Construction of dual heterogeneous interface between zigzag-like Mo–MXene nanofibers and small CoNi@NC nanoparticles for electromagnetic wave absorption

Two-dimensional(2D)transition metal carbides(MXene)possess attractive conductivity and abundant surface functional groups,providing immense potential in the field of electromagnetic wave(EMW)absorption.However,high conductivity and spontaneous aggregation of MXene suffer from limited EMW response.Inspired by dielectric–magnetic synergy effect,the strategy of decorating MXene with magnetic elements is expected to solve this challenge.In this work,zigzag-like Mo_(2)TiC_(2)–MXene nanofibers(Mo-based MXene(Mo–MXene)NFs)with cross-linked networks are fabricated by hydrofluoric acid(HF)etching and potassium hydroxide(KOH)shearing processes.Subsequently,Co-metal–organic framework(MOF)and derived CoNi layered double hydroxide(LDH)ultrathin nanosheets are grown inside Mo–MXene NFs,and the N-doped carbon matrix anchored by CoNi alloy nanoparticles formed by pyrolysis is firmly embedded in the Mo–MXene NFs network.Benefiting from synergistic effect of highly dispersed small CoNi alloy nanoparticles,a three-dimensional(3D)conductive network assembled by zigzag-like Mo–MXene NFs,numerous N-doped hollow carbon vesicles,and abundant dual heterogeneous interface,the designed Mo–MXene/CoNi–NC heterostructure provides robust EMW absorption ability with a reflection loss(RL)value of−68.45 dB at the thickness(d)of 4.38 mm.The robust EMW absorption performance can be attributed to excellent dielectric loss,magnetic loss,impedance matching(Z),and multiple scattering and reflection triggered by the unique 3D network structure.This work puts up great potential in developing advanced MXene-based EMW absorption devices.

Wire-feed laser additive manufacturing of dissimilar metals via dual molten pool interface interlocking mechanism

Intermetallic compounds produced in laser additive manufacturing are the main factors restricting the joint performance of dissimilar metals.To solve this problem,a dual molten pool interface interlocking mechanism was proposed in this study.Based on a dual molten pool interface interlocking mechanism,the dissimilar metals,aluminum alloy and stainless steel,were produced as single-layer and multilayer samples,using the wire-feed laser additive manufacturing directed energy deposition technology.The preferred parameters for the dual molten pool interface interlocking mechanism process of the dissimilar metals,aluminum alloy and stainless steel,were obtained.The matching relationship between the interface connection of dissimilar metals and the process parameters was established.The results demonstrated excellent mechanical occlusion at the connection interface and no apparent intermetallic compound layer.Good feature size and high microhardness were observed under a laser power of 660 W,a wire feeding speed of 55 mm/s,and a platform moving speed of 10 mm/s.Molecular dynamics simulations demonstrated a faster rate of aluminum diffusion in the aluminum alloy substrate to stainless steel under the action of the initial contact force than without the initial contact force.Thus,the dual molten pool interface interlocking mechanism can effectively reduce the intermetallic compound layer when dissimilar metals are connected in the aerospace field.

平面激波冲击双层重/轻界面的不稳定性研究

采用可压缩多组分流动高精度求解器数值研究平面激波冲击SF_(6)/Ar/He双层界面(SF_(6)/Ar界面有正弦扰动,Ar/He界面无扰动)的不稳定性问题,重点考察激波强度和界面间距对不稳定性发展的影响.结果表明,在入射激波冲击后第一道界面振幅会逐渐减小到零(反相),随后在相反的方向上持续增长.从第二道界面上反射回来的稀疏波促进或抑制第一道界面的扰动发展,这取决于界面间距D.具体地说,如果D很小,稀疏波在到达第一道界面时界面还没有完成反相,那么会促进第一道界面的扰动发展;如果D很大,稀疏波到达时第一道界面已完成反相,那么会抑制第一道界面的扰动发展.对于任意初始条件,存在一个临界距离,在此距离下稀疏波作用第一道界面时界面刚好完成反相.本文提出了计算这一临界距离的理论模型,为调控第一道界面的扰动增长速率提供了理论支撑.第二道界面的失稳是由扰动透射激波冲击无扰动界面引起的,属于非标准Richtmyer-Meshkov(RM)不稳定性问题,其扰动增长速率强依赖于冲击界面时扰动激波的相位.本文发现Ishizaki模型由于忽略斜压涡量的影响,不能准确预测第二道界面上的扰动增长.综合考虑斜压涡量、速度扰动和压力扰动的影响,本文提出了一个修正的非标准RM不稳定性理论模型,可以对第二道界面的扰动发展给予有效预测.