Journal of Non-crystalline Solids最新文献

In this study, a metallic glass sample with an annular indentation notch was successfully constructed by a compression rod cyclic compression strategy using molecular dynamics simulation, and the mechanical behaviors of cut-notched metallic glass samples with the same stress triaxiality and notch size under triaxial compression were comparatively analyzed. It is found that the indentation notch further improves the strength and plasticity of the metallic glass, while it is insensitive to the cut-notched metallic glass with the same notch size. During triaxial compression, rejuvenation and shear softening lead to an increase in free volume, while diffusion and residual compressive stresses lead to a decrease in free volume. The stress triaxiality plays a key regulatory role in their competition and affects the final state of free volume change. This study provides a new theoretical basis and process idea for the enhancement of strength and plasticity of metallic glass.

We fabricated the Fe-Co-Ni-Si-B multi-principal element alloys by vacuum melt-spinning method. The effects of late transition metals proportion in quinary alloy ribbons on the formation, phase structure, thermal stability, microhardness, corrosion resistance and soft magnetic properties were investigated. The melt-spun structure consists of an amorphous single phase for all the specimens. The surfaces of glassy ribbons are rather flat and flawless and the average surface roughness is 0.351 nm or below. The initial crystallization temperature (T_x) and supercooled liquid region (ΔT_x) of alloy system decrease by degrees with increasing Co and Ni content, showing the maximum values of 753.0 K and 60.0 K for Fe₆₀Co₁₀Ni₁₀Si₆B₁₄ alloy. But the glass transition temperature (T_g) seems to barely change and maintain approximately 692.0 K. All the as-received alloy ribbons exhibit good bending ductility and acceptable Vickers microhardness ranging from 671 to 785 HV_0.5. The amorphous alloy ribbons present a gradually wide passive potential range (ΔE) with the decrease of Fe content, but the corrosion current density (I_corr) becomes larger. The smallest I_corr value is 1.785 μA·cm^-2 for Fe₆₀Co₁₀Ni₁₀Si₆B₁₄ alloy and the widest ΔE value is about 0.272 V for Fe₂₆Co₂₇Ni₂₇Si₆B₁₄ alloy. The saturation magnetization of these glassy alloys reduces from 165.0 to 112.0 emu/g as the Fe content decreases. Meanwhile, the coercivity also changes from 14.25 to 6.70 A/m. This paper offers a brand-new perspective to understand the role of late transition metals on the various physicochemical properties of quinary Fe-Co-Ni-Si-B amorphous alloys.

Fe-based amorphous alloys have received much attention in the fields of electronics and electrical due to their excellent soft magnetic properties at high frequency. However, the controllable preparation of large-sized Fe-based bulk metallic glasses (BMGs) still faces numerous challenges. In this study, FeSiBCCr amorphous powders prepared by gas-water combined atomization were used as raw materials, and FeSiBCCr BMGs were prepared through spark plasma sintering (SPS) at different pressures. The microstructure, phase and magnetic properties of the compacts were systematically characterized using SEM, XRD, TEM, DSC, and VSM. The results showed that when the sintering pressure was 50 MPa, the slow densification process dominated by particle rearrangement at the initial densification process made the internal contact resistance of the compacts larger. This led to macroscopic inhomogeneous physical fields and severe local overheating during the later stages of sintering, causing the precipitation of α-(Fe, Si) and Fe₃B phases. Although the material exhibited a relatively high saturation magnetization (B_s) of 1.08 ± 0.01 T, the low density and amorphous fraction resulted in a high coercivity (H_c) of 1060.8 ± 37.8 A·m^-1. When the sintering pressure was increased to 250 MPa, the degree of particle densification significantly improved, and the temperature inhomogeneity was markedly suppressed due to reduced internal resistance. Thus, the prepared FeSiBCCr BMGs exhibited an extremely high density of 6.66 ± 0.06 g·cm^-3 and excellent soft magnetic properties with B_s of 1.23 ± 0.01 T and H_c of 18.8 ± 1.8 A·m^-1. This indicated that the FeSiBCCr BMGs prepared in this study exhibited broad application prospects in efficient electromagnetic conversion and advanced electronic devices.

Nanoimprint is a low-cost and effective method to manufacture nanostructures for metallic glasses with a precision replication of the mould shape and control of size. However, the atomic structure of the materials changes during the processing, which affects the practical application and the performance of the nanostructures. This crucial issue has not been addressed as thoroughly as it deserves. Here, we investigate the rheological behaviors of metallic glasses under the deformation with different temperatures and strain rates via molecular dynamic simulation. We find an abnormal rheological mode change in the non-Newtonian region, which is attributed to the evolution of short- and medium-range ordered structures. Mechanical deformation leads to the destruction and regeneration of atomic short-range ordered structures at all strain rate ranges. Their total amount and distribution remain at a similar level when the strain rate is low. When the strain rate exceeds a critical value, the deformation accelerates the relaxation by shortening the β-relaxation, resulting in the decrease of the total amount of short-range ordered structure and reorganization in the medium-range ordered structure. Furthermore, the results show a significant inheritability from the sample during deformation to the cooled-down sample, demonstrating the influence of deformation history on the properties of materials manufactured with the nanoimprint. The deformation during the nanoimprinting could reduce the ultimate strength and increase the plasticity of the materials, which provides a potential method to precisely turn the properties of metallic glasses by controlling the rheological process in the nanoimprint possessing.

The present research, reports the hygrothermal behavior of poly [ethylene oxide] (PEO) based composite film (500 and1000 μm) containing NH₄I and KBr (5–20 wt%) as the mobile phase and non-reactive silica (15 wt%) as the filler. These are termed as PK/NSiO₂-series for solvent sorbed and (PK/NSiO₂)_NS for non-swelled film. The novelty of the research lies in the analyses of non-Fickian solvent diffusion trait of films using python programming. The presence of ions and its variable polarizable nature is found to influence the number density of bonded and free solvent content along with the extend of cross linkage. Introduction of silica is found to enhance the ionic conductivity (about one order higher) of the film irrespective of the type of charge carrier owing to the improved dispersion within the matrix. Non-Fickian diffusion is found to influence the ionic conductivity of P₂K20SiO₂ (10⁻⁵Scm⁻¹ to 10⁻² Scm⁻¹) minimizing the degradation to 0.2 %ΔC/1000 h (>1 %ΔC/1000 h, tested for 2000 h) compared to P₂N20NSiO₂. In contrast, ion migration in P₂NSiO₂ is guided by Rice and Roth model and being more polarizable ions, the mobility is significant which maximizes the conductivity to ∼10⁻¹ Scm⁻¹. Microstructural study shows heterogenous nucleation to be more pronounced upon addition of silica filler wherein the homogeneity, inter fibrillar interaction and grain growth of spherulites is higher. This tends to extend amorphous regions thereby propagating the ion migration path. The influence of sorption process is studied in terms of electrochemical impedance, dielectric analyses and long term cyclability (20,000 h) in terms of loss tangent.

The organic glass-forming dibutyl phthalate (DBP) has been studied applying low-frequency Raman and Brillouin spectroscopy in the temperature range from 90 K to 200 K, covering glassy and liquid states. Spectra of fast relaxation in the GHz-THz frequency range were determined from the inelastic light scattering spectra. The line width and position of the Brillouin peak were used to determine the Q^-1-factor, which is inversely proportional to susceptibility at the Brillouin peak frequency. It was discovered that the temperature evolution of the fast relaxation susceptibility and the Q^-1-factor agree well with a mobility parameter from pulse EPR experiment. The findings show that peculiarities in the temperature dependence the EPR data found early for DBP have are accompanied by a redistribution of the relaxation times.

In this paper, a range of sputtered ternary and quaternary (Si)(Ge)As${}_x$Te${}_3$ layers (x: 2 or 5) and (Si)(Ge)As${}_2$Se${}_3$ layers are examined using Raman spectroscopy. The results are linked to the Ovonic Threshold Switching properties of these materials when incorporated in selector devices, as observed in separate studies. In case of both the As-rich and As-poor tellurides, a large amount of homopolar bonds are present as the spectra are dominated by peaks associated with As–As and Te–Te bonds. Such homopolar bonds are commonly linked with drift in OTS properties. In the case of the selenides the spectra are dominated by modes associated with heteropolar As–Se bond vibrations. Adding Ge as an alloying element has a significant impact on the bond structure for both material systems. In contrast, Si has a much less pronounced impact and will mostly bond with itself. Time-resolved Raman measurements were also performed to determine the stability of the layers under micro-Raman laser excitation. At the regular exposure settings, no significant changes in the spectra were observed during the measurement. At elevated exposure settings, however, persistent changes in the bond structure can be induced for certain compositions.

The issue of crystallization during the laser cladding process poses a significant challenge to the application of amorphous coatings. In order to explore the practical application of Fe_41.5Co_12.2Cr_7.4Mo_37.3C_0.3B_0.5Y_0.4Al_0.4 (at.%) amorphous composite coatings, this study fabricated coatings with different scanning speeds. The aim was to delve into their crystallization processes and assess the consequential effects on the coatings’ properties. The study revealed that crystallization predominantly occurs in the coatings’ overlapping region, which can be divided into two zones: the overlapping transition zone (OTZ) and the overlapping heat affected zone (OHAZ). The crystallization extent within the OHAZ is higher than in the OTZ, attributable to the disparate cooling rates characteristic of each region. With increasing scanning speed, the OHAZ gradually increases and the OTZ decreases. The coating prepared at 2000 mm/min has excellent corrosion resistance (polarization resistance 10,814.2 Ω$·$cm²) and wear resistance (wear rate (8.88$\pm$0.378)$\times$10^–6 mm³/N$·$m).

This study investigates the behaviour of As₂₀Se₈₀ and Ge₂₅Se₇₅ chalcogenide glasses near the glass transition temperature using differential scanning calorimetry (DSC) and thermomechanical analysis (TMA), addressing a gap in the literature for these compositions. Precise TMA measurements of viscosity in the range of 10⁶ – 10¹³ Pa·s clarified existing data and improved the quality of fits describing the temperature-dependent viscosity for both compositions. The DSC method enabled a comprehensive analysis of structural relaxation behaviours, which were described using the Tool-Narayanaswamy-Moynihan (TNM) model with the determination of its four parameters. The study discusses the viscosity and structural relaxation behaviours of both glass-formers in relation to their structure, referencing previous results for other binary chalcogenide glasses in the As-Se and Ge-Se systems. The findings indicate significant changes in viscosity and activation energy of structural relaxation with the addition of As or Ge, while the non-linearity and non-exponentiality parameters remain largely unaffected.

Different heating conditions markedly affected the competing processes of densification and crystallization of bioactive glass (BAG) S53P4 powder compacts. BAG S53P4, known for its osteostimulative and bacterial growth-inhibiting properties, is a promising material for 3D scaffolds for bone repair and tissue engineering. However, due to its crystallization tendency, the impact of different heat treatments on the glass's sinterability must be better understood. The densification and crystallization of S53P4 powder (<45 µm) compacts were systematically investigated in air under various isothermal and non-isothermal conditions. Heating microscopy and SEM morphological analysis provided detailed maps of time- and temperature-dependent densification and surface crystallization. Suitable parameter ranges for isothermal sintering were determined. Using an initial heating rate of 20 °C min⁻¹ and temperatures of 600–615 °C, amorphous compacts showing moderate densification (ρ_rel ≈ 77 %) were achieved. Longer treatments led to higher densification (ρ_rel ≥ 84 %) but also caused crystallization, resulting in glass-ceramic products.