Pitting corrosion behavior and corrosion protection performance of cold sprayed double layered noble barrier coating on magnesium-based alloy in chloride containing solutions

Nitrogen processed, cold sprayed commercially pure(CP)-Al coatings on Mg-based alloys mostly lack acceptable hardness, wear resistance and most importantly are highly susceptible to localized corrosion in chloride containing solutions. In this research, commercially pure α-Ti top coating having good pitting potential(~1293 mV_(SCE)), high microhardness(HV_(0.025): 263.03) and low wear rate was applied on a CP-Al coated Mg-based alloy using high pressure cold spray technology. Potentiodynamic polarization(PDP) curves indicated that the probability of transition from metastable pits to the stable pits for cold spayed(CS) Al coating is considerably higher compared to that with the CS Ti top coating(for Ti/Al/Mg system). In addition, CS Ti top coating was in the passivation region in most pH ranges even after 48 h immersion in 3.5 wt% NaCl solution. The stored energy in the CS Ti top coating(as a passive metal) was presumed to be responsible for the easy passivation. Immersion tests indicated no obvious pits formation on the intact CS Ti top coating surface and revealed effective corrosion protection performance of the CS double layered noble barrier coatings on Mg alloys in 3.5 wt% NaCl solution even after 264 h.

Additive Manufacturing of Large-scale Metal Mesh with Core-shell Composite Structure for Transparent Electromagnetic Shielding/glass Heater

Transparent electromagnetic(EM)shielding glass with a metal mesh has significant potential for application in different fields of EM radiation and anti-EM interference light-transmitting observation windows.In particular,a transparent EM-shielding glass with a large-aspect-ratio metal mesh can effectively alleviate the contradictory problems of shielding effectiveness and light-transmission performance constraints.However,the fabrication of high-aspect-ratio metal meshes on glass substrates has problems such as high cost,complex processes,low efficiency,small area,and easy damage issues,which limit their application in the field of high-performance,transparent EM-shielding glass.Therefore,this paper proposes a composite additive manufacturing process based on electric-field-driven microjet 3D printing and electroplating.By fabricating metal meshes with an Ag-Cu core-shell structure on a glass substrate,EM-shielding glass with high shielding efficiency and light transmission can be manufactured without increasing the aspect ratio of the metal meshes.The prepared Ag-Cu composite metal mesh has excellent optoelectronic properties(period 250𝜇m,line width 10𝜇m,90.1%transmission at 550 nm visible light,square resistance 0.21Ω/sq),efficient electrothermal effect(3 V DC voltage can reach 189°C steady-state temperature),stable EM-shielding effectiveness(average shielding effectiveness 23 dB at X-band),and acceptable mechanical and environmental stability(less than 3%change in square resistance after 150-times adhesion test and less than 6%and 0.6%change in resistance after 72 h in acid and alkali environments,respectively).This method provides a new solution for the mass production of high-performance large-area transparent electric heating/EM-shielding glass.

Recent advances in nanofiber-based flexible transparent electrodes

Flexible and stretchable transparent electrodes are widely used in smart display,energy,wearable devices and other fields.Due to the limitations of flexibility and stretchability of indium tin oxide electrodes,alternative electrodes have appeared,such as metal films,metal nanowires,and conductive meshes.However,few of the above electrodes can simultaneously have excellent flexibility,stretchability,and optoelectronic properties.Nanofiber(NF),a continuous ultra-long one-dimensional conductive material,is considered to be one of the ideal materials for high-performance transparent electrodes with excellent properties due to its unique structure.This paper summarizes the important research progress of NF flexible transparent electrodes(FTEs)in recent years from the aspects of NF electrode materials,preparation technology and application.First,the unique advantages and limitations of various NF materials are systematically discussed.Then,we summarize the preparation technology of various advanced NF FTEs,and point out the future development trend.We also discuss the application of NFs in solar cells,supercapacitors,electric heating equipments,sensors,etc,and analyze its development potential in flexible electronic equipment,as well as problems that need to be solved.Finally,the challenges and future development trends are proposed in the wide application of NF FTEs in the field of flexible optoelectronics.

激光功率对17-4PH丝材激光熔覆组织及硬度的影响

目的研究激光功率对17-4PH不锈钢丝材激光熔覆组织及硬度的影响,以确定最佳激光熔覆功率,为17-4PH不锈钢丝材激光熔覆的应用提供参考。方法在27SiMn钢活塞杆表面,对17-4PH不锈钢丝材进行了不同激光功率熔覆试验,利用金相显微镜和扫描电子显微镜表征不同激光功率熔覆层的微观组织,使用硬度计测量不同激光功率熔覆层和基体的硬度。结果当激光功率分别为1600、1800、2000、2200 W时,熔覆层的高度由1119μm降低到1006μm,基体的穿透深度和热影响区宽度都随激光功率的增加而增大,熔覆层的组织主要为较短无方向性的板条马氏体。当激光功率为2400、3000 W时,熔覆层的高度、基体的穿透深度和热影响区宽度均随激光功率的增大而增加,最大值分别达到1119、310、638μm,熔覆层的组织主要由具有方向取向的板条马氏体组成,靠近基材的位置由晶粒细小而致密的等轴晶组成,随着激光功率的增加,熔覆层弥散析出的沉淀颗粒越来越多。此外,熔覆层和热影响区的显微硬度均高于基体,随着激光功率的增加,熔覆层的显微硬度明显增大,最高可达479.4HV_(0.2)。结论综合考虑激光功率对17-4PH不锈钢丝材激光熔覆组织及硬度的影响,2600 W为最佳激光熔覆功率。

Emerging Flexible Thermally Conductive Films:Mechanism,Fabrication,Application

Effective thermal management is quite urgent for electronics owing to their ever-growing integration degree,operation frequency and power density,and the main strategy of thermal management is to remove excess energy from electronics to outside by thermal conductive materials.Compared to the conventional thermal management materials,flexible thermally conductive films with high in-plane thermal conductivity,as emerging candidates,have aroused greater interest in the last decade,which show great potential in thermal management applications of next-generation devices.However,a comprehensive review of flexible thermally conductive films is rarely reported.Thus,we review recent advances of both intrinsic polymer films and polymer-based composite films with ultrahigh in-plane thermal conductivity,with deep understandings of heat transfer mechanism,processing methods to enhance thermal conductivity,optimization strategies to reduce interface thermal resistance and their potential applications.Lastly,challenges and opportunities for the future development of flexible thermally conductive films are also discussed.

Influence of laser parameters on segregation of Nb during selective laser melting of Inconel 718

A transient three-dimensional powder-scale model was established for understanding the flow field and mass transfer within the molten pool during the selective laser melting(SLM)of Inconel 718 alloy by considering some important physical phenomena,such as,a transition from powder to solid,nonlinearities produced by temperature-dependent materials’properties,and fluid flow in the calculation.The influence of laser power or scanning speed on the flow field and cooling rate was discussed in detail.The simulation results reveal that the motion of molten pool and higher cooling rate promote the mass transfer and benefit the solute distribution by increasing laser power.However,with increasing the scanning speed,the melt flow speed and cooling rate are elevated,resulting in an agglomeration of the solute elements,which is ascribed to the shorter dwelling time of liquid.Therefore,the segregation of Nb can be effectively suppressed by increasing laser power or decreasing scanning speed,which can decrease the dwelling time of liquid.

Adiabatic shear instability in a titanium alloy:Extreme deformation-induced phase transformation,nanotwinning,and grain refinement

Increasingly harsh service conditions place higher requirements for the high strain-rate performance of titanium alloys.Adiabatic shear band(ASB),a phenomenon prone to dynamic loading,is often accom-panied by catastrophic damage.Yet,it is unclear how the internal nanostructures are related to shear instability.Here we report detailed microstructural evolution in the ASB of a titanium alloy via in-depth focused ion beam(FIB),transmission Kikuchi diffraction(TKD),and high-resolution transmission electron microscope(HRTEM)analyses,with the deformation instability phenomenon discussed from the energy perspective.The ASB interior undergoes multifaceted changes,namely deformation-induced beta-to-alpha transformation and deformation-induced martensitic transformation to form substantially refined and heterogeneous structures.Meanwhile,two types of extremely fine twins are identified to occur within both nano-sized martensite and alpha phase.The critical plastic work representing the onset of adiabatic shear instability and dynamic equilibrium is observed to be constant for a specific structure in the same deformation mode.The energy analysis could be extended to other materials subjected to high strain-rate dynamic deformation.

3D Printing of Continuous Fiber Reinforced Polymer Composites:Development,Application,and Prospective

Continuous fiber reinforced polymer composites(CFRPC)have been widely used in the field of automobile,air-craft,and space due to light weight,high specific strength and modulus in comparison with metal as well as alloys.Innovation on 3D printing of CFRPCs opened a new era for the design and fabrication of complicated composite structure with high performance and low cost.3D printing of CFRPCs provided an enabling technol-ogy to bridge the gaps between advanced materials and innovative structures.State-of-art has been reviewed according to the correlations of materials,structure,process,and performance as well as functions in 3D printing of CFRPCs.Typical applications and future perspective for 3D printing of CFRPCs were illustrated in order to grasp the opportunities and face the challenges,which need much more interdisciplinary researches covering the advanced materials,process and equipment,structural design,and final smart performance.

Microstructure, tensile properties and mechanical anisotropy of selective laser melted 304L stainless steel

The microstructure and mechanical properties of 304 L stainless steel fabricated by selective laser melting are investigated in this study.With the optimized laser processing parameters,a relative density of 99.9%is achieved with fine austenite grains and nanoscale cellular subgrains in size of approximately 0.5μm.The presence ofδ-ferrite andσphase precipitates is identified by the x-ray diffraction and transmission electron microscopy.Moreover,the microstructure is identified as an austenite matrix with about 4%δ-ferrite and a trace amount ofσphase by using electron backscattered diffraction analysis.These smallσphase particles are mainly distributed along austenite grain boundaries.Furthermore,the presence of nanoscale cellular subgrains contributes to the good tensile strength and ductility of the selective laser melted 304 L,along with precipitate strengthening and strain hardening.Tensile property anisotropy is also identified in this 304 L,which is attributed to the microstructure difference on vertical and horizontal planes.