Browsing by Author "Zhu, H"

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    Direct measurement of the intrinsic sharpness of magnetic interfaces formed by chemical disorder using a He+ beam
    (American Chemical Society, 2018-04-27) Causer, GL; Cortie, DL; Zhu, H; Ionescu, M; Mankey, GJ; Wang, XL; Klose, F
    Using ion beams to locally modify material properties and subsequently drive magnetic phase transitions is rapidly gaining momentum as the technique of choice for the fabrication of magnetic nanoelements. This is because the method provides the capability to engineer in three dimensions on the nanometer length scale. This will be an important consideration for several emerging magnetic technologies (e.g., spintronic devices and racetrack and random-access memories) where device functionality will hinge on the spatial definition of the incorporated magnetic nanoelements. In this work, the fundamental sharpness of a magnetic interface formed by nanomachining FePt3 films using He+ irradiation is investigated. Through careful selection of the irradiating ion energy and fluence, room-temperature ferromagnetism is locally induced into a fractional volume of a paramagnetic (PM) FePt3 film by modifying the chemical order parameter. A combination of transmission electron microscopy, magnetometry, and polarized neutron reflectometry measurements demonstrates that the interface over which the PM-to-ferromagnetic modulation occurs in this model system is confined to a few atomic monolayers only, while the structural boundary transition is less well-defined. Using complementary density functional theory, the mechanism for the ion-beam-induced magnetic transition is elucidated and shown to be caused by an intermixing of Fe and Pt atoms in antisite defects above a threshold density. © 2018 American Chemical Society.
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    Effects of heat treatment on microstructure and mechanical properties of wire arc additively manufactured Hastelloy C276 alloy
    (Materials Australian and The Australian Ceramic Society, 2022-06-01) Qiu, Z; Wu, B; Zhu, H; Wang, ZY; Wexler, D; Van Duin, S; Pan, Z; Li, H
    Hastelloy C276 is a Ni-Cr-Mo based superalloy which has a high potential for application in high temperature and extreme corrosive environment due to its high corrosion resistance and excellent mechanical properties. In this research, the wire arc additive manufacturing (WAAM) process was successfully used to fabricate the defect-free Hastelloy C276 component. The microstructure of the component was characterized using optical microscopy, scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray diffraction, the mechanical properties were evaluated via tensile and hardness tests. The as-deposited component exhibited anisotropy on both microstructure and mechanical properties. The influences of solid solution heat treatment and stress relief heat treatment on microstructure and mechanical properties were also investigated. It was found that both microstructure and mechanical properties were significantly modified after heat treatment. Preliminary creep tests indicted the texture has a strong influence on the creep performance of the component.
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    Polarized neutron reflectometry of epitaxial Fe[0.25 + x] Pt[0.75 – x] layers.
    (Institute of Electrical and Electronics Engineers (IEEE), 2018-04-27) Mankey, GJ; Causer, GL; Cortie, DL; Wang, X; Zhu, H; Lonescu, M; Klose, F
    Epitaxial Fe[0.25 + x]Pt[0.75 - x] layers can be either antiferromagnetic (AF) or ferromagnetic (FM) depending on the degree of chemical ordering controlled by the deposition temperature. Our neutron diffraction studies were the first to study AF phase transitions in these thin films [1] and we have also shown using PNR that a mixed AF-FM film is exchange biased with itself [2]. In AF-FM exchange-biased superlattices with a modulated chemical order parameter, PNR shows the magnetization can be modulated through the film thickness with no composition modulations [3]. Our recent results reveal that He+ ion bombardment and annealing can be applied toward controlling magnetic phases in epitaxial Fe [0.25] Pt [0.75] layers [4]. © Copyright 2024 IEEE - All rights reserved, including rights for text and data mining and training of artificial intelligence and similar technologies.