroborating its excellent performance in phosphate buffer solution at 37 {\textdegree}C. The oxide layer is comprised of TiO\textsubscript{2}, TiO\textsubscript{\emph{x}} and ZrO\textsubscript{\emph{x}}, as determined using X-ray photoelectron spectroscopy by short-term ion-etching of the surface layer. The two orders of magnitude increase in the oxide and interface resistance (from 14 to 1257 {\textOmega} cm\textsuperscript{2}) along with an order of magnitude decrease in the capacitance parameter of the oxide interface (from 1.402 x 10\textsuperscript{\textminus5} to 1.677 x 10\textsuperscript{\textminus6} S s\textsuperscript{n} cm\textsuperscript{\textminus2}) of the same composition is linked to the formation of carbonyl groups and reduction of the native oxide layer during linear sweep voltammetry., Comment: 34 Pages, 5 Figures, 4 Tables, 13 Supplementary Figures

Published
2022
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8. Antibacterial activity, cytocompatibility, and thermomechanical stability of Ti40Zr10Cu36Pd14 bulk metallic glass.

Author

Rezvan, Amir, Sharifikolouei, Elham, Lassnig, Alice, Soprunyuk, Viktor, Gammer, Christoph, Spieckermann, Florian, Schranz, Wilfried, Najmi, Ziba, Cochis, Andrea, Scalia, Alessandro, Rimondini, Lia, Manfredi, Marcello, Eckert, Jürgen, and Sarac, Baran

Subjects
Antibacterial, Bulk metallic glass, Cytocompatible, Oral implant, Oral plaque
Abstract

This paper envisions Ti40Zr10Cu36Pd14 bulk metallic glass as an oral implant material and evaluates its antibacterial performance in the inhabitation of oral biofilm formation in comparison with the gold standard Ti-6Al-4V implant material. Metallic glasses are superior in terms of biocorrosion and have a reduced stress shielding effect compared with their crystalline counterparts. Dynamic mechanical and thermal expansion analyses on Ti40Zr10Cu36Pd14 show that these materials can be thermomechanically shaped into implants. Static water contact angle measurement on samples surface shows an increased surface wettability on the Ti-6Al-4V surface after 48 ​h incubation in the water while the contact angle remains constant for Ti40Zr10Cu36Pd14. Further, high-resolution transmission and scanning transmission electron microscopy analysis have revealed that Ti40Zr10Cu36Pd14 interior is fully amorphous, while a 15 ​nm surface oxide is formed on its surface and assigned as copper oxide. Unlike titanium oxide formed on Ti-6Al-4V, copper oxide is hydrophobic, and its formation reduces surface wettability. Further surface analysis by X-ray photoelectron spectroscopy confirmed the presence of copper oxide on the surface. Metallic glasses cytocompatibility was first demonstrated towards human gingival fibroblasts, and then the antibacterial properties were verified towards the oral pathogen Aggregatibacter actinomycetemcomitans responsible for oral biofilm formation. After 24 ​h of direct infection, metallic glasses reported a >70% reduction of bacteria viability and the number of viable colonies was reduced by ∼8 times, as shown by the colony-forming unit count. Field emission scanning electron microscopy and fluorescent images confirmed the lower surface colonization of metallic glasses in comparison with controls. Finally, oral biofilm obtained from healthy volunteers was cultivated onto specimens surface, and proteomics was applied to study the surface property impact on species composition within the oral plaque.

Published
2022

32. Structure-dynamics relationships in cryogenically deformed bulk metallic glass

Author

Spieckermann, Florian, Şopu, Daniel, Soprunyuk, Viktor, Kerber, Michael B., Bednarčík, Jozef, Schökel, Alexander, Rezvan, Amir, Ketov, Sergey, Sarac, Baran, Schafler, Erhard, and Eckert, Jürgen

Subjects
Condensed Matter - Materials Science
Abstract

The atomistic mechanisms occurring during the processes of aging and rejuvenation in glassy materials involve very small structural rearrangements that are extremely difficult to capture experimentally. Here we use in-situ X-ray diffraction to investigate the structural rearrangements during annealing from 77 K up to the crystallization temperature in Cu44Zr44Al8Hf2Co2 bulk metallic glass rejuvenated by high pressure torsion performed at cryogenic temperatures and at room temperature. Using a measure of the configurational entropy calculated from the X-ray pair correlation function, the structural footprint of the deformation-induced rejuvenation in bulk metallic glass is revealed. With synchrotron radiation, temperature and time resolutions comparable to calorimetric experiments are possible. This opens hitherto unavailable experimental possibilities allowing to unambiguously correlate changes in atomic configuration and structure to calorimetrically observed signals and can attribute those to changes of the dynamic and vibrational relaxations ({\alpha}-, {\beta}- and {\gamma}-transition) in glassy materials. The results suggest that the structural footprint of the {\beta}-transition is related to entropic relaxation with characteristics of a first-order transition. Dynamic mechanical analysis data shows that in the range of the {\beta}-transition, non-reversible structural rearrangements are preferentially activated. The low-temperature {\gamma}-transition is mostly triggering reversible deformations and shows a change of slope in the entropic footprint suggesting second-order characteristics.

Published
2021
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33. Direct observation of nanocrystal-induced enhancement of tensile ductility in a metallic glass composite

Author

Gammer, Christoph, Rentenberger, Christian, Beitelschmidt, Denise, Minor, Andrew M, and Eckert, Jürgen

Subjects
Engineering, Materials Engineering, Metallic glass, Nanocrystals, Transmission electron microscopy, In situ deformation, Manufacturing Engineering, Mechanical Engineering, Materials, Materials engineering, Mechanical engineering
Abstract

Bulk metallic glasses (BMGs) have attracted wide interest, but their successful application is hindered by their low ductility at room temperature. Therefore, the use of composites of a BMG matrix with crystalline secondary phases has been proposed to overcome this drawback. In the present work we demonstrate the fabrication of a tailored BMG nanocomposite containing a high density of monodisperse nanocrystals with a size of around 20 nm using a combination of mechanical and thermal treatment of Cu36Zr48Al8Ag8 well below the crystallization temperature. Direct observations of the interaction of the nanocrystals with a shear band during in situ deformation in a transmission electron microscope demonstrate that the achieved nanocomposite has the potential to inhibit catastrophic fracture in tension. This demonstrates that a sufficient number of nanoscale structural heterogeneities can be a route towards BMG composites with superior mechanical properties.

Published
2021

50. Effect of casting temperature on the solidification process and (micro)structure of Zr-based metallic glasses

Author

Zhishuai Jin, Fuyang Cao, Guanyu Cao, Chaojun Zhang, Ziao Qiu, Lunyong Zhang, Hongxian Shen, Sida Jiang, Yongjiang Huang, Mingzhen Ma, Eckert Jürgen, and Jianfei Sun

Subjects
Bulk metallic glasses (BMGs), Gravity casting, Solidification process, The distance–time curves, Solidification coefficient, Mining engineering. Metallurgy, TN1-997
Abstract

Bulk metallic glasses (BMGs) bear versatile advantages compared to traditional crystalline metallic materials. However, preparation of large size BMG components remains a great challenge due to the lack of understanding the casting dynamics of BMGs. The present work investigates the dynamics of the solidification process during casting of a Zr41.2Ti13.8Cu12.5Ni10Be22.5 BMG by measuring the time-dependent temperature evolution and constructing distance–time curves showing the progress of solidification. The experimentally probed temperature evolution proves that a higher casting temperature causes a lower cooling rate and induces more pronounced nanocrystal phase formation in the final BMG casting. Thus, optimization of the casting temperature is crucial for casting BMG components. The solidification coefficient K of the studied Zr-based BMG in copper mold was determined. The solidification time can be calculated with model: τ=M2K2. The solidification of the Zr-based BMG occurs in a narrow transition layer region following a “layer-by-layer” solidification mode. This feature is vital for designing the casting process appropriately to avoid the formation of casting defects in BMG components. The present work sheds new light on the solidification mechanism of bulk glass-forming liquids and underlines the importance of optimizing the technology and processing conditions for fabrication of BMG components with practical applications.

Published
2023
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