Journal of Non-crystalline Solids最新文献

The evolution of structure and physical properties was investigated in the (Ag₂S)_x(HgS)_50-x(GeS₂)₅₀ system. It was found that the density increases with increasing silver sulfide. The DSC data show a non-monotonic change of the glass transition temperature, T_g, from 243 °C (x = 0) to 301 °C (x = 50) with the minimum at 231 °C for x = 10 sample. The dual structure of HgS, which consists of the presence of dimorphic tetrahedral and chain forms of HgS, is found to be responsible for the non-monotonic change of the T_g. An increase in silver content leads to a significant enhancement of ionic conductivity from ∼10⁻¹⁴ S.cm⁻¹ (x = 0) to ∼10⁻³ S.cm⁻¹ (x = 50). The gradual structural evaluation is evidenced by the disappearance of the main Raman feature at ≈300 cm⁻¹ related to the Hg-S stretching and the emergence of two contributions for silver-rich glasses at ≈370 cm⁻¹ and at ≈400 cm⁻¹.

Bulk metallic glasses (BMGs) show limited plasticity at room temperature. However, BMGs usually exhibit superplasticity and high plastic forming ability in their supercooled liquid region (SLR). The rheological behavior of BMGs in SLR is vitally important to their thermoplastic forming process. In contrast to the ductile BMGs, thermoplastic deformation behavior of brittle BMGs is rarely reported. In present work, the rheological behavior of two brittle BMGs with high glass forming ability Cu_44.25Ag_14.75Zr₃₆Ti₅ and Ti_32.8Zr_30.2Cu₉Ni_5.3Be_22.7 was investigated on Gleeble3500. The two BMGs can deform homogeneously depending on the temperature and strain rate. According to the high value of m (strain rate sensitivity index), which is the most important mechanical characteristic of a superplastic material, the two BMGs show superplasticity in their SLR with m ≥ 0.3. Based on the free volume model, their activation volumes are calculated as 0.263∼0.486 nm³ and 1.261∼1.650 nm³, indicating the minimum displacement clusters with average 26∼48 and 91∼127 atoms, for Cu_44.25Ag_14.75Zr₃₆Ti₅ and Ti_32.8Zr_30.2Cu₉Ni_5.3Be_22.7, respectively. Thus, the two investigated brittle BMGs can be thermoplastic processed in the SLR and the deformation maps are given. BMG Cu_44.25Ag_14.75Zr₃₆Ti₅ shows better machinable property than Ti_32.8Zr_30.2Cu₉Ni_5.3Be_22.7. Compared to the ductile BMGs, no Newtonian flow is found for the two investigated brittle BMGs.

A viscosity model based on CALPHAD principles, considering the influences of associates in multicomponent melts, was developed. A strategy for determining CALPHAD-type viscosity parameters in systems lacking experimental data was proposed, which combines the Kozlov-Romanov-Petrov model and thermodynamic descriptions. This model and strategy were applied to analyze viscosities in Mg-Al-Zn-Sn-Bi melts. The viscosity expressions of pure melts were initially assessed based on the available experimental data. Subsequently, the Arrhenius viscosities of Mg₃Bi₂, Mg₂Sn, and MgZn₂ associates were determined by integrating thermal-physical properties into Kaptay equation. Viscosity parameters for 10 sub-binary and sub-ternary systems within Mg-Al-Zn-Sn-Bi system were examined. A comparison between predicted and measured viscosities confirmed the accuracy of the model. Isothermal viscosities in all sub-ternary melts were calculated to assess the impact of alloying elements on viscosity. Additionally, viscosities in AZ91 alloys with Bi and Sn additions were predicted, demonstrating an increase in viscosity with higher Bi or Sn content.

Glasses in the system BaO – La₂O₃ – Ga₂O₃ – GeO₂ and Langasite crystalline phases with the same stoichiometry have been studied considering the possible use of these glasses for laser-induced space-selective growth of crystalline architectures in the glass compositions. For better understanding of mechanisms involved in such controlled crystallization process, crystalline and glass compounds with same stoichiometry and different La/Ba ratios have been synthesized to compare their local structure. Solid-state Nuclear Magnetic Resonance evidence 4- and 5-coordinated gallium units in the glass matrix, denying unambiguously the formation of 6-coordinated gallium sites observed in crystalline phases. Moreover vibrational spectroscopies suggest a link between a 3D network formed by 4- and 5-coordinated gallium, connected to each other and to 4- coordinated Q4 and Q3 germanium units in the glass and their congruent crystallization. The transition from 4- and 5-coordinated gallium to 6-coordinated gallium sites observed in Langasite crystalline phases remains not still elucidated.

Combined with the pendant drop method and infrared and Raman spectroscopic detection, the effect of the basicity on the density and surface tension properties and the structure of CaO-SiO₂–10 % Fe_xO slag was investigated. With increasing basicity from 0.5 to 1, it is found that the density and surface tension values increase at the same temperature. Meanwhile, the complex structures of Si-O groups in the slag depolymerize, the area proportion of [FeO₆]^9- units decreases from 13.0 % to 8.3 % and that of [FeO₄]^5- units increases significantly from 2.9 % to 18.6 %. The key factor determining the area proportion and structural evolution of [FeO₆]^9- and [FeO₄]^5- units is the basicity rather than the relative contents of Fe²⁺ and Fe³⁺ ions. Overall, the slag polymerization degree depends on the structures of Si-O groups rather than on those of Fe-O groups, which leads to increases in the density and surface tension with increasing basicity.

Developing low-cost, and efficient oxygen evolution reaction (OER) electrodes with high flexibility is critical for hydrogen production. Here, flexible noble-metal-free Fe-based metallic glassy OER electrodes were fabricated via an electrochemical dealloying method combined with a dipping process. The sample requires a low overpotential of 258 mV to achieve a current density of 10 mA cm⁻² in 1 M KOH solution, and the Tafel slope is 51.7 mV/dec. Galvanostatic test proved the excellent electrochemical stability of the electrodes. The highly efficient performance mainly originated from the high-energy disordered amorphous microstructure combined with the doping effect of nickel. Furthermore, the unique double-layer structure of the nanoporous surface covered with amorphous sheets increased the contact area of the samples. The ductile amorphous matrix together with the amorphous sheets tightly bonded on the nanoporous layer results in high flexibility of the electrodes. Our work provides a simple strategy to fabricate flexible amorphous OER electrodes.

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.