[en] The non-isothermal crystallization kinetics and glass-forming ability of Ti₄₁Zr₂₅Be₂₈Fe₆ glassy alloy were investigated by differential scanning calorimetry. The activation energies corresponding to the characteristic temperatures have been calculated by Kissinger and Ozawa equations. Based on Kissinger-Akahira-Sunose and Ozawa-Flynn-Wall models, it has been found that the local activation energy is higher at the beginning of the crystallization process for the first exothermic peak. The local Avrami exponent indicates that the first-step crystallization is mainly a high-dimensional nucleation and growth with an increasing nucleation rate. According to the calculated fragility index, Ti₄₁Zr₂₅Be₂₈Fe₆ alloy can be classified as ''strong glass former.'' The studied alloy also possesses a critical size up to centimeter order, and the high glass-forming ability is probably related to the relatively low Gibbs energy difference between the liquid and crystalline states. The critical cooling rate of Ti₄₁Zr₂₅Be₂₈Fe₆ glassy alloy has also been determined using Barandiaran-Colmenero's method. (orig.)

[en] Shear bands, the main plastic strain carrier in metallic glasses, are severely deformed regions often considered as disordered and featureless. Here we report the observations of a sandwich-like heterogeneous structure inside shear bands in Pd_40.5Ni_40.5P₁₉ metallic glass sample after plastic deformation by high-resolution transmission electron microscopy. The experimental results suggest a two-step plastic deformation mechanism with corresponding microstructure evolution at atomic scale, which may intimately connected to the stability of the shear band propagation and the overall plastic deformability

[en] Recently, amorphous magnetic semiconductors as a new family of magnetic semiconductors have been developed by oxidizing ferromagnetic amorphous metals/alloys. Intriguingly, tuning the relative atomic ratios of Co and Fe in a Co-Fe-Ta-B-O system leads to the formation of an intrinsic magnetic semiconductor. Starting from high Curie-temperature amorphous ferromagnets, these amorphous magnetic semiconductors show Curie temperatures well above room temperature. Among them, one typical example is a p-type Co_28.6Fe_12.4Ta_4.3B_8.7O₄₆ magnetic semiconductor, which has an optical bandgap of ∼2.4 eV, room-temperature saturation magnetization of ∼433 emu/cm³, and the Curie temperature above 600 K. The amorphous Co_28.6Fe_12.4Ta_4.3B_8.7O₄₆ magnetic semiconductor can be integrated with n-type Si to form p–n heterojunctions with a threshold voltage of ∼1.6 V, validating its p-type semiconducting character. Furthermore, the demonstration of electric field control of its room-temperature ferromagnetism reflects the interplay between the electricity and ferromagnetism in this material. It is suggested that the carrier density, ferromagnetism and conduction type of an intrinsic magnetic semiconductor are controllable by means of an electric field effect. These findings may pave a new way to realize magnetic semiconductor-based spintronic devices that work at room temperature. (paper)

[en] The influence of cooling rate on the hardness of the as-prepared Pd₈₁Si₁₉ binary glassy alloys has been studied. It has been found that decreasing the employed cooling rate would increase the hardness and decrease the full width at half maximum (FWHM) of their X-ray diffractometry (XRD) spectrum. The microhardness of the bulk glassy alloy prepared by air cooling is about 453.9 kg/mm², 41% higher than that of the rapid solidified glassy ribbons. Through careful investigation of the FWHM of the XRD spectrum and the high resolution transmission electron microscope images, the cooling rate dependence of hardness is suggested to be attributed to the difference in structural uniformity and the resulted local ordering atomic clusters (medium-range order (MRO) regions) within the as-prepared glassy samples. Moreover, it has been found that decreasing cooling rate would promote the formation of denser atomic configuration and the local ordering clusters (MRO)

[en] Highlights: • Electric-field control of the room-temperature ferromagnetism has been realized in a ferromagnetic amorphous alloy. • At high magnetic fields, the amorphous ferromagnet exhibits positive magnetoresistance with weak temperature dependence. • The spin-polarized conduction electrons cause the electric-field control of ferromagnetism and positive magnetoresistance. We report the formation of a ferromagnetic Co_55.0Fe_24.5Ta_0.1B_20.4 amorphous alloy by magnetron sputtering, which exhibits positive magnetoresistance without saturation even in very high magnetic fields. This suggests that the s-like electrons responsible for the electrical conduction are spin-polarized through s-d hybridization. Owing to the electromagnetic interplay of the spin-polarized conduction electrons with the local magnetic moments, the electric-field control of room-temperature ferromagnetism is realized in the amorphous alloy. Our results offer insights for exploring the multi-functionalities of ferromagnetic amorphous alloys and extending their applications to a wide variety of electronics including magnetic tunnel junctions and compact disks.

[en] Highlights: • MG/TPE composites are produced by introducing MG powders into a TPE polymer. • The MG/TPE composites have the characteristics of both the MG and TPE materials. • The MG particles can effectively improve the wear resistance of the TPE matrix. Thermoplastic elastomers (TPEs) and metallic glasses (MGs), both lack of long-range ordering structure, have different physical and mechanical properties. To combine unique viscoelasticity of elastomers and excellent wear resistance of MGs, we propose to introduce a Pd₄₀Ni₄₀Si₄P₁₆ MG into a commercial styrene-butadiene-styrene (SBS) TPE to form MG/TPE composites. Serving as a hard and strong second phase dispersed in the SBS matrix, the micrometer-sized MG particles can effectively improve the wear resistance of the matrix due to a strengthening effect. In particular, the MG/TPE composite with an addition of 60 wt% MG shows significantly enhanced wear resistance up to about three times that of the SBS matrix. The present results provide a new way to enhance the wear resistance of the widely used TPEs, which may generate immense economic value by extending their service life.

[en] Highlights: • Ti-Zr-Hf-Cu-Ni high-entropy metallic glass thin films (HEMG-TFs) were deposited. • The HEMG-TF has the largest strain rate sensitivity of hardness in metallic glasses. • This suggests the HEMG-TF has a more homogeneously disordered amorphous structure. Quinary Ti-Zr-Hf-Cu-Ni high-entropy metallic glass thin films were produced by magnetron sputter deposition. Nanoindentation tests indicate that the deposited film exhibits a relatively large hardness of 10.4±0.6 GPa and a high elastic modulus of 131±11 GPa under the strain rate of 0.5 s⁻¹. Specifically, the strain rate sensitivity of hardness measured for the thin film is 0.05, the highest value reported for metallic glasses so far. Such high strain rate sensitivity of hardness is likely due to the high-entropy effect which stabilizes the amorphous structure with enhanced homogeneity.

[en] We report that an approximant phase was initially obtained in amorphous Ti₄₀Zr₂₀Hf₂₀Pd₂₀ alloy. In the initial stage of the devitrification process, the approximant phase transforms into an icosahedral (I) phase with a high thermal stability while the cF96 Zr₂Ni-type (space group Fd3-bar m with a=1.25nm and 96 atoms cell^-1) particles precipitate from the amorphous matrix. Eventually the I phase grows to several hundred nanometers when annealed at about 1000K and then transforms into the Zr₂Ni-type phase with an endothermic reaction

[en] Highlights: • The NPS is synthesized as an efficient ORR catalyst by an anodization-electroreduction method. • The enhanced ORR performance of NPS is investigated by experiments and DFT calculations. • The in-situ regeneration is showed as a novel strategy to extend the service life of ORR catalysts. -- Abstract: Oxygen reduction reaction (ORR) plays a major role in the efficient operation of many important electrochemical energy devices. Herein, a novel catalyst of nanoporous silver (NPS) is in-situ synthesized by a high voltage anodization method in 0.1 M KOH which also serves as the electrolyte for the catalysis of ORR. Favored by the continuous pore channels, the mass transfer is enhanced within the NPS. Theoretical calculations suggest that the strengthened interactions between OOH intermediates and the dominant Ag(110) surfaces on NPS as revealed by an adsorption test reduce the activation energy for the rate determining step and thus accelerate the ORR. Due to the enhanced mass transfer and facile kinetics, the NPS exhibits excellent ORR activity and even outperforms the commercial Pt/C. Fascinating more, the service life of NPS is significantly extended through an in-situ regeneration process. The integration concept we demonstrate in this work shed new lights on the preparation of long-life functional materials with high performance in applications including but not limited to ORR.

[en] Highlights: • A strategy for designing ductile metallic glass composites by forming nanocrystals in the high-entropy alloy particles during deformation was proposed. • The ex situ high-entropy alloy particle toughened Zr-based metallic glass composites were prepared by spark plasma sintering. • By adding CoCrFeNiAl high-entropy alloy particles, the Zr-based metallic glass composites exhibit enhanced strength-ductility synergy. • The toughening mechanisms were discussed in accordance with experiments and modeling. In this work, we prepared equiatomic AlCoCrFeNi high-entropy alloy (HEA)-particle-toughened, Zr-based metallic glass composites by spark plasma sintering. By adding HEA particles as the second phase, the strength and plasticity of the Zr-based metallic glass composites improved concomitantly. After fracture, high-density dislocations and nanocrystals were formed in the HEA particles due to local severe plastic deformation, which consumed massive strain energy to enable the resistance to crack formation. Substantial lattice distortion imparted a remarkable work-hardening capacity to the HEAs and enhanced crack-tip dislocation trapping, and thus led to an extreme refinement of the grain size. Finite-element analyses indicated that the strain hardening behavior of HEA particles reduced the magnitude of strain localization, promoted generation of multiple shear bands, and stabilized shear band propagation. We attribute the enhanced strength-ductility synergy in the current composites to high-density dislocations and nanocrystal formation in the HEA particles, and stable propagation of multiple shear bands.