Dawei Xing

Binary eutectic clusters and glass formation in ideal glass-forming liquids

In this letter, a physical concept of binary eutectic clusters in “ideal” glass-forming liquids is proposed based on the characteristics of most well-known bulk metallic glasses (BMGs). The authors approach also includes the treatment of binary eutectic clusters as basic units, which leads to the development of a simple but reliable method for designing BMGs more efficiently and effectively in these unique glass-forming liquids. As an example, bulk glass formers with superior glass-forming ability in the Zr–Ni–Cu–Al and Zr–Fe–Cu–Al systems were identified with the use of the strategy.

Crystallization behavior of ZrAlNiCu bulk metallic glass with wide supercooled liquid region

Abstract The crystallization processes of Zr55Al10Ni5Cu30 (at.%) bulk metallic glass from the amorphous state and supercooled liquid region during the continuous heating and isothermal annealing courses were investigated. The apparent activation energy derived from the Kissinger plots for glass transition Eg is higher than that for crystallization Ep and Ex calculated by the peak temperature Tp and onset crystallization temperature Tx during the continuous heating process. The isothermal activation energy obtained using Arrhenius equation shows that it increases accompanying the proceeding of the crystallization transformation. The incubation time of crystallization becomes longer and the crystallization process becomes slower as the annealing temperature is reducing during the isothermal process. The crystallization mechanism was studied using Kolmogorov–Johnson–Mehl–Avrami (KJMA) equation. The results indicate that the Avrami exponent n≈2 at the initial crystallization stage, and it alters gradually following the increasing crystallization volume fraction.

Combined current-modulation annealing induced enhancement of giant magnetoimpedance effect of Co-rich amorphous microwires

We report on a combined current-modulation annealing (CCMA) method, which integrates the optimized pulsed current (PC) and DC annealing techniques, for improving the giant magnetoimpedance (GMI) effect and its field sensitivity of Co-rich amorphous microwires. Relative to an as-prepared Co68.2Fe4.3B15Si12.5 wire, CCMA is shown to remarkably improve the GMI response of the wire. At 10 MHz, the maximum GMI ratio and its field sensitivity of the as-prepared wire were, respectively, increased by 3.5 and 2.28 times when subjected to CCMA. CCMA increased atomic order orientation and circumferential permeability of the wire by the co-action of high-density pulsed magnetic field energy and thermal activation energy at a PC annealing stage, as well as the formation of uniform circular magnetic domains by a stable DC magnetic field at a DC annealing stage. The magnetic moment can overcome eddy-current damping or nail-sticked action in rotational magnetization, giving rise to a double-peak feature and wider working field range (up to ±2 Oe) at relatively higher frequency (f ≥ 1 MHz).

Nanocrystallization of Zr-Ti-Cu-Ni-Be bulk metallic glass

Abstract The nanocrystallization kinetics of Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 (at.%) bulk metallic glass was investigated by differential scanning calorimetry (DSC) in the mode of continuous heating and isothermal annealing. In the case of continuous heating, three exothermic crystallization peaks can be observed, and the peak temperatures display a strong dependence on the heating rates, which can be fitted by a first order decay equation. The activation energies for crystallization are estimated to be E p1 =166.83±8.85 kJ/mol, E p2 =256.15±9.34 kJ/mol, E p3 =174.36±12.56 kJ/mol, which correspond to peak temperatures of T p1 , T p2 , and T p3 , respectively, indicating the formation of different crystallization phases at different stages. In the case of isothermal annealing, the crystallization products under isothermal annealing were observed and determined by transmission electron microscopy (TEM). The precipitation phases of the sample heated at higher temperatures were identified by X-ray diffraction (XRD), showing that the body-centered tetragonal (bct) Zr 2 Cu and hexagonal ZrBe 2 are the primary phases, in spite of the presence of other phases. These results are consistent with the complexity of the DSC curves obtained during the continuous heating and isothermal annealing.

Enhanced refrigerant capacity in Gd-Al-Co microwires with a biphase nanocrystalline/amorphous structure

A class of biphase nanocrystalline/amorphous Gd(50+5x)Al(30−5x)Co20 (x = 0, 1, 2) microwires fabricated directly by melt-extraction is reported. High resolution transmission electron microscopy and Fourier function transform based analysis indicate the presence of a volume fraction (∼20%) of ∼10 nm sized nanocrystallities uniformly embedded in an amorphous matrix. The microwires possess excellent magnetocaloric properties, with large values of the isothermal entropy change (−ΔSM ∼ 9.7 J kg−1 K−1), the adiabatic temperature change (ΔTad ∼ 5.2 K), and the refrigerant capacity (RC ∼ 654 J kg−1) for a field change of 5 T. The addition of Gd significantly alters TC while preserving large values of the ΔSM and RC. The nanocrystallites allow for enhanced RC as well as a broader operating temperature span of a magnetic bed for energy-efficient magnetic refrigeration.

Cryogenic Joule annealing induced large magnetic field response of Co-based microwires for giant magneto-impedance sensor applications

We have presented herein the results of microstructure, surface magnetic domains (SMDs), and giant magneto-impedance (GMI) effect of melt-extracted Co68.15Fe4.35Si12.25B11.25Nb2Cu2 amorphous wires for the first time employed by using a cryogenic Joule annealing (CJA) technique with large DC current amplitude. Compared with the conventional JA method, experimental results indicate that the maximum GMI ratio [ΔZ/Z0]max achieves up to 425% at 8.1 MHz with monotonic increase of the axial magnetic field Hex up to 6.5 Oe for 300 mA (equal to around 1.06 × 106 A/dm−2) CJA-ed wire, which is about 75% larger than the [ΔZ/Z0]max for the 100 mA (nearly 3.53 × 105 A/dm−2) JA-ed microwires. The remarkable features of large and linearly sensitive response field (2.5 ∼ 6.5 Oe) and the sensitivity of 99.4%/Oe with higher GMI ratio simultaneously make the CJA tailored melt-extracted microwires promising candidate materials for miniaturized GMI sensors. Another interesting result of GMI profiles of 200 mA (appropriately eq...

Twin-Detector Sensor of Co-Rich Amorphous Microwires to Overcome GMI Fluctuation Induced by Ambient Temperature

Giant magnetoimpedance (GMI) fluctuation induced by ambient temperature was particularly discussed based on experiments accomplished with melt-extracted Co-rich amorphous microwires. The specimen with Cu electro-plated two-end was placed in a calorstat in magnetically shielded space (MSS), and the impedance stability was measured by means of a precision impedance analyzer in a temperature range of 0°C to 320°C . Experimental results indicated that the critical transition temperature of GMI fluctuation is obtained at 80°C , and even the impedance stability sharply deteriorates with the temperature increasing to 320°C for the increase of resistivity, the intensity of magnetic polarization, and quasi-magnetocrystalline anisotropy energy. Comparison with conventional single-detector sensor (SDS), a novel design mode of twin-detector sensor (TDS) by the differential method at the working temperature of 0°C-80 °C, was presented for effectively overcoming GMI fluctuation to achieve the relatively high-precision measurement of weak magnetic field. It therefore is expected that TDS is favorable for optimizing the systematic structure design of a high-resolution magnetic sensor.

Formation and mechanical properties of bulk Cu-Ti-Zr-Ni metallic glasses with high glass forming ability

Abstract Bulk amorphous Cu 52.5 Ti 30 Zr 11.5 Ni 6 and Cu 53.1 Ti 31.4 Zr 9.5 Ni 6 alloys with a high glass forming ability can be quenched into single amorphous rods with a diameter of 5 mm, and exhibit a high fracture strength of 2 212 MPa and 2 184 MPa under compressive condition, respectively. The stress – strain curves show nearly 2% elastic strain limit, yet display no appreciable macroscopic plastic deformation prior to the catastrophic fracture due to highly localized shear bands. The present work shows clearly evidence of molten droplets besides well-developed vein patterns typical of bulk metallic glasses on the fracture surface, suggesting that localized melting induced by adiabatic heating may occur during the final failure event.

Relating surface roughness and magnetic domain structure to giant magneto-impedance of Co-rich melt-extracted microwires

Understanding the relationship between the surface conditions and giant magneto-impedance (GMI) in Co-rich melt-extracted microwires is key to optimizing their magnetic responses for magnetic sensor applications. The surface magnetic domain structure (SMDS) parameters of ~45 μm diameter Co69.25Fe4.25Si13B13.5-xZrx (x = 0, 1, 2, 3) microwires, including the magnetic domain period (d) and surface roughness (Rq) as extracted from the magnetic force microscopy (MFM) images, have been correlated with GMI in the range 1–1000 MHz. It was found that substitution of B with 1 at. % Zr increased d of the base alloy from 729 to 740 nm while retaining Rq from ~1 nm to ~3 nm. A tremendous impact on the GMI ratio was found, increasing the ratio from ~360% to ~490% at an operating frequency of 40 MHz. Further substitution with Zr decreased the high frequency GMI ratio, which can be understood by the significant increase in surface roughness evident by force microscopy. This study demonstrates the application of the domain period and surface roughness found by force microscopy to the interpretation of the GMI in Co-rich microwires.

Liquid-solid joining of bulk metallic glasses

Here, we successfully welded two bulk metallic glass (BMG) materials, Zr51Ti5Ni10Cu25Al9 and Zr50.7Cu28Ni9Al12.3 (at. %), using a liquid-solid joining process. An atomic-scale metallurgical bonding between two BMGs can be achieved. The interface has a transition layer of ~50 μm thick. The liquid-solid joining of BMGs can shed more insights on overcoming their size limitation resulting from their limited glass-forming ability and then promoting their applications in structural components.