Y. D. Han

Pressure-assisted low-temperature sintering for paper-based writing electronics

With the aim of preparing paper-based writing electronics, a kind of conductive pen was made with nano-silver ink as the conductive component and a rollerball pen as the writing implement. This was used to direct-write conductive patterns on Epson photo paper. In order to decrease the sintering temperature, pressure was introduced to enhance the driving forces for sintering. Compared with hot sintering without pressure, hot-pressure can effectively improve the conductivity of silver coatings, reduce the sintering time and thus improve productivity. Importantly, pressure can achieve a more uniform and denser microstructure, which increases the connection strength of the silver coating. At the optimum hot-pressure condition (sintering temperature 120 ° C/sintering pressure 25 MPa/sintering time 15 min), a typical measured resistivity value was 1.43 × 10⁻⁷ Ω m, nine greater than that of bulk silver. This heat treatment process is compatible with paper and does not cause any damage to the paper substrates. Even after several thousand bending cycles, the resistivity values of writing tracks by hot-pressure sintering stay almost the same (from 1.43 × 10⁻⁷ to 1.57 × 10⁻⁷ Ω m). The stability and flexibility of the writing circuits are good, which demonstrates the promising future of writing electronics.

Fatigue strength improvement of stainless steel using weld toes dressing with low transformation temperature welding wire

Abstract In the present study, low transformation temperature welding wire (LTTW), which can induce residual compressive stress around 304L welded joints, has been developed to improve the fatigue performance of welded joints. Procedure of design and chemical composition of weld metal and deposited metal of LTTW are introduced. The microstructure of weld metal of LTTW is composed of low carbon martensite and residual austenite. The residual stress distribution of a single welding bead of LTTW was measured and the result shows that compressive residual stress is generated. In addition, fatigue test was also carried out on no-load cruciform welded joints of 304L stainless steel under three conditions: as welded, 308L dressing and LTTW dressing. The result shows that the fatigue life of LTTW dressing joints (2×106 cycles) is improved by 14–23 times and 3–6 times compared with that of as welded joints and 308L dressing joints.

Electrochemical Behavior of Corrosion Resistance Alloys

The electrochemical behavior of corrosion resistance alloys (316L SS, 2205 DSS and Inconel 625) was carried out at ambient temperature in 3.5% NaCl solution using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. Some significant characterization parameters such as Ecorr, Eb, Icorr and △E in polarisation curves were analyzed and compared to reveal the corrosion resistance of corrosion resistance alloys. The ZsimpWin software was utilized to discuss the Nyquist plots of various corrosion resistance alloys. The result shows that the corrosion resistance of the corrosion resistance alloys in 3.5% NaCl solution at ambient temperature follows the sequence: Inconel 625> 2205 DSS > 316L SS.

Study on residual stress in socket weld by numerical simulation and experiment

In this paper, welding residual stress in socket weld of 304L stainless steel pipe was investigated using numerical simulation and validated by X-ray stress measurement. From the simulation results, the maximum tensile residual stresses were located at weld root and weld toe on both sides of the weld along pipe, which led to the fatigue failure. Pre-bevelling and low transformation temperature (LTT) dressing could decrease tensile residual stress both in hoop and axial direction at weld root and weld toe. After LTT dressing, compressive residual stress was generated throughout weld toe. Compressive stress can delay fatigue crack initiation and propagation. Therefore, pre-bevelling and LTT dressing can improve the fatigue life of socket weld.

Ageing study of interfacial intermetallic growth in a lead-free solder reinforced with Ni-coated carbon nanotubes

In this study, varying amounts of Ni-CNTs were incorporated into the Sn-Ag-Cu matrix to form the composite solders. The interfacial intermetallic thickness formed on the Ni/Au metallized Cu substrate was determined under the as-soldered and isothermally aged (at 150°C for up to 42 days) conditions. The results of the interfacial intermetallic thickness showed that for the case of the unreinforced solder joint, the intermetallics grew more significantly than that of the composite solder joints, under both as-soldered and isothermally aged conditions. Moreover, the shear test results revealed that the as-soldered and aged composite solder joints exhibited improved ultimate shear strength as compared to that of their unreinforced counterparts. The improvement was observed to be most significant with the addition of 0.05 wt.% of Ni-CNTs, whereby the ultimate shear strength increased by 29% under the as-soldered condition and by 28% after isothermally aged for 42 days. It was concluded that the presence of Ni-CNTs as reinforcements in the Sn-Ag-Cu solder served to inhibit the growth of interfacial intermetallics and also to enhance its mechanical performance.

Effect of welding on the corrosion behavior of X65/Inconel 625 in simulated solution

Due to excellent mechanical properties and corrosion resistance, the carbon steel/nickel-based alloy has huge potential for using in oil and gas industry. The pipes are usually joined by welding. Hence, it is significant to study the effect of welding on the corrosion properties. A literature search indicates that few studies have been conducted on the corrosion properties. Accordingly, in the present work, electrochemical measurements together with immersion tests were used to analyze the corrosion properties of Inconel 625 clad layers and butt-weld metal. The hardness was also determined. The microstructures, morphological features, and the changes observed in the surface composition were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), together with energy-dispersive spectroscopy (EDS). The microstructures of Inconel 625 clad layers and butt-weld metal consist of primary γ-Ni solid solution dendritic, γ/laves interdendritic eutectic. Because of the heat effect induced by multi-pass welding, element segregation and more participation of carbide were observed in the butt-weld metal, which could account for higher hardness and inferior corrosion resistance of the butt-weld metal as compared to the clad layer.

The fabrication of highly conductive and flexible Ag patterning through baking Ag nanosphere−nanoplate hybrid ink at a low temperature of 100 °C

With the aim of developing highly conductive ink for flexible electronics on heat-sensitive substrates, Ag nanospheres and nanoplates were mixed to synthesize hybrid inks. Five kinds of hybrid ink and two types of pure ink were written to square shape on Epson photo paper using rollerball pens and sintered at a low temperature (100℃). The microstructure, electrical resistivity, surface porosity, hardness and flexibility of silver patterns were systematically investigated and compared. It was observed that the optimal mixing ratio of nanospheres and nanoplates was 1:1, which equipped the directly written pattern with excellent electrical and mechanical properties. The electrical resistivity was 0.103 μΩ·m, which was only 6.5 times of bulk silver. The enhancement compared to pure silver nanospheres or nanoplates based ink was owing to the combined action of nanospheres and nanoplates. It was a valued way to prepare Ag nanoink with good performance for printed/written electronics.

Excellent high-temperature magnetic softness for Si-rich Fe-based nanocrystalline alloy with a small amount of Al

In order to estimate the high-temperature soft magnetic properties of nanocrystalline Fe_72.9Al_0.6Si_17.5B₅Cu₁Nb₃, Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb₃ and Fe_72.5Al₁Si_17.5B₅Cu₁Nb₃ alloys, μ¡-T curves were investigated from room temperature up to 700°C. Microstructure properties were analyzed for the alloy with optimum magnetic softness at high-temperature.

Effect of Ni-Coated Carbon Nanotubes on the Creep Behavior of Sn-Ag-Cu Solder by Nanoindentation

In the present study, the powder metallurgy route was used to successfully incorporate Ni-coated carbon nanotubes into Sn-Ag-Cu solder, to form a nanocomposite solder. Nanoindentation tests were performed on both composite and Sn-Ag-Cu solder samples to investigate their creep behaviour at room temperature. Characterization results revealed that with the addition of Ni-coated carbon nanotubes, the creep behaviour of composite solder improved significantly as compared to that of the unreinforced solder alloy. Moreover, increasing the maximum load from 20 mN to 100 mN increased the percentage reduction in creep strain rate from 4% to 28%, for the composite compared to its monolithic counterpart after 300 s of holding.Copyright

Electrochemical Behavior of Welded Joints with 308L Stainless Welding Wire and Low Temperature Transformation Welding Wire

The electrochemical behavior of welded joints with 308L stainless solid welding wire and low temperature transformation welding wire using different welding processes was investigated at ambient temperature in 3.5% NaCl solution using potentiodynamic polarisation technique. Welded joints exhibited different corrosion potential due to the dilutions of alloy elements such as Cr, Ni, Ti, Nb and Mo. To reveal the corrosion resistance of welded joints using different welding processes, some significant characterization parameters such as Ecorr, Eb, △E and Icorr in polarisation curves were analyzed and compared. The result shows that the corrosion resistance of welded joints using low temperature transformation welding wire is better than that using 308L stainless solid welding wire.