Ying Zhu

Chemical sintering of direct-written silver nanowire flexible electrodes under room temperature

Transparent and flexible electrodes on cost effective plastic substrates for wearable electronics have attract great attention recently. Due to the conductivity and flexibility in network form, metal nanowire is regarded as one of the most promising candidates for flexible electrode fabrication. Prior to application, low temperature joining of nanowire processes are required to reduce the resistance of electrodes and simultaneously maintain the dimensionality and uniformity of those nanowires. In the present work, we presented an innovative, robust and cost effective method to minimize the heat effect to plastic substrate and silver nanowires which allows silver nanowire electrodes been directly written on polycarbonate substrate and sintered by different electrolyte solutions at room temperature or near. It has been rigorously demonstrated that the resistance of silver nanowire electrodes has been reduced by 90% after chemical sintering at room temperature due to the joining of silver nanowires at junction areas. After ∼1000 bending cycles, the measured resistance of silver nanowire electrode was stable during both up-bending and down-bending states. The changes of silver nanowires after sintering were characterized using x-ray photoelectron spectroscopy and transmission electron microscopy and a sintering mechanism was proposed and validated. This direct-written silver nanowire electrode with good performance has broad applications in flexible electronics fabrication and packaging.

Microstructure- and Strain Rate-Dependent Tensile Behavior of Fiber Laser-Welded DP980 Steel Joint

DP980 steels were butt-welded by fiber laser welding. The microstructures, microhardness distribution, and tensile behavior of the joint were investigated. The results showed that the fusion zone (FZ) consisted of fully martensite with higher hardness compared to the base metal (BM). A softened zone (20 HV0.2 drop) was produced in heat-affected zone due to martensite tempering during the laser welding. The ultimate tensile strength (UTS) and yield strength (YS) of the laser-welded joint were not degraded compared to BM with the existence of softened zone. The UTS and YS of the welded joint increased with the increase of tensile strain rate. The work hardening exponents of the BM and welded joint showed weak positive strain rate dependence. The deformation of softened zone was restrained by the hardened FZ during loading, resulting in a higher work hardening rate of softened zone than that of BM. The failure of welded joint occurred in the BM instead of softened zone. The fracture surfaces of the joint exhibited typical ductile fracture over strain rate from 0.0001 to 0.1xa0s−1.

The braze joint between Al2O3 to 1Cr18Ni9Ti using a nickel foam

In this paper, a metallic foam interlayer is used to relieve the stresses between the ceramic to metal brazed joint. The brazing of Al2O3 and 1Cr18Ni9Ti stainless steel was accomplished using different thicknesses of Ni foam interlayer. The shear test of the brazing joint was carried out, and the maximum shear strength of 119.86xa0MPa was achieved when using 0.2xa0mm thickness Ni foam as an interlayer. The microstructures and chemical compositions of the joint interfaces were investigated by scanning electron microscopy. It was found that the change of the distribution of element Ti in the interface would restrain the formation of brittle intermetallic compounds when using a Ni foam as the interlayer, which drastically improves the performance of the brazed joint.

Effects of Laser Shock Processing on Fatigue Crack Growth in Ti-17 Titanium Alloy

The effects of laser shock processing (LSP) on the fatigue crack properties of Ti-17 titanium alloy are investigated. Surfaces on either side of a fatigue slot are subjected to LSP. The residual stress of the irradiated surface is measured by x-ray diffraction measurement and fatigue crack growth testing of the treated and untreated specimens. The fatigue fracture morphology and microstructure are examined by scanning electron microscopy and transmission electron microscopy. Proliferation and tangles of dislocations occur in the Ti-17, and the density of dislocation increases after the LSP treatment. The fine spacing of the fatigue striations indicates that LSP produces residual compressive stress on the irradiated surfaces which can delay micro-crack formation and expansion. Consequently, the fatigue propagation life of the specimen increases considerably after LSP.

Improved hydrogen ionization rate in enhanced glow discharge plasma immersion ion implantation by enlarging the interaction path using an insulating tube

A small pointed hollow anode and large tabular cathode are used in enhanced glow discharge plasma immersion ion implantation (EGD-PIII). Electrons are repelled from the substrate by the electric field formed by the negative voltage pulses and concentrate in the vicinity of the anode to enhance the self-glow discharge process. To extend the application of EGD-PIII to plasma gases with low ionization rates, an insulating tube is used to increase the interaction path for electrons and neutrals in order to enhance the discharge near the anode. Results obtained from numerical simulation based on the particle-in-cell code, finite element method, and experiments show that this configuration enhances the ionization rate and subsequent ion implant fluence. The process is especially suitable for gases that have low ionization rates such as hydrogen and helium.

Nanoscale Wire Bonding of Individual Ag Nanowires on Au Substrate at Room Temperature

The controllable wire bonding of individual Ag nanowires onto a Au electrode was achieved at room temperature. The plastic deformation induced by pressure using nanoindentation could break the protective organic shell on the surface of the Ag nanowires and cause atomic contact to promote the diffusion and nanojoining at the Ag and Au interface. Severe slip bands were observed in the Ag nanowires after the deformation. A metallic bond was formed at the interface, with the Ag diffusing into the Au more than the Au diffused into the Ag. This nanoscale wire bonding might present opportunities for nanoscale packaging and nanodevice design.Graphical Abstract

Effects of Laser Shock Processing on Fatigue Performance of Ti-17 Titanium Alloy

Abstract Ti-17 titanium alloy was treated by laser shock processing (LSP) and the high-frequency fatigue properties were evaluated. The fatigue fracture and the microstructures were observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). The result shows that the average fatigue life of the LSP sample increases 2.62 times at maximum stress 300u2006MPa under stress ratio is 0.1. The micro-hardness of the samples subjected to LSP increases 20u2006% compared with the basic material. The proliferation and tangles of dislocations of Ti-17 occurs and the density of dislocation increases after LSP treatment. The high dislocation density of LSP impacts changes the initiation of crack from corner to subsurface, and hinders the crack extension, thus increases the fatigue performance of the Ti-17.

Effects of Laser Shock Processing on Impact Toughness of Ti-17 Titanium Alloy

Abstract Ti-17 titanium alloy was treated with laser shock processing (LSP) and tested for impact toughness. Residual compressive stress, cross-section hardness, microstructure, and the impact toughness properties of the treated alloy samples were evaluated. The average impact toughness of the samples subjected to LSP increased by 10u2006J compared with that of the base material. The samples subjected to LSP remained connected after an impact test, whereas untreated samples completely ruptured. The location of fracture initiation shifted from the center to the side to the Charpy-V notch region because of the stress concentration induced by LSP. The stress concentration was induced by the uneven microhardness of the samples treated with LSP. The hardness of the irradiated surface increased compared with that of the base metal because of the higher dislocation density and smaller grains produced by LSP.

High Strain Rate Response of 7055 Aluminum Alloy Subject to Square-spot Laser Shock Peening

The influences of laser pulse energy and impact time on high strain rate response of 7055 aluminum alloy subject to square-spot laser shock peening (SLSP) were investigate. Microstructural evolution was characterized by OM, SEM and TEM. Microhardness distribution and in-depth residual stress in 15 J with one and two impacts and 25 J with one and two impacts were analyzed. Results show that the original rolling structures were significantly refined due to laser shock induced recrystallization. High density of microdefects was generated, such as dislocation tangles, dislocation wall and stacking faults. Subgrains and nanograins were induced in the surface layer, resulting in grain refinement in the near surface layer after SLSP. Compressive residual stresses with maximum value of more than -200 MPa and affected depths of more than 1 mm can be generated after SLSP. Impact time has more effectiveness than laser pulse energy in increasing the magnitude of residual stress and achieving thicker hardening layer.

Microstructure and Mechanical Properties of C/C Composite/TC17 Joints with Ag-Cu-Ti Brazing Alloy

Carbon/Carbon composite(C/C) was vacuum brazed to titanium alloy (TC17) using Ag-Cu-Ti brazing alloy. The effects of brazing temperature on the interfacial microstructure and joint properties were investigated by energy dispersive spectrometer (EDS), a scanning electron microscope (SEM), X-ray diffraction (XRD) and Gleeble1500D testing machine. Results show that C/C composite and TC17 were successfully brazed using AgCuTi brazing alloy. Various phases including TiC, Ag(s, s), Cu(s, s), Ti3Cu4, TiCu, and Ti2Cu were formed in the brazed joint. The maximum shear strength of the brazed joints with AgCuTi brazing alloy was 24±1 MPa when brazed at 860°C for 15 min.