Neuste Publikationen aus unserem Institut

Journal of Applied Physics (2022) 132, 105107
© IMP&Jour. of App. Physics

Evidence for strain and a structural reset in Pd40Ni40P20 bulk metallic glass

The amorphous structure of a Pd-based metallic bulk glass after controlled heating into/cooling from the super-cooled liquid was investigated by fluctuation electron microscopy.

The results indicate that former activated α and/or β relaxation processes are deleted and thus a a defined structural reset was achieved.

The study suggests controlled heating into/cooling from the SCL as a possible standard protocol for investigations of metallic glass as it would afford a better reproducibility of experiments, independent of the fabrication, and/or thermal history of the samples.

Mark Stringe, Harald Rösner, Gerhard Wilde

Metals (2022) 12, 111

In Situ Generated Shear Bands in Metallic Glass Investigated by Atomic Force and Analytical Transmission Electron Microscopy

In this study, we investigated in situ generated shear bands in a metallic glass formed under tension in the transmission electron microscope and show, by accompanying thickness and surface measurements,
that their contrasts are related to thickness reduction, unlike ex situ samples where no change in thickness was observed.

Harald Rösner, Christian Kübel, Stefan Ostendorp and Gerhard Wilde

Effects of solutes on thermal stability, microstructure and mechanical properties in CrMnFeCoNi based alloys after high pressure torsion

The equiatomic Cantor alloy and Ni-enriched derivates of it ((CrMnFeCo)(x)Ni1-x with x = 0.8, 0.4, 0.08 and 0) were deformed by high pressure torsion to the saturation regime and subsequently annealed in a wide temperature range. The microstructural stability of the alloys was investigated in terms of grain growth and decomposition tendencies with an emphasis on Ni92 and Ni60 that are marking a transition from dilute solid solutions to HEA alloys. Ni92 and Ni100 show a larger grain size after HPT than the HEA type alloys Ni20 and Ni60, yet, they do exhibit a lower resistance to grain growth. Both HEA type alloys exhibit decomposition tendencies in the form of secondary phases (Ni20) or nanosized Cr-rich precipitates and Mn segregations to grain boundaries (Ni60), that reduce the grain boundary mobility. A comparison of the activation energies for grain growth and diffusion coefficients of the alloys shows a good qualitative agreement. The differences in microstructural stability are also reflected by the mechanical properties. All alloys show a small amount of hardening after annealing, followed by a softening for higher temperatures in case of dilute solid solutions. In contrast, the hardness of the HEA type alloys remains constant up to 450 degrees C (Ni60) or even increases up to 500 degrees C (Ni20) followed by a softening at higher annealing temperatures. The second phase formation with limited volume fractions has no effect on the modulus.

(C) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Tom Keil, Shabnam Taheriniya, Enrico Bruder, Gerhard Wilde, Karsten Durst

Decoupled alpha and beta relaxation kinetics in a thermally cycled bulk Pd40Ni40P20 glass

Reproducible thermodynamic sample states of a Pd40Ni40P20 bulk metallic glass are realized via differential scanning calorimetry by repeated quenching from the supercooled liquid state to temperatures well below the glass transition. Annealing treatments at 0.81 Tg and 0.96 Tg are embedded in the calorimetric method, changing the energetical state of the system. Varying the annealing times, a detailed and reproducible picture of the reversible relaxation dynamics with separated alpha- and beta-relaxation is obtained. An endothermic signature before Tg can either be provoked or depressed depending on the annealing temperature. The activation energy related to this process is obtained via Kissinger analyses yielding about 30 RTg. A large number of annealing cycles at 0.96 Tg irreversibly alters the response of the alpha-relaxation, while the mechanism of beta-relaxation is interestingly not influenced by this alternation. In order to extend the calorimetric response of the relaxation spectra to spatial resolution, the sample states were additionally analyzed using electron correlation microscopy providing information on the glass dynamics on an atomistic scale. The thus obtained kinetic parameters of local dynamics do not show an alteration of room temperature dynamics for different levels of alpha-relaxation, which is consistent with the results obtained via kinetic analyses of calorimetric data.

Mark Stringe, Katharina Spangenberg, Manoel Wilker da Silva Pinto, Martin Peterlechner, Gerhard Wilde

Journal of Energy Storage, Volume 44, Part B, 15 December 2021, 103479

Al2O3 protective coating on silicon thin film electrodes and its effect on the aging mechanisms of lithium metal and lithium ion cells

In this work, an investigation of the effect of Al2O3-coating on the aging mechanisms of silicon anode thin films in lithium metal and lithium ion cells is presented. Aging mechanisms, namely: loss of lithium inventory, loss of silicon active material and loss of utilizable capacity due to an increase of cell resistance were determined for both, Li||Si and Si||LiFePO4 cells. Al2O3-coating was shown to be an effective strategy to reduce the loss of lithium inventory, while having a marginal effect on decreasing the loss of silicon active material. Indeed, in case of Si||LiFePO4 cells, where fading is governed by loss of lithium inventory, a 5 nm Al2O3-coating leads to a significant reduction (-64%) of the capacity fade per cycle. On the contrary, in case of Li||Si, where the aging mechanism is governed by the loss of active material, Al2O3-coated and uncoated silicon showed comparable tendencies regarding the capacity fade per cycle. It emerges, also, that loss of silicon active material and loss of lithium inventory are independent of each other. This indicates that the main contribution of loss of lithium inventory is not the lithium trapped in electrically insulated silicon, but rather lithium consumed in the ongoing SEI formation. Al2O3-coating could reduce the latter due the insulating nature of the coating. Ex situ investigations of the SEI by means of X-ray photoelectron spectroscopy confirmed a decrease in solvent decomposition in presence of the Al2O3-coating.

Simone Casino, Bastian Heidrich, Ardavan Makvandi, Thomas Beuse, Tobias Gallasch, Martin Peterlechner, Gerhard Wilde, Martin Winter, Philip Niehoff

Journal of Alloys and Compounds, Volume 886, 15 December 2021, 161285

Synergizing mechanical properties and damping capacities in a lightweight Al-Zn-Li-Mg-Cu alloy

Alloys with synergized strength and damping capacity are in urgent need to eliminate vibrations and noises. Herein, a lightweight Al-Zn-Li-Mg-Cu alloy which exhibits similar strengths as traditional high-strength Al alloys and considerable damping capacities is developed. The resulting microstructures and precipitation behaviors are systematically characterized in the hot-rolled and cold-rolled alloy. Meanwhile, damping properties at low temperatures and high temperatures are thoroughly studied. Two rolled alloys show the same multi-segment characteristics, in which the effects of the strain amplitude and high temperature on tanφ are attributed to dislocation pinning and grain boundary viscoelastic sliding, respectively. The damping properties and low density, together with superb mechanical properties, demonstrate their practical application where noise and vibrations must be reduced.

Ruixuan Li, Gerhard Wilde, Yong Zhang

Juli 2021
Advanced Functional Materials 31, Nr. 38, 2021

Direct View on Non‐Equilibrium Heterogeneous Dynamics in Glassy Nanorods

Die Dynamik von Nanodrähten aus metallischem Glas wird im Transmissionselektronenmikroskop untersucht. Mit der Methode der Elektronenkorrelationsmikroskopie werden die Zeitskalen der heterogenen Glasdynamik in FeNiP lokal aufgelöst, was eine Entkopplung in zwei verschiedene Prozesse bei Raumtemperatur offenbart.

Katharina Spangenberg, Sven Hilke, Gerhard Wilde und Martin Peterlechner

Sept 2021
Shock and Vibration, vol. 2021, special issue Structural and Wave Propagation Effects in High-Energy Particle Impacts

Dynamic Radiation Effects Induced by Short-Pulsed GeV U-Ion Beams in Graphite and h-BN Targets

Targets of isotropic graphite and hexagonal boron nitride were exposed to short pulses of uranium ions with ∼1 GeV kinetic energy. The deposited power density of ∼3 MW/cm³ generates thermal stress in the samples leading to pressure waves. The velocity of the respective motion of the target surface was measured by laser Doppler vibrometry. The bending modes are identified as the dominant components in the velocity signal recorded as a function of time. With accumulated radiation damage, the bending mode frequency shifts towards higher values. Based on this shift, Young’s modulus of irradiated isotropic graphite is determined by comparison with ANSYS simulations. The increase of Young’s modulus up to 3 times the pristine value for the highest accumulated fluence of 3 × 1013 ions/cm2 is attributed to the beam-induced microstructural evolution into a disordered structure similar to glassy carbon. Young’s modulus values deduced from microindentation measurements are similar, confirming the validity of the method. Beam-induced stress waves remain in the elastic regime, and no large-scale damage can be observed in graphite. Hexagonal boron nitride shows lower radiation resistance. Circular cracks are generated already at low fluences, risking material failure when applied in high-dose environment.

Philipp Bolz, Philipp Drechsel, Alexey Prosvetov, Pascal Simon, Christina Trautmann and Marilena Tomut