Correlations between shadow glass transition, enthalpy recovery and medium range order in a Pd40Ni40P20 bulk metallic glass

Two distinct enthalpic states were induced in a bulk metallic glass through cyclic annealing at 473 K ( ) and 558 K ( ), targeting individual or relaxation modes, here referred to as the so-called shadow glass transition (SGT) and enthalpy recovery, respectively. Fluctuation electron microscopy (FEM) was employed to systematically investigate the medium-range order (MRO) within the amorphous structure in the post-annealed state and subsequent quenching after the SGT. Comparing the results with literature data from the same glass quenched from SCL samples, a significant increase in MRO was observed after annealing at . Conversely, samples quenched directly after the SGT exhibit a reduced MRO, similar to those quenched from the supercooled liquid (SCL). These findings suggest a correlation between the SGT and a decrease in MRO within the glass, a phenomenon discussed in the context of underlying structural rearrangements associated with relaxation, encompassing the SGT. Additionally, prolonged annealing at led to glass separation in the material, with remixing observed as an endothermic transformation in the SCL. The origin of this transformation is discussed as either a potential liquid–liquid or glass–liquid transition and their connection to modifications in medium-range order.

Manoel W. da Silva Pinto, Lydia Daum, Harald Rösner, Gerhard Wilde

Severe plastic deformation for producing superfunctional ultrafine-grained and heterostructured materials: An interdisciplinary reviewd

Ultrafine-grained and heterostructured materials are currently of high interest due to their superior mechanical and functional properties. Severe plastic deformation (SPD) is one of the most effective methods to produce such materials with unique microstructure-property relationships. In this review paper, after summarizing the recent progress in developing various SPD methods for processing bulk, surface and powder of materials, the main structural and microstructural features of SPD-processed materials are explained including lattice defects, grain boundaries and phase transformations. The properties and potential applications of SPD-processed materials are then reviewed in detail including tensile properties, creep, superplasticity, hydrogen embrittlement resistance, electrical conductivity, magnetic properties, optical properties, solar energy harvesting, photocatalysis, electrocatalysis, hydrolysis, hydrogen storage, hydrogen production, CO2 conversion, corrosion resistance and biocompatibility. It is shown that achieving such properties is not limited to pure metals and conventional metallic alloys, and a wide range of materials are currently processed by SPD, including high-entropy alloys, glasses, semiconductors, ceramics and polymers. It is particularly emphasized that SPD has moved from a simple metal processing tool to a powerful means for the discovery and synthesis of new superfunctional metallic and nonmetallic materials. The article ends by declaring that the borders of SPD have been extended from materials science and it has become an interdisciplinary tool to address scientific questions such as the mechanisms of geological and astronomical phenomena and the origin of life.

 M. Peterlechner, G. Wilde

Direct Recycling at the Material Level: Unravelling Challenges and Opportunities through a Case Study on Spent Ni-Rich Layered Oxide-Based Cathodes

Direct recycling is a key technology for enabling a circular economy of spent lithium ion batteries (LIBs). For cathode active materials (CAMs), it is regarded as the tightest closed-loop and most efficient approach among current recycling techniques as it simply proceeds via re-lithiation and reconstruction of aged CAMs instead of separating them into elemental components. In this work, spent, i.e., morphologically and structurally decomposed CAM based on LiNi0.83Co0.12Mn0.05O2 (NCM-831205) is restored by mimicking conditions of original CAM synthesis. After evaluating and optimizing the high-temperature duration for CAM restoration and subsequent washing procedure, the recycled CAM is shown to maintain poly-crystallinity and tap density, successfully recover specific surface area, lithium content, crystal structure in surface and bulk, while, however, only partly the original secondary particle size and shape. Though, comparable in initial 100 charge/discharge cycles with pristine CAM in lithium ion-cells, the subsequent increase in resistance and capacity fading remains a challenge. High temperature during recycling can be regarded as a key challenge on material level, as it not only promotes detrimental surface carbonate species from residual carbon black but also enhances cation disorder and micro-/nanoscopic porosity through oxygen release, likely in de-lithiated, thus less thermally stable regions of cycled NCM.

Maike Michelle Gnutzmann, Ardavan Makvandi, Bixian Ying, Julius Buchmann, Marco Joes Lüther, Bianca Helm, Peter Nagel, Martin Peterlechner, Gerhard Wilde, Aurora Gomez-Martin, Karin Kleiner, Martin Winter, Johannes Kasnatscheew

Non-volatile nanophotonic hybrid optical switch with integrated phase change material assisted with graphene-microheater

Neuromorphic computing based on integrated photonic circuits on-chip is a burgeoning area aiming to achieve high-speed, energy-efficient, and low-latency data processing to alleviate artificial intelligence-related applications, such as autonomous driving and speech recognition. Outstanding properties of phase change materials, such as reversible and fast switching of the states and high index contrast together with a wide spectral region integrated in nanophotonic devices provide a unique on-chip hybrid system to obtain fast modulators, switches and to realize neuromorphic systems on-chip. We designed on-chip reconfigurable broadband nanocrystalline graphene-assisted waveguide switch and memory unit covering the whole telecommunication C-band based on absorption modulation of integrated Ge2Sb2Te5 (GST) PCM cells. GST state switching is triggered via patterned nanocrystalline graphene external microheaters placed on top of silicon nitride waveguide and beneath PCM cell.

Anna P. Ovvyan, Niklas Vollmar, Zhongyu Tang, Seongmin Jo, Martin Salinga, Wolfram Pernice

Integrated Photonics Platforms III, 19 June 2024

Coupling of alloy chemistry, diffusion and structure by grain boundary engineering in Ni–Cr–Fe

The diffusion–microstructure correlations for grain boundaries (GBs) in the technologically-relevant Ni-based 602CA alloy are investigated. Prolonged annealing treatments up to 744 h create distinct GB complexions with specific segregation–precipitation–structure states. Globular M23C -type carbides at straight GBs and plate-like carbides together with NiAl-enriched ( -type) particles at hackly GBs are found to co-exist. Moreover, an atomic-scale GB spinodal-like decomposition, especially at straight GBs, is observed. The co-existence of the two distinct states of general high-angle GBs, indicated by tracer diffusion experiments and verified by a detailed structure examination, is explained via state-of-the-art measurements of local elastic strains. In a course of annealing at 873 K, the relatively “fast” diffusivities are found to increase by a factor of 10 or more as a result of a coupled evolution of the GB plate-like precipitates and the irregular GB structures, whereas the relatively ”slow” diffusivites remained practically unchanged representing the contributions of straight interfaces with spherical precipitates. Thus, the diffusion properties of high-angle GBs evolve together with characteristic changes of GB complexions distinguished by a growth of carbide- and -type precipitates and a concomitant generation of GB dislocation networks. The obtained results provide novel insights into grain boundary tailoring by utilizing structure – kinetics correlations involving segregation, precipitation and the evolution of interface defects.

Baixue Bian, Shabnam Taheriniya, G. Mohan Muralikrishna, Sandipan Sen, Christoph Gammer, Ingo Steinbach, Sergiy V. Divinski, Gerhard Wilde

Grain boundary self- and Mn impurity diffusion in equiatomic CoCrFeNi multi-principal element alloy

Grain boundary self-diffusion of Co, Cr and Fe and impurity diffusion of Mn are measured in a coarse-grained equiatomic CoCrFeNi multi-principal alloy. The tracer diffusivities are determined in a wide temperature range of 643 K to 1273 K, which encompasses both the C- and B-type kinetic regimes of grain boundary diffusion in polycrystalline materials after Harrison’s classification. At higher temperatures ( K), only one short-circuit (grain boundary) contribution is observed, while the existence of two distinct contributions is elucidated by thorough analysis of the penetration profiles corresponding to the C-type kinetic regime (643–703 K). The latter observations are explained in terms of a grain boundary phase decomposition after prolonged annealing below 700 K. The product of the segregation factor and the grain boundary width is found to be about 0.5 nm for all constituting elements. The grain boundary diffusion data indicate that Mn does not reveal a strong (if any) segregation in the equiatomic CoCrFeNi alloy.

Sandipan Sen, Marcel Glienke, Bhawna Yadav, Mayur Vaidya, K. Gururaj, K.G. Pradeep, Lydia Daum, Bengü Tas, Lukasz Rogal, Gerhard Wilde, Sergiy V. Divinski