Wei-Hua Wang

Although cryogenic thermal cycling effectively rejuvenates bulk metallic glasses, the atomistic mechanism governing their subsequent non-monotonic structural relaxation remains unresolved. In this work, molecular dynamics simulations were employed to investigate the mechanisms of cryogenic rejuvenation and post-rejuvenation relaxation in Zr46Cu46Al8 bulk metallic glass. Glassy samples prepared at different cooling rates were subjected to 30 cryogenic thermal cycles between 77 and 327 K, followed by long-term isothermal relaxation. The evolution of enthalpy, volume, density, radial distribution functions (RDFs), and Voronoi polyhedra was systematically analyzed to establish the relationship between energetic evolution and atomic-scale structural changes.,Cryogenic thermal cycling progressively rejuvenated the metallic glass, increasing the enthalpy per atom from -5.05 to -4.77 eV atom⁻¹, accompanied by a 2.15% increase in volume and only a 0.71% decrease in density after 30 thermal cycles. Despite these thermodynamic changes, RDF and Voronoi analyses revealed that the overall amorphous framework and dominant short-range order remained essentially unchanged, indicating that rejuvenation is governed primarily by localized atomic rearrangements rather than large-scale structural transformations. Unlike the monotonic structural relaxation expected from the Kohlrausch–Williams–Watts (KWW) model, the rejuvenated samples exhibited pronounced oscillatory relaxation during subsequent isothermal annealing. Applying a hydrostatic pressure of approximately 2GPa temporarily restored a KWW-like relaxation response; however, oscillatory relaxation gradually re-emerged after pressure-assisted activation, demonstrating that the anomalous relaxation kinetics are an intrinsic consequence of the rejuvenated structural state rather than incomplete structural recovery.,These findings establish an atomistic link between cryogenic rejuvenation, the evolution of the potential energy landscape, and oscillatory post-rejuvenation relaxation. The simulations provide a mechanistic interpretation of our previously reported experimental observations by demonstrating that the anomalous relaxation originates from repeated transitions among neighboring metastable energy minima. This work advances the fundamental understanding of the long-term stability of rejuvenated metallic glasses and provides new insights for designing thermally tailored processing strategies for high-performance amorphous alloys.

High magnetic permeability and low power loss are critical requirements for amorphous soft magnetic composites in high-frequency electronics. They are also typically mutually exclusive; low power loss requires insulating interfaces between magnetic particles, but conventional insulating interfaces cause magnetic dilution and decoupling, reducing permeability. Here, we introduce an interfacial spin-order engineering strategy that departs from traditional ferromagnetic interface solutions. By exploiting a thermally-electrically activated oxygen migration process, we construct a gradient oxygen-deficient functional layer between heterogeneous interfaces, enabling atomic-scale control of interfacial spin configurations. This engineered interface leads to a 150% increase in magnetic permeability and a 76% reduction in power loss, outperforming state-of-the-art counterparts. Neutron dark-field imaging provides direct, bulk-sensitive evidence that oxygen-defect-mediated spin ordering induces enlarged magnetic domains with intergranular magnetic connectivity. Mechanistically, defect-mediated super-exchange interactions reverse the spin orientation of Ce and Fe atoms at the heterointerface, transforming disordered or antiferromagnetic alignment into ferromagnetic coupling and thereby eliminating magnetic coupling barriers across particles. Our work demonstrates interfacial spin-ordering as a generalizable design principle, mitigating the long-standing permeability-loss trade-off.

This study investigates the relaxation kinetics of Zr₄₆Cu₄₆Al₈ bulk metallic glass (BMG) over a 30-day period following rejuvenation induced by cryogenic thermal cycling (CTC). Rejuvenation was verified by differential scanning calorimetry (DSC), which revealed an increase in stored enthalpy (ΔHrel), together with structural modifications identified by pair distribution function (PDF) analysis and positron annihilation spectroscopy (PAS). These observations confirm that CTC promotes rejuvenation in BMGs by redistributing free volume and destabilizing local atomic configurations.,Subsequent room-temperature relaxation exhibited non-Kohlrausch–Williams–Watts (non-KWW) kinetics, deviating from conventional aging models. A distinct secondary relaxation maximum appeared after 3–4 days, which is attributed to a memory-like effect associated with stress-assisted atomic reconfiguration during pre-treatment annealing. This phenomenon parallels relaxation oscillations observed in shape-memory metallic glasses, suggesting the persistence of rejuvenation-induced structural heterogeneity.,Overall, the results elucidate the dynamic interplay between cryogenic rejuvenation and natural relaxation, providing new insight into metastable state evolution and offering a pathway toward tailoring the kinetic stability of bulk metallic glasses.

The absence of periodic atomic arrangement makes it difficult to detect microscopic defects in metallic glasses, yet their roles in macroscopic shape change are prominent. Motivated by probing defects mechanically, we perform stepwise tensile creep at ambient temperature on as-spun metallic-glass ribbons that show structural anisotropy in selected area electron diffraction. The main discovery is a non-linear strain response in which the segmentally added stress causes the creep strain to initially decrease before increasing. Some strain components quickly revert after stress removal when cyclic creep is conducted, but others do not. Only the first cycle exhibits this slower-than-creep reversal; subsequent cycles have reversible strain components. The non-linearity and slow reversal are eliminated after annealing. No measurable relaxation-enthalpy change is detected within the present fast-differential-scanning-calorimetry sensitivity, suggesting that the low-stress response is not dominated by stored rejuvenation. Molecular-dynamics simulation replicates the strain responses under stepwise and cyclic creep, revealing different non-affine responses of atoms at low and high stresses. The observed behavior can be interpreted within a unified framework involving the depletion of a finite quenched-in shear-transformation-zone population together with the increasing contribution of stress-activated shear-transformation-zones. These results support an orientation-dependent, Schmid-like interpretation of low-stress visco-elastic creep in metallic glass ribbons.

Metals and ceramics have contrasting limitations—metals exhibit lower strength and poor high-temperature stability, whereas ceramics are inherently brittle. Materials combining high strength, fracture toughness and thermal stability remain an important scientific objective. Here we report Re–Co–Ta–B bulk metallic glasses (BMGs) that overcome this fundamental limitation, achieving a remarkable fracture strength of about 6.43 GPa while maintaining around 30 MPa m^1/2 fracture toughness. This strength value exceeds previously reported values for BMGs and crystalline metals and approaches the strength of advanced ceramics while far exceeding them in toughness. These alloys exhibit pronounced resistance to thermal softening and harsh environments, retaining a strength of 4.4 GPa at 900 K with negligible oxidation and corrosion. Synchrotron measurements and aberration-corrected microscopy reveal the origin of these properties: a unique amorphous structure that inherits a high degree of crystal-like short-range order from the Re₇B₃ intermetallic phase. First-principles calculations indicate that this atomic framework is strengthened by directional Re–B covalent bonds embedded in a metallic matrix, thereby bridging the ceramic and metallic bonding. This work suggests structural heredity as a guiding principle for engineering next-generation amorphous materials with previously unattainable property combinations.

Single-element amorphous metals are ideal model systems for understanding glass formation, yet their creation remains extremely challenging due to their strong crystallization tendencies. Here, we introduce a previously unexplored bottom-up route for synthesizing amorphous silver nanostructures under ambient conditions using a DNA origami template with near-fivefold symmetry. The polyanionic DNA scaffold selectively concentrates Ag ⁺ ions, which are subsequently reduced in situ to trigger localized nucleation. Importantly, the pentagonal geometry imposes strong spatial confinement and geometric frustration, providing an effective and experimentally validated mechanism for suppressing crystallization in a monatomic metal. Transmission electron microscopy confirms the formation of stable amorphous Ag domains near the symmetry center, while molecular dynamics simulations show that fivefold symmetry increases the information entropy and inhibits long-range order. This work demonstrates the first DNA-templated strategy for producing monometallic amorphous nanostructures and provides direct evidence that geometric symmetry can be used to induce amorphization in crystallization-prone metals. The resulting platform offers a powerful model system for probing amorphization mechanisms and expands the design space for structural control in nanoscale metals.

The ultra-slow relaxation dynamics of glasses at ambient temperature provide a promising alternative for dating glasses with extremely low isotopic content that cannot be dated using traditional radiometric methods. However, these ultra-slow, nonlinear aging dynamics remain poorly understood due to the lack of accurate theoretical models and long-term experimental validation. Existing equilibrium-based dynamics models substantially overestimate relaxation times at temperatures far below the glass transition temperature, making it difficult to model and quantify non-equilibrium aging over geological timescales. We address this challenge by formulating an empirical equation that quantifies the non-equilibrium effective relaxation time (τ_eff) for various glasses, including metallic glasses, organic amber, and lunar glasses. Our findings demonstrate a universal nonlinear aging dynamics governed by a single τ_eff, which follows a robust empirical relation parameterized by aging temperature and material-specific fragility. Employing this equation, we propose a universal glass kinetics dating method, conceptually analogous to radioactive decay, where τ_eff serves as a material-specific decay constant. This approach enables dating of glassy materials over timescales spanning decades to billions of years. This work bridges a fundamental gap in glass aging theory and establishes a practical framework for dating geological and planetary glasses.

The drive for high-efficiency, high-power-density power electronics in emerging technologies such as 5th generation mobile networks (5G) and artificial intelligence (AI) is impeded by a fundamental challenge in soft magnetic materials (SMMs): the intrinsic trade-off between high saturation magnetization ( B _s ) and low coercivity ( H _c ). Conventional approaches like thermal annealing rely on stochastic nucleation and growth, and thus struggle to precisely control nanocrystal size and distribution at the sub-10-nm scale, which is essential for simultaneously optimizing both properties. Here, we report a study on achieving performance breakthroughs in the Fe-(Co)-Si-B-Cu-Nb and Fe-Co-B-P alloy systems through a rotational magnetic field annealing process. This process significantly enhances the nucleation density by introducing dynamic structural fluctuations in the amorphous precursor, while simultaneously inhibiting grain growth. As a result, ultrafine nanocrystalline structures with an average grain size of only 1 ~ 5 nanometers and uniformly distributed in the amorphous matrix were successfully prepared. The obtained materials maintained an extremely high coercivity ( B _s ) of up to 1.94 T while achieving a coercivity ( H _c ) as low as approximately 0.8 A/m. This combined performance far exceeds that of existing soft magnetic materials. Computational simulations confirmed that the rotational magnetic field induced spatially non-uniform dynamic and structural fluctuations in the amorphous solid, thereby creating high-density and uniform heterogeneous nucleation sites. This work not only demonstrates a new paradigm for obtaining ultrafine nanocomposite structures through external field dynamics to control the crystallization path, but also provides a new design strategy for achieving high-performance soft magnetic materials beyond traditional performance limits, laying the material foundation for the next generation of efficient power electronic technologies.