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Herein, we report high magnetocaloric performance of melt-extracted metallic glass Gd 60 Al 20 Co 20 microwires, which exhibit a large and reversible magnetocaloric effect (MCE). The isothermal magnetic entropy change (−Δ S m ) reaches as high as 10.1 J kg −1 K −1 and the refrigerant capacity (RC) has a large value of 681 J kg −1 for a field change of 5 T. The as-obtained Gd-based metallic glass microwires hold a great promise for multifunctional applications in MCE-based refrigeration of liquid nitrogen temperature range. [ABSTRACT FROM AUTHOR]

Highlights: [•] High-quality Gd55Al25Co20 metallic glass magnetocalorific fibers were melt-extracted. [•] They show superior MCE performance versus its counterpart in BMGs. [•] They have tensile strength of 1189MPa and high security threshold of 796MPa. [•] The excellent performances result from size effect and amorphous structure. [Copyright &y& Elsevier]

High-purity melting is critical for casting metallic glass components, which would be achieved by developing the induction skull melting (ISM) technology used in casting process. The melting process of metallic glass components during ISM is urgently desired to be understood, which is rare so far. Based on this, a full-scale coupling simulation model for ISM technology with finite element method (FEM) was proposed, which contains all physical fields engaged in the melting processes. Furthermore, the metallic glass melting process was experimentally and numerically investigated based on the full-scale coupling model. The distribution of the multi-physics field within the charge was elaborated based on the numerical simulation results, especially electromagnetic field contribution, heat transfer, meniscus shape and melt reflux zone. Furthermore, due to its high viscosity, a long holding time to improve melt homogeneity is necessary for metallic glass melt. The chief aim of this work is to understand of induction melting process for melting amorphous master alloys using induction skull melting technology and to provide a foundation for the casting method to form bulk metallic glasses. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel hydrogen storage alloy fiber is prepared by the method of melt extraction. • Well-dispersed Mg 2 Ni nanoparticles precipitated in Mg-Ni-Ag fiber as a catalyst. • The hydrogen absorption capacity of Mg 85 Ni 14.8 Ag 0.2 fiber reaches 1.5 wt% at 50 °C. • Hydrogen transport is further promoted by micro-pores and cracks formed in fiber. The intermetallic compound Mg 2 Ni shows improved hydrogen de-/absorption kinetics and a lower desorption temperature compared to pure Mg. However, the coarse Mg 2 Ni phase and its limited hydrogenation capacity restrict the application of the Mg 2 Ni alloy. In this study, an attempt was made to prepare Mg-Ni alloy fibers with a higher Mg content and a well-distributed Mg 2 Ni catalytic phase using the melt extraction (ME) method, and a unique metallic glass fiber was formed. With pre-annealing at 350 °C in a vacuum, uniformly dispersed Mg 2 Ni nanoparticles are in-situ formed, the phase transition is revealed to be metallic glass → Mg 6 Ni → Mg 2 Ni + Mg. About 1.5 wt% of hydrogen can be absorbed by the Mg-Ni fibers at 50 °C, and it is completely released in 8.8 min at 225 °C. Both the JMA and Kissinger models were utilized to accurately characterize the dehydrogenation activation energy, and the values of 90.4 and 95.8 kJ/mol were obtained, respectively. The hydrogen desorption process involves two distinct processes, the decomposition of Mg 2 NiH 4 nanoparticles and MgH 2 hydride in sequence, with dehydrogenation enthalpy changes of 64.5 and 78.2 kJ/mol, respectively. After hydrogen absorption and desorption cycles, a loose structure forms around the Mg 2 Ni nanoparticles. This structure serves as an efficient nucleation site for hydrides and provides diffusion paths for H atoms. [ABSTRACT FROM AUTHOR]

Abstract The atomic structure evolution of Gd 36 Tb 20 Co 20 Al 24 high entropy metallic glass microwire from room to cryogenic temperature has been studied by in-situ high energy synchrotron X-ray diffraction. During the cooling process, the atomic volume decreases. For short-range order, the coordination numbers of all atomic pairs increase. As the temperature decreases, bond lengths of large atom-small atom and small atom-small atom pairs keep decreasing whereas that of large atom-large atom pairs unexpectedly increases continuously. The mechanism of atomic structure evolution is proposed, which might be helpful for better understanding the low temperature magnetocaloric effect of high entropy metallic glasses. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

• Apparent liquid-liquid transition (LLT) of several Zr-Cu-Ni-Al melts have been discovered at about 300 K above the liquidus temperature. • Two different glasses are obtained by regulating LLT in these alloys, manifesting that LLT comes from the competition between two types of atomic clusters. • LLT reconstructs the atomic structure at short-range order which was seldom verified in previous work. Up to now, the research of liquid-liquid transition (LLT) has significantly improved the understanding of its liquid structure and evolution, which is crucial to addressing the longstanding problem with glass formation. However, it remains unclear how LLT affects the vitrification and structures of glasses, due to the challenge in experimentally exploring LLT in high-temperature melt well above the liquidus temperature. In the present study, an experiment is conducted to observe LLT in three Zr-Cu-Ni-Al melts at around 1450 K from both dynamic and thermodynamic perspectives. It is discovered that superheated fragility is closely associated with glass-forming ability. By controlling the melt temperature, two types of metallic glasses are obtained, showing difference in crystallization behaviors, which is attributed to the competition between crystal-like clusters and icosahedral-like clusters. Prior to the LLT, the formation of crystal-like clusters is dominant. Afterwards, the LLT promoted formation of icosahedral-like clusters becomes dominant. Due to the inherited signatures in glass, LLT is manifested by the changes in both medium-range order structure and short-range order structure. This study further reveals the pattern of microstructural evolution accompanied by LLT in high-temperature multi-component melts, which is conducive to the control on structure and properties of glasses from liquids. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nanocrystalline Fe-containing GdTbCoAl high-entropy-metallic-glass were attained. • Curie temperature is tuned by Fe-doping in a wide temperature range of 81–108 K. • Magnetic entropy change 7.6–8.9 J kg−1 K−1 for 5 T were achieved. • The dual-phase structure with T C distribution enhances the cooling efficiency. Through designing the composition and processing approach, the non-equiatomic (Gd 36 Tb 20 Co 20 Al 24) 100-x Fe x (x = 0, 1, 2 and 3 at.%) high-entropy-metallic-glass (HE-MG) alloy microwires were successfully fabricated by melt-extraction technique. The microstructure and magnetocaloric properties of the microwires were systematically investigated. The microwires possess tunable Curie temperatures, i.e. 81–108 K, above the typical rare-earth (RE) containing HE-MG reports. The high Curie temperatures are attributed to the designed composition. Magnetocaloric response peak values of Fe-containing GdTbCoAl alloy microwires range 7.6–8.9 J kg−1 K−1 (5 T), which are comparable to those of many outstanding RE-containing magnetocaloric HE-MGs. The characteristics of the melt-extraction method, combining with compositional effects, favor the formation of amorphous and nanocrystalline phases. The increase in the cooling efficiency for microwires with higher Fe content can be attributed to the broadening of the Curie temperature distribution induced by the composition difference between nanocrystalline phase and amorphous matrix. The designed composition and the melt-extraction processing approach for Fe-containing GdTbCoAl alloys can tune their Curie temperatures towards a temperature range of natural gas liquefaction and improve their magnetocaloric properties. This demonstrates that Fe-containing GdTbCoAl HE-MG composite microwires have great potential as high-performance magnetic refrigerants. [ABSTRACT FROM AUTHOR]

The enhanced magnetocaloric properties are studied in melt-extracted Gd 36 Tb 20 Co 20 Al 24 metallic glass microwires. The Curie temperature is ∼91 K for these microwires which show promising applications at liquid nitrogen range. The microwires possess spin glass phase in low temperature and spin freezing temperature is 60 K. Notably, the maximum magnetic entropy change (–Δ S M max), the relative cooling power (RCP) and the refrigerant capacity (RC) reach high values of 12.36 J kg−1K−1, 948 J kg−1 and 731 J kg−1, respectively, under a field change of 5 T. The large –Δ S M max originates from the high effective magnetic moment. Meanwhile, the spin fluctuation, the exchange integral fluctuation of metallic glass and the second order paramagnetic-ferromagnetic transition enlarge the phase transition range. Image 1 • Gd 36 Tb 20 Co 20 Al 24 metallic glass microwires were prepared by melt-extracted method. • The microwires show the maximum magnetic entropy change of 12.36 J. kg−1K−1. • The microwires exhibit refrigerant capacity of 731 J. kg−1. [ABSTRACT FROM AUTHOR]