Fengzhang Ren

Cyanide-free silver electroplating process in thiosulfate bath and microstructure analysis of Ag coatings

Abstract Cyanide-free silver electroplating was conducted in thiosulfate baths containing AgNO 3 and AgBr major salts, respectively. The effects of major salt content and current density on surface quality, deposition rate and microhardness of Ag coatings were investigated. The optimized electroplating parameters were established. The adhesion strength of Ag coating on Cu substrate was evaluated and the grain size of Ag coating was measured under optimized electroplating parameters. The optimized AgNO 3 content is 40 g/L with current density of 0.25 A/dm 2 . The deposited bright, smooth, and well adhered Ag coating had nanocrystalline grains with mean size of 35 nm. The optimized AgBr content was 30 g/L with current density of 0.20 A/dm 2 . The resultant Ag coating had nanocrystalline grains with mean size of 55 nm. Compared with the bath containing AgBr main salt, the bath containing AgNO 3 main salt had a wider current density range, and corresponding Ag coating had a higher microhardness and a smaller grain size.

Microstructure and Hardness of Laser Shocked Ultra-fine-grained Aluminum

Ultra-fine-grained commercial purity aluminum was produced by severe cold rolling, annealing and then straining at ultra-high rate by a single pass laser shock. Resulted microstructure was investigated by transmission electron microscopy. Microhardness of annealed 0.6 pm ultra-fine grained aluminum increased by 67% from 24 to 40 HV. Many 0.3 pm sub-grains appeared at the shock wave center after a single pass laser shock, while high density dislocation networks were observed in some grains at the shock wave edges. Accordingly, microhardness at the impact center increased by 37.5% from 40 to 55 HV. From the impact center to the edge, microhardness decreased by 22% from 55 to 45 HV.

Electrotribological behavior of Cu−Ag−Zr contact wire against copper-base strip

Cu−Ag−Zr alloy has an excellent combination of mechanical strength and electrical conductivity, and is a promising contact wire material for high-speed electrified railways. An investigation of the electritrobological behavior of Cu−Ag−Zr wire is presented here. Wear tests are conducted under laboratory conditions with a specified sliding wear tester that simulated train motion under an electrical current applied across the sliding interface. The Cu−Ag−Zr alloy wire is slid against a copper-based powder metallurgy strip used in railway systems under unlubricated conditions. Worn surfaces of the Cu−Ag−Zr alloy wire are analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectrum (EDS). Within the studied range of electrical current, normal pressure, and sliding speed, the wear rate increases with increasing electrical current and sliding distance. Adhesive wear, abrasive wear, and electrical erosion are the dominant mechanisms during the electrical sliding processes. Compared with a Cu−Ag contact wire under the same test conditions, the Cu−Ag−Zr alloy wire has much better wear resistance.

Role of trivalent antimony in the removal of As, Sb, and Bi impurities from copper electrolytes

The role of trivalent antimony was investigated in removing As, Sb, and Bi impurities from a copper electrolyte. Purification experiments were carried out by adding a various concentrations of Sb(III) ions in a synthetic electrolyte containing 185 g/L sulfuric acid, 45 g/L Cu2+, 10 g/L As, and 0.5 g/L Bi under stirring at 65°C for 2 h. The electrolyte was filtered, and the structure, morphology and composition of the precipitate were analyzed by means of chemical analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and IR spectroscopy. The precipitate is composed of irregular lumps which are agglomerated by fine dendritic and floccus particles, and it mainly consists of As, Sb, Bi, and O elements. Characteristic bands in the IR spectra of the precipitate are As-OX (X=As, Sb, Bi), Sb-OY (Y=Sb, Bi), O-As-O, As-OH, Sb-OH, and O-H. The precipitate is a mixture of microcrystalline SbAsO4, (Sb,As)2O3, and amorphous phases. As, Sb, and Bi impurities are effectively removed from the copper electrolyte by Sb(III) ions attributing to these precipitates.

Evaluation of Ni Film Interfacial Energy Release Rate on Titanium and Stainless Steel Substrates

An expression including the effect of residual stress on the interfacial energy release rate is proposed for peeling experiments according to the energy-balance argument. The influence of residual stress on the external work is also contained in the expression. Two numerical methods are employed to evaluate the values of the work expenditureGdb, which is the actual energy dissipated during bending of the peel arm near the peel front. The peeling method is employed to test the interfacial energy release rates,G, for Ni films on Titanium and stainless steel substrates. The results indicate that the value ofG for Ni films on stainless steel substrate is about 5.47–6.03 N/m, while 5.23–6.71 N/m for Ni films on titanium substrate; the interfacial energy release rates,G, do not depend on the residual stress in film, film thickness nor peel angle. The effect of residual stress in film on peel strengthP/h is also discussed.

Microstructure Evolution and Microhardness of Ultrafine-grained High Carbon Steel during Multiple Laser Shock Processing

Surface microstructure and microhardness of (ferrite+cementite) microduplex structure of the ultrafine-grained high carbon steel after laser shock processing (LSP) with different impact times were investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and microhardness measurements. Equiaxed ferrite grains were refined from 400 to 150 nm, and the cementite lamellae were fully spheroidized, with a decrease of the particle diameter from 150 to 100 nm as the impact times increased. The cementite dissolution was enhanced significantly. Correspondingly, the lattice parameter of α-Fe and microhardness increased with the impact times.

Additive effects on tin electrodepositing in acid sulfate electrolytes

The effects of additives on the stannous reduction of an acid sulfate bath were investigated using cyclic and linear sweep voltammetry, electrochemical impedance spectroscopy (EIS), and microstructure analysis. In the absence of additives, tin coatings are rough, and the tin electrodepositing is a single-step reduction process accompanied by hydrogen gas evolution. The addition of tartaric acid produces a slight reduction in the peak current of stannous reduction and has an appreciably positive effect on the stability of the acidic tin bath. Both benzylidene acetone and polyoxyethylene octylphenol ether hinder the stannous reduction and greatly suppress the hydrogen gas evolution. Formaldehyde slightly decreases the peak current density of stannous reduction and serves as an auxiliary brightener in the acid sulfate bath. The presence of mixed additives greatly suppresses the stannous reduction and hydrogen gas evolution and consequently produces a significantly smoother and denser tin coating. The (112) crystal face is found to be the dominant and preferred orientation of tin deposits.

Electrotribological property of the Cu−Ag−Cr alloy with high-strength and high-conductivity

By means of a vacuum induction furnace, a Cu−Ag−Cr alloy was produced. The electrotribological property and mechanism of the Cu−Ag−Cr alloy wear studied via wear property tests, scanning electron microscope (SEM), energy dispersive X-ray spectrum (EDS) and transmission electron microscopy (TEM). Wear tests were conducted with a specially designed sliding wear tester, which simulated the tribological conditions of sliding current collectors on contact wires in a railway system. The alloy wire was slid against a copperbased powder metallurgy strip under non-lubricated conditions. The results showed that the wear rate of Cu−Ag−Cr alloy increases as the sliding speed increases under a normal load. Adhesive wear, abrasive wear, and electrical erosion wear are the governing wear mechanisms under the electrical current sliding processes. Under the same conditions, the wear resistance of the Cu−Ag−Cr alloy is 2–3 times that of the Cu−Ag alloy.

Electron theory based explanation and experimental study on deformation behavior of Cu/Ni multilayers

Cu/Ni multilayers with various defined thickness of Cu and Ni layers were electrodeposited on low carbon steel substrates. Hardness measurements indicated that the increase in yield strength (one-third of hardness) with a decrease of layer thickness for Cu/Ni multilayers with single layer thickness at sub-micron length scale could be described by the Hall-Petch formula of the dislocation pile-up model. In the regime of few tens to a hundred nanometers of single layer thickness, the dislocation pileup-based Hall-Petch model broke down. This could be explained quantitatively according to the criterion condition on the limit size of dislocation derived from a modified Thomas-Fermi-Dirac electron theory.

Role of Sb(V) in removal of As, Sb and Bi impurities from copper electrolyte

Abstract The function mechanism of Sb(V) in As, Sb and Bi impurities removal from copper electrolyte was investigated by adding Sb(V) ion in a synthetic copper electrolyte containing 45 g/L Cu2+, 185 g/L H2SO4, 10 g/L As and 0.5 g/L Bi. The electrolyte was filtered, and the precipitate structure, morphology and composition were characterized by chemical analysis, SEM, TEM, EDS, XRD and FTIR. The results show that the precipitate is in the shape of many irregular lumps with size of 50–200 μm, and it mainly consists of As, Sb, Bi and O elements. The main characteristic bands in the FTIR spectra of the precipitate are As—O—As, As—O—Sb, Sb—O—Bi, Sb—O—Sb and Bi—O—Bi. The precipitate is the mixture of microcrystalline of AsSbO4, BiSbO4 and Bi3SbO7 by XRD and electronic diffraction. The removal of As, Sb and Bi impurities by Sb(V) ion can be mainly ascribed to the formation of antimonate in copper electrolytes.