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The microstructure and magnetic properties including magnetocaloric performance of as-prepared and heat-treated La(Fe,Ni) 11.5 Si 1.5 alloys were systematically investigated. The experimental results indicate that the as-prepared La(Fe,Ni) 11.5 Si 1.5 alloys are composed of α-Fe phase and LaFeSi phase, and the saturation magnetization M s can achieve 159.1 emu/g, as for the larger content of ferromagnetic α-Fe phase. The peritectic reaction occurs during vacuum annealing process, and the decrease of α-Fe phase content reduced the hysteresis loss, meanwhile the NaZn 13 -type structure (1:13 phase) generated. In particular, the magnetocaloric properties of La(Fe,Ni) 11.5 Si 1.5 alloys annealed at 1373 K are superior to that of annealed at 1323 K. And the magnetic entropy change (-Δ S m) of the alloys annealed at 1373 K is up to 20.87 J kg−1 K−1, while Refrigeration Capacity (RC) reaches 415.59 J kg−1 at a magnetic field of 5 T. From the perspective of solid-phase reaction dynamics, the increase of annealing temperature could beneficially accelerate the peritectic reaction process, and result in the increasing content of 1:13 phase, thereby enhancing their magnetocaloric characteristics. Therefore, the microstructure and magnetocaloric properties of La(Fe,Ni) 11.5 Si 1.5 alloys could be effectively modulated by optimizing the annealing process, and it also provides a significant technical reference for the practical application of room-temperature Magnetic Refrigeration (MR) technology. Magnetocaloric properties of La(Fe,Ni) 11.5 Si 1.5 alloys based on NaZn 13 -type structure are distinctly enhanced by modulation of vacuum annealing treatment and Ni-doping. Image 1 • Effects of impurity phases on the magnetic properties were studied in detail. • The saturation magnetization and hysteresis loss of as-prepared alloy are larger than them of heat-treated alloy. • The formation of La(Fe,Ni,Si) 13 (1:13) phase in the alloy is promoted by annealed at higher temperature. • Magnetocaloric properties of La(Fe,Ni) 11.5 Si 1.5 alloy can be effectively improved by rising annealing temperature. [ABSTRACT FROM AUTHOR]

• The solidification process under different mold temperatures was studied. • The duration of the supercooled liquid state was significantly improved as the mold temperature increased. • Increasing the mold temperature improved the solidification time without altering the amorphous solidification behavior. To explore the relationship between mold temperature and the formation of large-size metallic glasses, the influence of mold temperature on the solidification process and microstructure evolution of amorphous melts was investigated. It was found that increasing the mold temperature to 623 K contributes to improving the solidification time from ∼1.79 s to ∼2.32 s without affecting the solidification behavior of amorphous melt. However, the duration of the supercooled liquid state was prolonged by the excessively high mold temperature, resulting in a considerable increase in the glass transition time from ∼12.78 s to ∼145.7 s and a decline in the cooling rate from 27.6 K/s to 2.1 K/s, which ultimately leads to the crystallization of the sample. In addition, it has been observed that the 573 K mold temperature is not only the optimal mold temperature to ensure the amorphous nature of the sample but is also beneficial to improve the internal temperature gradient of the sample, thereby reducing the risk of deformation or cracking. Appropriate control of mold temperature can provide valuable guidance for large-size amorphous castings and associated process parameters. [ABSTRACT FROM AUTHOR]

Induction skull melting (ISM) technology could melt metals with avoiding contamination from crucible. A long-standing problem of ISM is that the low charge energy utilization and inhomogeneous fields have obstructed its application in many critical metal materials and manufacturing processes. The present work investigated the problem through the structure optimization strategy and established a numerical electromagnetic-field model to evaluate components' eddy current loss. Based on the model, the effect of crucible and inductor structure on charge energy utilization, etc. was studied. Furtherly, the charge energy utilization was increased from 27.1 to 45.89% by adjusting the system structure. Moreover, structure modifications are proposed for enhancing electromagnetic intensity and uniformity, charge soft contact and uniform heating. The work constructed a basis for framing new solutions to the problem through ISM device structure optimization. [ABSTRACT FROM AUTHOR]

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]

Herein, the effect of Ni-doping amount on microstructure, magnetic and mechanical properties of Fe-based metallic microwires was systematically investigated further to reveal the influence mechanism of Ni-doping on the microstructure and properties of metallic microwires. Experimental results indicate that the rotated-dipping Fe-based microwires structure is an amorphous and nanocrystalline biphasic structure; the wire surface is smooth, uniform and continuous, without obvious macro- and micro-defects that have favorable thermal stability; and moreover, the degree of wire structure order increases with an increase in Ni-doping amount. Meanwhile, FeSiBNi2 microwires possess the better softly magnetic properties than the other wires with different Ni-doping, and their main magnetic performance indexes of Ms, Mr, Hc and μm are 174.06 emu/g, 10.82 emu/g, 33.08 Oe and 0.43, respectively. Appropriate Ni-doping amount can effectively improve the tensile strength of Fe-based microwires, and the tensile strength of FeSiBNi3 microwires is the largest of all, reaching 2518 MPa. Weibull statistical analysis also indicates that the fracture reliability of FeSiBNi2 microwires is much better and its fracture threshold value σu is 1488 MPa. However, Fe-based microwires on macroscopic exhibit the brittle fracture feature, and the angle of sideview fracture θ decreases as Ni-doping amount increases, which also reveals the certain plasticity due to a certain amount of nanocrystalline in the microwires structure, also including a huge amount of shear bands in the sideview fracture and a few molten drops in the cross-section fracture. Therefore, Ni-doped Fe-based metallic microwires can be used as the functional integrated materials in practical engineering application as for their unique magnetic and mechanical performances. [ABSTRACT FROM AUTHOR]

Herein, the influence of annealing current intensities on magnetic properties of Gd-based microfibers was systematically investigated. The experimental results indicated that the as-prepared microfibers have amorphous structure and excellent thermal-stability, and the Curie temperature T C of which slightly change before and after annealing. The general magnetic physical magnitudes (M s , M r , μ 0 H c and μ m) of microfibers increase firstly and then decrease with the rising of annealing current intensities, and those of the microfibers annealed at 90 mA microfibers are more obvious (M s = 255 A m2/kg and μ m = 0.38 ± 0.01). Similarly, the magnetocaloric parameters of microfibers also increase firstly and then decrease with the rising of current intensities. At 5 T of magnetic field change μ 0 Δ H , the maximum magnetic entropy change Δ S m max and refrigerant capacity RC of 90 mA annealed metallic microfibers are 12.77 J/(kg·K) and 906 J/kg, respectively, and which remarkably increased in compared with the as-prepared state, respectively. From the microstructural evolution perspective, a certain intensity current annealing induces the tendency of micro-regional clusters and nanocrystals, forming atomic ordered regions, and the internal residual stress release with a reduction of magnetic anisotropy. Meanwhile, the magnetic ordering and the critical magnetic-moment rotational driving-force were changed after Fe-doping, resulting in effective improvement of refrigerant capacity. Accordingly, the current-annealed Gd-Al-Co-Fe microfibers can be adopted as low-temperature magnetic refrigeration working-medium, which also provides a theoretical foundation for magnetic refrigeration technology application. Magnetocaloric properties of Gd-Al-Co-Fe metallic microfibers current-annealed at 90 mA are significantly improved according to the microstructural evolution and magnetic ordering modulation. Image 1 • Effects of current annealing intensities on the magnetic properties were investigated in detail. • MCE characteristics of Gd-Al-Co-Fe microfibers could be obviously improved at 90 mA. • Magnetocaloric mechanism is illustrated by the perspective of structural evolution and magnetic ordering transformation. [ABSTRACT FROM AUTHOR]

The effects of trace Fe-doping on the magnetic and magnetocaloric performances of Gd-based metallic microfibers were systematically and detailedly investigated in this article. Experimental results indicated that the Gd-based microfibers prepared by the rotated-dipping process are uniform and continuous, with typically amorphous structure characteristics and favorable thermal stability. Curie temperature T C of Gd-based amorphous microfibers increases with the rising of Fe content, and the T C of GdAlCoFe3 microfibers is the highest at 128.7 K (relatively increased by 15.3 K than before doping). Among the general magnetic performance indicators, the saturation magnetization M s of GdAlCoFe2 microfibers reaches a peak at 264.04 emu/g. Furthermore, the values of magnetocaloric performance indexes of Gd-based amorphous microfibers increase firstly and then decrease with the rising of Fe-doping amount. When the external magnetic field H ex = 50,000 Oe, the maximum magnetic entropy change -Δ S m max, refrigeration capacity RC and relative cooling power RCP of GdAlCoFe1 microfibers are 10.33 J/kg·K, 748.22 J/kg and 1006.90 J/kg, which increased by 0.07 times, 0.13 times and 0.16 times, respectively than before Fe-doping (namely -Δ S m max = 9.68 J/kg·K, RC = 663.79 J/kg, RCP = 871.73 J/kg). From the perspective of microstructural changes, Fe-doping results in the formation tendency of atomic clusters and nanocrystals in micro-regions, the orderly orientation of atoms appears, and the magnetic anisotropy increases accordingly. In addition, the 3d electron layer of the doped Fe element in Gd-Al-Co-Fe quaternary alloy system enhances the RKKY indirectly exchange coupling interaction and changes the state of magnetic entropy, which in turn leads to an increase in Curie temperature and an improvement in magnetocaloric performance. Since RC and RCP are the main indicators in engineering applications, the GdAlCoFe1 amorphous microfibers can be selected as a low-temperature magnetic refrigeration working medium to provide technical guarantee for the application of magnetic refrigeration technology. In comparison to Fe-doped Gd-based amorphous microfibers, # GdAlCoFe1 microfibers have enhanced magnetocaloric properties by coactions of atomic arrangement ordering transformation (AAOT) and magnetic moment ordering transformation (MMOT). Image 1 • Influence of Fe-doping amounts on the magnetocaloric properties was investigated systematically. • MCE properties of # GdAlCoFe1 amorphous fibers were enhanced effectively. • Interaction mechanism was illustrated from the perspective of atomic arrangement and magnetic moment ordering transformation. [ABSTRACT FROM AUTHOR]