Effect Of Current Type Research Articles

Effect of Current Type and Density on Tribological Properties of Electrodeposited Ni-Co/MWCNT Nanocomposite Coatings

Effect of Current Type and Density on Tribological Properties of Electrodeposited Ni-Co/MWCNT Nanocomposite Coatings

Experimental Study of Local Scour around Caissons under Unidirectional and Tidal Currents

Local scour around caissons under currents has become one of the main factors affecting the safety of foundation construction and operation in coastal and offshore bridge engineering. Local scour occurs not only in the operation stage, when the caisson has settled into the sediment, but also in the construction stage, when the caisson is suspended in water. In this study, the local scour induced by unidirectional and tidal currents around settled caissons with different cross-sections (circular, square, and diamond) was experimentally investigated. Circular and square caissons were selected to investigate the difference in local scour of suspended caissons under unidirectional and tidal currents. The main findings from the experimental results were: (1) the temporal development of scour under tidal current was slower than that of unidirectional current; (2) the effect of current type can significantly influence the size and location of maximum scour depth around circular and square caissons; (3) the appropriate choice of cross-section could reduce the maximum scour depth around the settled caisson; (4) the maximum scour depth of tidal current was smaller than that of unidirectional current when the caisson was settled into the sediment, while the opposite effect occurred when the caisson was suspended in water.

Effect of current type on microstructure and corrosion resistance of super duplex stainless steel claddings produced by the gas tungsten arc welding process

In this research, super duplex stainless steel filler metals were clad on high strength low alloy steel substrates by the tungsten arc welding process using pulsed and constant currents. To characterize the pulsed current effect, the phase composition and microstructure of the claddings were compared, and the corrosion behavior of the claddings was evaluated using cyclic polarization, electrochemical impedance spectroscopy and critical pitting temperature measurements. The results showed that the slower cooling rate of the constant current cladding led to a higher total reformed austenite content and better corrosion resistance. It was also found that the formation of thermally-activated secondary austenite did not influence the corrosion behavior significantly. The electrochemical impedance spectroscopy indicated that the passive film formed on the pulsed current cladding was more defective. The constant current cladding also showed ten degree higher critical pitting temperature than the one which was produced by pulsed current.

Fabrication of Diamond Dispersed Nickel Composite Coating by Electroplating Method to Enhance the Mechanical Property of Coating

The codeposition behavior of submicron sized diamond with nickel from nickel electrolytes has been investigated. Electroplating of diamond dispersed nickel composites was carried out on a rotating disk electrode (RDE). The effects of current type and current density on the electrodeposited Ni-diamond composite coating were investigated. The effects of pH and surfactants on the composite coating were also investigated. The hardness of coating was measured with varying electroplating conditions. As diamond was incorporated into the coating, the hardness of coating as well as the wear resistance was improved. The surface morphologies of the Ni-diamond composite coatings were observed using FESEM.

The Effects of Current Type and Density on Dishing Phenomena in CMP Process

The dishing phenomena of soft materials in chemical mechanical polishing (CMP) process were problematic in delineating inlaid metal patterns. The inlaid copper structures were fabricated on Si wafer where SiO2 was thermally grown. Seed layer was deposited by thermal evaporate method followed by copper electrodeposition. Copper was electrodeposited with IBM paddle type electroplating machine to obtain uniform thickness of coating. The dishing amounts were measured at various current density and current type. The dishing amounts with pattern density and line width were also measured. The losses of copper were not sensitively dependent on current density however those were dependent on current type. The dishing amount of copper was decreased at high pattern density especially over 50% and increased with line width. Surface topology and grain size of coating were investigated with surface profilometer and FESEM.

Experimental Study of the Microstructure and Stress of Electroplated Gold for Microsystem Applications

Gold, used as an X-ray absorber for lithography and as a structural or conducting material in microsystems, was deposited from a commercially available sulfite electrolyte. The effects of current type and an arsenic additive on the gold microstructure and residual stress were studied. Using a simple bent strip method, good agreement with literature stress values determined via other methods was obtained. Without arsenic, residual stresses are tensile regardless of current type. With 25 ppm arsenic, the stress is compressive for direct current (ca. with pulsed current reducing the stress to compressive; this has been noted previously with thallium as an additive. The addition of arsenic does not appreciably change the film grain size but does lower the twin density and modify texture. Pores were observed in all the gold films, but were larger and less concentrated for films produced with arsenic; for the case of direct current with arsenic, the pores were concentrated at the grain boundaries. Consistencies in the microstructural observations and thin film stress theories are discussed. © 2003 The Electrochemical Society. All rights reserved.