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The underlying structural origin of magnetic properties is still elusive in Fe-based amorphous alloys. In this study, distinctive soft magnetic properties were developed in Fe76Si9B10P5 amorphous ribbons through systematic design of annealing process. Combining with synchrotron radiation, high-resolution transmission electron microscopy and first principle ab initio molecular dynamic simulation, it is found that the atomic structural evolution both in short range order and medium range order is responsible for the magnetic softness at proper annealing temperature. In short range, formation of separated and densely coordinated Fe-metalloid clusters is instigated to adapt energy minimization, resulting in strengthening of ferromagnetic exchange interaction locally. In medium range, a homogeneous exchange-coupling from the uniformly strong and weak ferromagnetic regions is generated, which significantly weakens magnetic heterogeneity and leads to the excellent magnetic softness. Our findings may provide an effective/promising pathway to modulate the magnetic properties for Fe-based amorphous alloys, and give a comprehensive and quantitative understanding of the structure-properties relationship in amorphous materials.

Glasses have markedly different stability around their glass transition temperature ( T g ), and metallic glasses (MGs) are conventionally regarded as metastable compared to other glasses such as silicate glass or amber. Here, we show an aging experiment on a Ce-based MG around its T g (~0.85 T g ) for more than 17 years. We find that the MG with strong fragility could transform into kinetic and thermodynamic hyperstable state after the long-term room temperature aging and exhibits strong resistance against crystallization. The achieved hyperstable state is closer to the ideal glass state compared with that of other MGs and similar to that of the million-year-aged amber, which is attributed to its strong fragility and strong resistance against nucleation. It is also observed through the asymmetrical approaching experiment that the hyperaged Ce-based MG can reach equilibrium liquid state below T g without crystallization, which supports the idea that nucleation only occurs after the completion of enthalpy relaxation.

Multilayer graphene has been employed as a functional material for tuning the emissivity in mid- and long-infrared range, which shows great potential for various applications, such as radiative cooling and thermal camouflage. However, the stability of the multilayer graphene is not sufficient for practical applications yet. Even though it is reported that the integrity of the multilayer graphene is compromised by ion intercalation, the detailed mechanism is rather unclear. Here, a set of ionic liquids is deployed as sources of electronic charges for tuning the emissivity of multilayer graphene. It is found that the emissivity modulator using 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([EMIm]NTf2) as the ionic liquid provides a modulation depth of about 0.52 (i.e., about 21% larger than the best-reported value) while maintaining a reasonable device lifetime. The microscopic structures of the multilayer graphene in an operational and failure modulator are investigated by scanning electron microscopy, Raman spectroscopy, X-ray diffraction. The results indicate that the modulation depth of emissivity is negatively correlated with the initial voltage, which represents the reaction potential between the ionic liquid and graphene. Furthermore, not only the chemical reactivity but also the size of both anion and cation in the ionic liquids play important roles in maintaining stability of the modulator. Therefore, a set of criteria (e.g., low initial voltage and small size of anion and cation) is proposed to select proper ionic liquids for emissivity modulation. This not only sheds light on the underlying physics of the modulator but also promotes its practical applications.

Maxwell-Voigt model with two Kelvin units and one Maxwell unit was utilized to analyze the microalloying effect of Cu on the creep behavior of CoFe-based metallic glasses at different loading rates. The defect activation during creep deformation was detected by the relaxation time spectrum based on this model. The defect, with respect to a short relaxation time in relaxation spectra, intends to be activated at a quasi-static loading mode in the alloy with 0.5 at.% Cu addition. With further increasing loading rates, more defects with a large size were provoked activated at both hard and soft regions in the Cu-containing sample. A softening with the reduction of elastic modulus and hardness about 10 % and 15 %, respectively, was also observed in the Cu-doped sample. It is consistent with the pronounced viscoplastic deformation of this alloy along with the decrease of viscosity. Our work provides a microscopic insight into structural evolution during creep deformation in a Cu-doped metallic glass, which might help for understanding the plastic deformation of metallic glasses upon a minor addition.

Ultrasonic vibration can be used for the micro-molding of metallic glasses (MGs) due to stress-softening and fast surface-diffusion effects. However, the structural rearrangement under ultrasonic vibration and its impact on the mechanical response of metallic glasses remain a puzzle. In this work, the plastic flow of the Zr35Ti30Cu8.25Be26.75 metallic glass with the applied ultrasonic-vibration energy of 140 J was investigated by nanoindentation. Both Kelvin and Maxwell-Voigt models have been adopted to analyze the structural evolution during the creep deformation. The increase of the characteristic relaxation time and the peak intensity of relaxation spectra can be found in the sample after ultrasonic vibration. It effectively improves the activation energy of atomic diffusion during the glass transition ( E g) and the growth of the crystal nucleus ( E p). A more homogenous plastic deformation with a weak loading-rate sensitivity of stress exponent is observed in the ultrasonic-vibrated sample, which coincides with the low pile-up and penetration depth as shown in the cross profile of indents. The structural rearrangement under resonance actuation demonstrated in this work might help us better understand the defect-activation mechanism for the plastic flow of amorphous systems.

Nanoscaled structure inhomogeneity has been identified to be an inherent characteristic of metallic glasses (MGs). Structural heterogeneities are also found to play a key role in designing and tuning the mechanical and relaxation behavior of MGs. As one peculiar member of the glassy family, U-based MGs show novel unique properties desirable for nuclear industries. However, the heterogeneous characteristics of this type of MGs have never been studied so far. In this study, U65Fe30Al5 and U60Fe27.5Al12.5 MGs were systematically investigated with nanoindentation of high sensitivity. They exhibit significantly different mechanical response for the primary and secondary creeps at varying loading rates and peak loads. Through analysis with the theoretical creep model for viscoelastic materials, U60Fe27.5Al12.5 MG is found to be in a more rigid state for the secondary (viscous) creep, suggesting more compact atomic structure for it. By further analysis and fitting with this model, dissimilar structural heterogeneity can be derived for these two MGs to account for their difference in creeping behavior. This work manifests that nanoindentation is a very useful technique to reveal heterogeneous structures of glassy alloys, and also to establish their composition-structure-property relationship.

Fundamental issues of U-based binary metallic glasses (MGs) have been scarcely studied due to their low thermostability and glass forming ability (GFA). In this work, the glass formation in U–Ni system was reexamined. It is found that currently designed U–Ni glassy alloys in the range of 54–75% U show a pronounced thermal glass transition feature for the first time among binary U-based systems, and also have the glass transition temperature (Tg) above 600 K and much stronger thermostability than other similar U-based glasses. The Tg presence contributes to the evaluation of their glass transition activation energy, liquid fragility, viscosity as well as the Kauzmann temperature. Moreover, the fragility value of the typical alloy U69.2Ni30.8 is about 20, almost the same as those of the oxide glass formers SiO2 and GeO2, illustrating that U–Ni is a binary strong glass forming system. The reasons for the remarkable Tg presence and low fragility together with the GFA level of U-based MGs are discussed.

Steadily, continuously, and precisely adjusting infrared emissivity of materials is of great importance for various applications, such as thermal camouflage. Herein, a method is proposed to fine-tune the emissivity of multilayer graphene (MLG) by ion intercalation with assistance of pulse voltage. The dynamic ion intercalation process in MLG-based emissivity modulators is investigated by a home-made electrical-optical synchronizing test system, which consists of a potentiostat and a thermal camera. It is observed that the apparent temperature of MLG is closely correlated with pulse duration and residual charges. Based on a second-order RC model, the ion transportation and charge transfer in the modulator are likely affected by three factors (i.e., internal resistance, electric field, and concentration gradient), which changes the doping level of MLG. Hence, the emissivity of MLG can be finely adjusted by regulating the duration of the voltage pulse. This also leads to a wavelength dependence of emissivity modulation, which is confirmed by Fourier transform infrared spectroscopy. The observations offer a promising venue for precise and continuous adjustment of MLG's emissivity, which is of great significance for many practical applications, such as simulating complex and subtle thermal images.

Actively controlling the infrared emissivity of materials is critical for many applications, such as radiative cooling and thermal camouflage. Multilayer graphene (MLG) has shown great potential as a functional material with a tunable infrared emissivity. However, the spatial homogeneity in adjusting MLG's emissivity through ion intercalation is rather poor, which limits its practical applications. Here, we study how mixing various molecular components (e.g., ethanol) with ionic liquids affects the performance of MLG-based infrared emissivity modulators. The results indicate that introducing a moderate concentration of molecular components not only significantly improves spatial homogeneity in tuning emissivity but also enhances modulation depth, dynamic response, and the stability of the modulators. This is likely due to the increasing conductivity of the mixture and the improved wetting properties between the mixture and the separator, which leads to more effective charge transfer from ions in ionic liquids to carbons in graphene. The microscopic structure of MLG, revealed by Raman spectroscopy, confirms that the improvement in modulator performance is mostly due to homogeneous transportation of ions in the modulators. This not only sheds light on the underlying physics of the modulator but also greatly expands the options when selecting ionic liquids, thereby opening a new route for the modulator design.

On the basis of the grain boundary additive of Nd65Ni35 alloy with the melting temperature of 535 °C and different annealing treatment at 500 °C, 590 °C and 680 °C, respectively, a series of Nd-Fe-B based magnets with different grain boundary fine structures were produced. Their corrosion resistance is found strongly dependent on the grain boundary fine structure. A Ni-rich layer/Nd-rich layer/Ni-rich layer sandwich-structured grain boundary, in particular, contributes to the optimal anti-corrosion performance and magnetic properties for the magnet annealed at 590 °C. The results suggest that more anti-corrosive Nd-Fe-B based magnets could be fabricated by tuning their grain boundary fine structure.

The preparation of bulk U-based metallic glasses has fails for a long time due to weak glass forming ability and the low chemical purity of raw uranium metal. To make bulk glassy samples containing uranium, the compositing approach is adopted in this study. U-involved sphere-dispersed metallic glass matrix composites are successfully in-situ synthesized with suction-casting and tilt-casting by the phase separation alloying of uranium and Zr41.2Ti13.8Ni10.0Cu12.5Be22.5 (Vit-1). These composites are in a large composition range of 3–40 at.% U and with a flexible diameter dimension of not

By using Al as the third and B as the fourth but minor alloying elements for the U66.7Co33.3 basic metallic glass, a series of U-Co-Al(-B) alloys were designed. The quaternary U-Co-Al-B alloys exhibit significantly improved glass-forming ability (GFA) than previously reported U-based metallic glasses. Low fragility (∼24) is found for these new U-based metallic glasses. The improvement in GFA would result from denser atomic packing in the undercooled liquids due to the presence of small B atoms. Some U-Co-Al(-B) glasses showed corrosion resistance comparable to that of U64Co34Al2 glass, known for premium anti-corrosive performance among the unveiled U-based glasses.

Bulk metallic glass composites (BMGCs) with in-situ formed crystals can display tensile ductility at room temperature, overcoming brittleness of monolithic bulk metallic glasses (BMGs). However, the ductility and toughness of BMGCs severely deteriorate at low temperatures, which has been a longstanding bottleneck hindering their low-temperature applications. Here, the low-temperature tensile properties of two Ti-based BMGCs containing stable β-Ti crystals with dislocation-mediated plasticity (Fe1) or shape memory β-Ti crystals (Fe0) were investigated. With temperature decreasing from 298 to 77 K, the strength of Fe1 increases but its tensile ductility decreases. In comparison, the shape memory Fe0 BMGC exhibits a simultaneous enhancement of strength and tensile ductility as temperature decreases from 298 to 143 K. The superior low-temperature properties of Fe0 are attributed to its combined structure of a glassy matrix and shape memory crystals. As temperature decreasing, the glassy matrix possesses an increased strength which softens as shear bands form, and the shape memory crystals are more inclined to deformation-induced martensitic transformation. Therefore, the combination of characteristic properties of metallic glasses and shape memory crystals in shape memory BMGCs can successfully overcome the low-temperature brittleness. These findings are believed to facilitate the development of BMGCs with superior low-temperature properties and promote their applications at low temperatures.

The non-isothermal crystallization behavior of uranium-based amorphous alloy U 64 Co 28.5 Al 7.5 was investigated by using differential scanning calorimetry. Its kinetic fragility parameter, overall crystallization activation energy and Kauzmann temperature were determined to be 28, 234 kJ/mol and 580 K, respectively. The evolution of the crystallization activation energy with the volume fraction crystallized, which was established by both the Kissinger and Ozawa methods independently, suggests a typical three-staged process for the crystallization. As reflected by the change of the local Avrami exponent with the fraction crystallized, nucleation dominates the whole process that can be illustrated phenomenologically with the percolation model. This work is helpful for understanding the formation and thermal stability of U-based amorphous alloys, and also for the development of new materials of this kind.

The effect of minor Sn alloying on the glass formation of U-based alloys is investigated. A string of U-Fe alloys designed with the eutectic rule are all formed in a partially glassy state under melt-spinning. Minor addition of Sn gives rise to the full amorphisation of the alloys, and the achievement of the reduced glass transition temperature for new U-Fe-Sn alloys comparable to some ordinary bulk metallic glasses. This role of Sn microalloying may be ascribed to improved packing efficiency of icosahedral atomic clusters underlying in the alloy liquids. It is suggested that local atomic packing is a necessary consideration for exploiting desirable U-based multicomponent alloys with high glass forming ability.

A series of U-based U-Co-Al metallic glasses with greatly improved glass-forming ability and thermal stability were obtained by the alloying addition of Al into U-Co alloys. The fragility of these glasses approached 28, indicating strong liquid behavior. The corrosion resistance and mechanical hardness of the glasses were substantially enhanced in comparison with crystalline uranium materials. The roles of delocalization of 5f electrons and their bonding states are stressed in the discussion of the glass formation, thermal stability and the deviation of elastic modulus from the rule of mixtures. The finding not only adds a new member to the family of metallic glasses, but also provides a category of potentially useful uranium materials.

The crystallization behavior of Zr60Cu20Fe10Al10 amorphous alloy was studied using non-isothermal differential scanning calorimetry. The overall crystallization activation energies determined using the Kissinger and Ozawa methods were 240.9 ± 6.4 and 241.2 ± 6.0 kJ/mol, respectively. The local activation energies, which were calculated using the Ozawa–Flynn–Wall method, indicated a three-stage crystallization process. The local Avrami exponents were calculated to characterize the competition between crystallite nucleation and growth. In situ heating transmission electron microscopy observations confirmed the theoretical predictions.