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Special Issue "Amorphous and Nanocrystalline Materials: Characterizations, Technologies and Applications"

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Dear Colleagues,

Amorphous and nanocrystalline materials have a unique microstructure: long-range atomic disorder and short-range order. Hence, they are thermodynamically metastable. Amorphous materials are often formed in special conditions and have special functional properties, such high elastic moduli and strength, high magnetization, low coercivity, and high catalytic ability. Nanocrystalline materials are closely related to amorphous materials in terms of processing and service conditions. Their characterization, technologies, and applications have long been of interest to metallurgists, physicists, chemists, materials scientists, and engineers.

Prof. Dr. Weimin Wang
Guest Editor

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Keywords

metallic glasses
nanocrystalline materials
microstructure
magnetization
pollution degradation
mechanical properties
rapid solidification
materials computation

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Research

14 pages, 4935 KiB

Open AccessArticle

Centrifugal Atomization of Glass-Forming Alloy Al₈₆Ni₈Y_4.5La_1.5

Jordi Pijuan

Sasha Alejandra Cegarra

Sergi Dosta

Vicente Albaladejo-Fuentes

and

María Dolores Riera

Materials 2022, 15(22), 8159; https://doi.org/10.3390/ma15228159 - 17 Nov 2022

Cited by 3 | Viewed by 1188

Abstract

Centrifugal atomization is a rapid solidification technique for producing metal powders. However, its wide application has been limited to the production of common metal powders and their corresponding alloys. Therefore, there is a lack of research on the production of novel materials such as metallic glasses using this technology. In this paper, aluminum-based glassy powders (Al₈₆Ni₈Y_4.5La_1.5) were produced by centrifugal atomization. The effects of disk speed, atomization gas, and particle size on the cooling rate and the final microstructure of the resulting powder were investigated. The powders were characterized using SEM and XRD, and the amorphous fractions of the atomized powder samples were quantified through DSC analysis. A theoretical model was developed to evaluate the thermal evolution of the atomized droplets and to calculate their cooling rate. The average cooling rate experienced by the centrifugally atomized powder was calculated to be approximately 7 × 10⁵ Ks⁻¹ for particle sizes of 32.5 μm atomized at 40,000 rpm in a helium atmosphere. Amorphous fractions from 60% to 70% were obtained in particles with sizes of up to 125 μm in the most favorable atomization conditions. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Materials: Characterizations, Technologies and Applications)

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16 pages, 11667 KiB

Open AccessArticle

Fe-Based Amorphous Magnetic Powder Cores with Low Core Loss Fabricated by Novel Gas–Water Combined Atomization Powders

and

Materials 2022, 15(18), 6296; https://doi.org/10.3390/ma15186296 - 10 Sep 2022

Cited by 10 | Viewed by 1454

Abstract

FeSiBCCr amorphous powders were produced by a novel gas–water combined atomization process, and the corresponding MPCs (magnetic powder cores) were subsequently fabricated by phosphating treatment (0.4~1.6 wt.%), cold pressing (550~2350 MPa), and annealing (423~773 K), respectively. The results showed that the powders had high circularity, excellent thermal stability (ΔT = 59 K), and high saturation magnetization (0.83 T), which could provide raw powders for high-performance MPCs. With increasing phosphoric acid concentrations, despite the increase in DC-bias%, the uniformity of the insulation layers deteriorated, which led to a decrease in permeability and an increase in core loss. With increasing compaction pressures, the core loss increased continuously, and the permeability and DC-bias% first increased and then decreased. When annealing below the crystallization temperature, with increasing annealing temperatures, the permeability increased, and the core loss and DC-bias% decreased continuously. Under the optimized process of 0.4 wt.% phosphating concentration, 550 MPa pressure, and 773 K annealing temperature, the MPCs had a permeability of 21.54 ± 1.21, DC-bias% of 90.3 ± 0.2, and a core loss (B_m = 50 mT, f = 100 kHz) of 103.0 ± 26.3 mW cm⁻³. The MPCs had excellent high-frequency low-loss characteristics and showed great application potential under the development trends of high current, high power, and high frequency of electronic components. Full article

(This article belongs to the Special Issue Amorphous and Nanocrystalline Materials: Characterizations, Technologies and Applications)

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Special Issue "Amorphous and Nanocrystalline Materials: Characterizations, Technologies and Applications"

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