| Electromagnetic interference(EMI)or electromagnetic radiation created by commercial and military electronic devices has led to significant concerns regarding electromagnetic pollution.Searching for EMI shielding materials with light weight,flexibility,good thermal stability,high strength,corrosion resistance,and that are easy to fabricate has become a hot research area.Traditional metals and metal-based composites are the most common materials used to screen electromagnetic waves(EMWs).Metals,like copper,aluminum,and silver,primarily account for high-frequency EMI shielding due to their superhigh electrical conductivity and glorious anticorrosion performance.Whereas,static or tardily varying magnetic fields are generally screened by high magnetic permeability metals,including pure iron,silicon steel,Fe-Al alloy,and permalloy.Yet,the high density,poor flexibility,and restricted tuning in shielding bandwidth of the metals have limited their application primarily to small devices and components.To address these issues,some systematical researches have been conducted in this thesis and the details are summerized as follows:(1)Thin and flexible materials that can provide efficient electromagnetic interference(EMI)shielding are urgently needed,especially if they can be easily processed and withstand harsh environments.Herein,layer-structured Fe-Si-B /Ni-Cu-P metallic glass composites have been developed by simple electroless plating Ni-Cu-P coating on commercial Fe-Si-B metallic glasses.The 0.1 mm-thick composite shows EMI shielding effectiveness of 40 dB over the X-band frequency range,which is higher than those of traditional metals,metal oxides,and their polymer composites of larger thickness.Most of the applied electromagnetic waves are proved to be absorbed rather than bounced back.This performance originates from the combination of a superior soft magnetic property,excellent electrical conductivity,and multiple internal reflections from multilayer composites.In addition,the flexible composites also exhibit good corrosion resistance,high thermal stability,and excellent tensile strength,making them suitable for EMI shielding in harsh chemical or thermal environments.(2)To break the size limitation of metallic glass ribbons,we present a general strategy capable of synthesizing large-sized Fe-based amorphous coatings inlaid with Ni–Cu–P layers (FAC@Ni–Cu–P) via surface modification of Fe-based amorphous powders and high-velocity air fuel technology.The layer structured Fe-based amorphous coatings show high electrical conductivity and good soft magnetic properties,and thus achieve EMI shielding effectiveness of 30 dB.Transmission electron microscopy(TEM)combines off-axis electron holography technique is employed to visualize and analyze the magnetic and electric fields at the inner interface of the coatings.Magnetic induction maps and charge distributions demonstrate that the Ni–Cu–P layers can make strong electromagnetic coupling interaction with the Fe-based amorphous matrix,leading to multiple internal reflection and electromagnetic absorption network.Surface modification of feedstock provides an alternative method for manufacturing Fe-based metallic glasses with high EMI shielding performance.(3)The lack of oxidation resistance of Fe-based amorphous powders(FAP)during hot spray is hindering the progress of soft magnetic coatings towards adoption in military shelter.However,it was confirmed that the resistance to oxidation could be improved by coating Fe-based amorphous powders with Ni–Cu–P shells(FAP@ Ni–Cu–P).Thus,it is essential to investigate the thermal response and gain a fundamental understanding of the anti-oxidation mechanism of the Ni–Cu–P coated powders.Here,we report the structural and chemical evolution of FAP and FAP@ Ni–Cu–P in the presence of air as they are heated to high temperatures.The powders are analysed using in situ X-ray diffraction,to monitor changes in structure and chemical composition.By coupling results from back scattered electron microscopy,we identify mechanisms for morphological and elemental changes,such as oxygen,iron and copper migration during in situ,which demonstrate that the Ni–Cu–P shells deposited on the FAP effectively inhibit the mutual diffusion of Fe and O elements,and are responsible for the anti-oxidation.The ex situ observation provides evidence that the Ni,Cu and P elements of the Ni–Cu–P shell in the thermal treatment under air atmosphere that leads to the formation of a multilayered structure comprised of Ni oxides,Cu oxides,and a small amount of Fe oxides.Cu diffusivity is found to be one-dimensional,Cu elements diffuse from the inner to the outward of Ni–Cu–P shell,forming Cu2O on the outmost of the oxide scale.This result may open new perspectives towards synthesizing Fe-based amorphous powders with improved oxidation resistance. |
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