Influence of the aluminum surface on the final results of a two-step anodizing

1050 Aluminum alloy sheets were used to analyze the influence of a surface treatment on the characteristics of the alumina layer formed in a two-step anodizing. The study was mainly focused on two pretreatment steps, electropolishing and acid etching, as well as on the intermediate stripping step. The pretreatment procedure was optimized by accounting for the chemical nature of the substrate, with the results indicating that additional pretreatment steps enhanced the self-ordered porous arrangement. The E-t curves recorded during the experiments demonstrated that the best alumina layers were obtained when the first barrier layer had a high resistance; i.e., a high anodizing potential. The application time of the stripping step was optimized to clean the surface from alumina remains, without damaging the aluminum substrate. By optimizing all of these experimental conditions, we were able to obtain porous anodic aluminum oxide layers displaying ordered domains several hundreds of nanometers in length.     

PLANAR COPPER PLATING AND ELECTROPOLISHING TECHNIQUES

Electrochemical mechanical deposition (ECMD) is a novel technique that has the ability to deposit planar conductive films on non planar substrate surfaces. This technique involves electrochemical deposition (ECD) while simultaneously polishing the substrate surface. Preferential deposition of the conductor into the cavities on the substrate surface may be achieved through two different mechanisms. The first mechanism is more mechanical in nature and it involves material removal from the top surface. The second mechanism is more chemical in nature, and it involves enhancing the deposition into the cavities where mechanical sweeping does not reach and reducing deposition onto surfaces that are swept. In this study we demonstrate that in an ECMD process, low-pressure mechanical sweeping of the wafer surface during copper plating can establish a differential in the activity of the organic accelerator species between the surface and the cavity regions of the substrate and thus give rise to bottom-up filling in even the lowest aspect-ratio cavities. Planar layers obtained by the ECMD technique have been successfully employed in an electrochemical polishing technique for stress-free removal of Cu.     

Electrochemical polishing of ITO films

Oxalic acid and tartaric acid were used to electrochemically treat the surface of indium tin oxide (ITO) films. To improve the surface of ITO films, the applied voltage was found via potentiodynamic technique. By controlling the concentration of oxalic acid and tartaric acid, the surface can be effectively planarized via the formation of a passive layer. The composition of this passive layer might be SnO₂ according to XPS analysis and potential-pH diagrams. The best treatment with root-mean-squared roughness less than 1.0 nm can be obtained by electropolishing at 0.65 V in 3 wt% tartaric acid.     

Electropolishing of 304 stainless steel: Interactive effects of glycerol content, bath temperature, and current density on surface roughness and morphology

In this study, surface roughness of 304 stainless steel (304SS) varying from ca. 7 to 45 nm can be controlled by changing electropolishing variables in glycerol-containing baths. On the basis of the adsorbate-acceptor mechanism and the model for preferential adsorption of shielding molecules, incorporating the molecular interaction concept is helpful to explain the interactive effects of glycerol content, bath temperature, and current density on the surface roughness (Ra) and morphologies of 304SS. In order to easily understand how to control the surface roughness of 304SS in the glycerol-containing electrolyte, a simplified scheme integrating the above two mechanisms was proposed. From the atomic force microscopy (AFM) analyses, a rough surface is easily obtained by electropolishing at high bath temperatures, which endows the 304SS substrate with pores.     

Electropolishing and passivation of NiTi shape memory alloy

Electropolishing of NiTi alloy has been investigated. The influence of polishing bath composition and the operating conditions instead of the conditions of the process on the quality of the surface, evaluated by AFM and SEM methods, was established. Morphologically uniform surfaces were obtained only in the case of solutions containing hydrofluoric and sulfuric acids. Electropolished samples were sterilized and thermally passivated, then their corrosion resistance was measured in Tyrode's physiological solution. It was established that already after the electropolishing the corrosion resistance of NiTi alloy increases due to the spontaneously formed TiO₂ layer. The increase of the thickness of the layer during sterilization and thermal passivation causes further increase in the corrosion resistance.     

Characterisation of surface oxidation of nickel-titanium alloy by ion-beam and electrochemical techniques

The passivating effects produced on Ni₄₉Ti₅₁ (at.%) shape memory alloy by electropolishing in methanol-sulphuric acid electrolyte or thermal treatment in air are investigated with ion-beam techniques (secondary ion mass spectrometry (SIMS) and mass resolved ion scattering spectrometry (MARISS)) and electrochemical techniques (polarisation curves, photocurrent spectroscopy and impedance). Electropolishing produces a limited passivation due to formation of a thin layer of amorphous TiO₂, which causes only a slight hindrance to the oxygen evolution reaction. Thermal treatment in air at 450 °C causes a more substantial passivation due to formation of a thick oxide layer, estimated at about 80 nm for a 16 h treatment on the basis of weight increase, disregarding roughness. Data indicate that the film produced by thermal oxidation has probably a duplex structure, with a porous outer layer with inclusions of Ni species and a compact inner layer, in contact with the substrate, consisting of (essentially) nickel free TiO₂ rutile.     

Effect of surface treatments on the strength of carburized gears

This paper deals with effects of surface treatment on the bending fatigue strength of SCM415 carburized spur gears. The test gears are treated by the combination of shot peening, chemical polishing and electropolishing after carburization. The fatigue tests demonstrate that the strength is sensitive to the surface condition of tooth fillet and the removal of the nonmartensitic layer caused by decarburization is considerably effective in enhancing the strength. In the first part of this paper, the influence of surface treatments such as shot peening, chemical polishing and electropolishing on the strength enbancement for carburized gears are summarized and discussed. In the second part, the crack lengths are calculated from the fatigue test results for the carburized and surface-treated gears, and the effect of surface treatments is discussed from the view point of fracture mechanics.     

<Emphasis Type="Italic">Continuous Secondary Ultrasonic Electropolishing of an SKD61 Cylindrical Part</Emphasis>

An effective ultrasonic-aided electropolishing system using low-cost electrodes for polishing cylindrical parts is developed. The process can be integrated with the primary processes of traditional turning, drawing, form rolling, or extrusion to achieve a good surface finish for moulds. Ultrasonic energy is applied to the electrolyte for residue discharge during electropolishing. Both continuous and pulsed direct current are tested in the study. The controlled factors include the chemical composition and concentration of the electrolyte, the electrolyte temperature, the flowrate of electrolyte, the initial gap width, and the rotational speed of the workpiece. The experimental parameters are the frequency and power of the ultrasonic vibration, electrical current density, pulse period, rotational speed of the electrode, the electrode feedrate, and the electrode geometry. The incorporation of ultrasonics is found to be more effective than the use of pulsed current, without sacrificing the polishing time. An average surface roughness of 0.3 μm can be obtained by this method. ID="A1"Correspondance and offprint requests to: Professor H. Hocheng, Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu, Taiwan. E-mail: hocheng@pme.nthu.edu.tw     

Artifacts introduced by ion milling in Al-Li-Cu alloys

Ion milling is commonly used to prepare specimens for observation under transmission electron microscope (TEM). This technique sometimes introduces artifacts in specimens contributing to misleading interpretation of TEM results as observed in the present investigation of Al-Li-Cu alloys. This type of alloy, in general, contains several kinds of precipitates, namely δ′ T₁, and θ′. It is found that ion milling even for a short time produces drastic changes in the precipitate characterics as compared to standard electropolishing methods of specimen preparation for TEM. Careful analysis of selected area diffraction patterns and micrographs shows that after ion milling δ′ precipitates are very irregular, whereas other precipitates coarsen and they are surrounded by misfit dislocations. In situ hot-stage TEM experiments were performed to relate the microstructure to that observed in the ion-milled specimen. Results and causes of ion milling effects on the microstructure are discussed in relation to standard electropolishing techniques and in situ hot-stage experiment.     

Electropolishing of AISI-304 stainless steel for protection against SRB biofilm

Electropolishing treatment (EP) can be used to remove the biofilm formed on AISI-304 stainless steel surface and protect it against bacterial colonization. High levels of both smoothness and brightness of AISI-304 stainless steel surfaces can be attained by using electropolishing technique, where the sample was fixed as anode and a suitable current was applied into electrolytic cell containing H₃PO₄. AISI-304 stainless steel was exposed to stabilized mixed culture of sulfate reducing bacteria (SMC-SRB) under different conditions as, temperature, pH, salinity, incubation time and inoculum size. The present study recorded the main indicators of bacterial activity such as S⁻⁻, Fe⁺⁺, most probable number (MPN) of SRB and weight loss (corrosion rate) by milinches per year (mpy). The results revealed that the bacterial counts were obviously decreased under all conditions of bacterial biofilm formation after electropolishing treatment.