Search

A seven-component (FeCo) x BSiVCuY amorphous/nanocrystalline alloy system with high ferromagnetic element contents (x = 85, 86 and 87, at atomic percent) was synthesized by rapid quenching method. The microstructure, crystal structure, magnetic property and crystallization behavior were systematically investigated. It is found that the highest saturation magnetization of these as-cast ribbons reaches 1.80 T. Upon heating, two different crystal precipitated phases bcc-Fe (Co) and Fe-metalloids appear successively with temperature intervals (Δ T x) as large as 193 K. Comparing with typical Fe-based amorphous/nanocrystallization alloys, (Fe 0.8 Co 0.2) 87 B 10 Si 1 V 0.5 Cu 0.5 Y 1 alloy shows an ultra-low primary crystallization activation energy and a large secondary crystallization activation energy, indicating an extremely large annealing temperature window more than 200 K beneficial for their processing. Therefore, this series of amorphous alloys provide potential precursors with decreasing annealing temperature and time for producing ferromagnetic nanocrystalline alloys, which can significantly reduce the cost for industrial production. • Ultra-high ferromagnetic element content of 87 atomic% was achieved in (FeCo) x BSiVCuY amorphous/nanocrystalline alloys. • The highest saturation magnetization of these as-cast ribbons can reach 1.80 T. • Significant different crystallization activation energies exist in the primary and secondary exothermic peaks. • A large annealing temperature window about 200 K facilitates to obtain dual-phase with improved magnetic properties. [ABSTRACT FROM AUTHOR]

The range of supercooled liquid region (Δ T) is the key parameter for evaluating the thermal stability and glass-forming ability of metallic glasses. The enhancement of Δ T is of significance not only for the glass formation and stability, but also for their thermoplastic forming ability. Traditional approaches to increase Δ T are composition regulation or dynamical modulation, which are either time-consuming or difficult to be controlled. Here, through a high-frequency ultrasonic vibration treatment, we show that the Δ T of a La-based metallic glass can be significantly widened from 64 K to 83 K, around 30% increment. This behavior is physically originated from the denser atomic packing and a lower stable basin in the energy landscape induced by the ultrasonic vibration energy. This work might provide a ready route to stabilize the supercooled liquid and glass, and give an insight into the understanding of the glass-forming of amorphous materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Metallic glasses have many intrinsic and universal dynamic relaxations observed below the glass-transition temperature. However, these relaxations have mostly been studied on heating and seldom investigated on cooling. In the present work, the slow β and fast β′ relaxations of La 60 Ni 15 Al 25 metallic glass are studied in sequential heating and cooling experiments under continuous mechanical vibration using a dynamic mechanical analyzer. A slow β relaxation peak is observed on cooling, and compared with the preceding heating step, its peak temperature, activation energy and characteristic relaxation time are all shifted to lower values. On the contrary, a fast β′ relaxation peak is always present on heating, but undetectable on consequent cooling. Only when the metallic glass is cooled below a critical temperature, a certain value of supercooling is achieved, then the fast β′ relaxation is found during subsequent reheating. The work introduces a new approach to investigate dynamic relaxations in metallic glasses and discusses a new possibility of the origin of the fast β' relaxation. • Relaxations of metallic glasses are studied on cooling instead of on heating. • On cooling, the slow β relaxation exhibits lower peak temperature. • On cooling, the fast β′ relaxation cannot be detected. • A supercooling is required to see the fast β′ relaxation on heating. [ABSTRACT FROM AUTHOR]

We have carried out a systematic investigation of the structure and magnetism of Fe 75-x Cr 25 Ga x (11 < x < 33) and Fe 50 Cr 50-y Ga y (0 < y < 33) series of compounds. The results show that the parent Fe 50 Cr 25 Ga 25 phase has a higher tolerance for Ga replacing Cr than replacing Fe atoms. An abrupt decrease of the Curie temperature and magnetization was observed at the composition of Fe 50 Cr 25 Ga 25. This can be explained by anti-site occupation and transition of magnetic structure in these series. The induced structure is energetically favorable according to first-principles calculations. This work clarifies our understanding of the interdependence between the atomic configurations and magnetism in Fe-based Heusler compounds, and provides a method to deduce the atomic configurations through the evolution of magnetism. • An abrupt decrease of Curie temperature and magnetization was observed in the Fe 50 Cr 50-y Ga y series. • An anti-site atom occupation and transition of magnetic structure are proposed for the observed phenomenon. • Deducing the atomic configurations based on the magnetic behaviors is proved to be valid. [ABSTRACT FROM AUTHOR]

Rejuvenation of metallic glasses (MGs), as to store more energy into the disordered system, can be achieved by many methods. Introducing hydrogen into MG is expected to be an efficient method to induce rejuvenation, yet it appears strange that arc-molten MGs with hydrogen have increased plasticity whereas electrically charged MG doesn't. In this work, we report that by leaving MGs in an alkaline environment, a predominant rejuvenation effect can be achieved, with both tensile ductility and compressive plasticity enhanced yet no deteriorate corrosion effects made. The enthalpy of the MG is increased from 0.95 to 1.77 kJ/mol and the energy conversion efficiency is increased as high as 86% at the optimal conditions. Although the method mainly rejuvenates the 10 μm-thick surface layers, the whole sample gets distinctly improved mechanical performance after the treatments, including enhanced high-temperature ductility and room-temperature plasticity. This method enlightens us that a control of the product and pace of the chemical reaction can rejuvenate MG, and provides a new fabrication approach for the MGs to achieve better mechanical performance. • Chemical immersion method is applied to achieve predominant rejuvenation of metallic glasses. • The mechanical properties including tension/compression plasticity are greatly improved by the present chemical strategy. • The energy-conversion efficiency is as high as 86%. [ABSTRACT FROM AUTHOR]

Structural heterogeneity of metallic glass is critical in cryogenic rejuvenation but chemical heterogeneity is seldom explored. Here we show that cryogenic rejuvenation of a nominal La 60 Al 25 Ni 15 (at.%) metallic glass can be enabled with little impurities of Ce and Fe inside the material. Besides, these impurities can significantly enlarge the plastic strain conveyed by the material in bending. In addition, the heterogeneous structure is observed in the sample containing these chemical heterogeneities. Although the glass forming ability of the metallic glass is worsened, our study highlights the impact of chemical heterogeneity on the cryogenic rejuvenation of metallic glasses. Image 1 • The importance of chemical heterogeneity on cryogenic rejuvenation of metallic glasses. • A little impurity can enable energy-increase in La 60 Al 25 Ni 15 (at.%) metallic glass. • Plasticity-enhancement of rejuvenated glass. [ABSTRACT FROM AUTHOR]

Abstract: The thermal stability and the spin transportation phenomenon at room temperature and 140 °C of a series of magnetic tunneling junctions with the structure of bottom electrode/PtMn/Pinned layer/ AlO x /CoFe/NiFe/top electrode have been investigated. The MR ratio decreases from 33.5% at room temperature to 29% at 140 °C. The MR ratio at room temperature increases roughly 0.8% after thermal treatment at temperatures above 60 °C. This is related to the thermal relaxation of the strains existing in the samples. [Copyright &y& Elsevier]