Ningsong Qu

Improving the Localization of Surface Texture by Electrochemical Machining with Auxiliary Anode

Surface texture can be generated by through-mask electrochemical micromachining. However, the machining localization deteriorates by the lateral undercutting under the mask. In this article, the auxiliary anode was consisted in the mask to reduce the lateral undercutting to improve localization of the surface texture. Numerical simulation of the current density distribution in the interelectrode gap was used to theoretically verify the proposed method, and the effect of the auxiliary anode on the localization was investigated experimentally. The experimental results indicated that the machining localization could be significantly improved by the auxiliary anode, and the etch factor was decreased with the increasing machining voltage.

Nanocrystaline Electroforming Process

Abstract This study focuses on nanocrystalline electroforming for the improvement of the properties of deposited parts in precision and micro fabrications. Experiments were conducted to refine the grain size and understand the effects of the grain size on properties of deposited metals. It has been found that high frequency pulse current, strong electrolyte flushing and some additive significantly refined the crystal grain and reduced average sizes of grains down to 20nm. The reduction of grain sizes has been found to offer substantial gains in the properties of the deposited metal such as the hardness and the corrosion resistance.

Effect of reverse pulse current on the internal stress of electroformed nickel

Abstract In recent years, much attention has been paid to electroforming as a high-technology manufacturing technique for micro-devices. However, internal stress is one of the major problems required to be solved before this technique can be used widely for the micro-forming of premium products. There have been a lot of research effort in controlling internal stress, most of which has focused on adjusting the bath, although, this approach has not lead to a significant improvement in the quality of the deposit. In the present paper, the use of reverse pulse current in electroforming has been proposed to enhance the quality of the deposit. A series of experiments have been carried out to study the effect of reverse pulse current on the internal stress of electroformed nickel, a significant reduction in internal stress being achieved.

The Fabrication and Application of a PDMS Micro Through-Holes Mask in Electrochemical Micromanufacturing

The electrochemical micromanufacturing process, as a key micromanufacturing technology, plays an important role in diverse industries. In this paper, polydimethylsiloxane (PDMS) is employed as a mask in the electrochemical micromanufacture of microstructures because of its chemical resistance, low cost, flexibility, and high molding capability. A new method for fabricating a PDMS micro through-holes mask is proposed. In this method, a thin resist film is employed to enhance the adhesion between the substrate and the SU-8 pillar array which is used as a mold. A vacuum-aided process is used to inject the PDMS gel into the SU-8 mold and the PDMS micro through-holes mask can be peeled off from the SU-8 mold when the gel is cured. Experiments were conducted to verify the feasibility of the proposed approach and PDMS microholes of various shapes were obtained. The PDMS mask can then be successfully applied in the electrochemical micromanufacturing process to generate microstructures and microdimple and embossment arrays have been successfully demonstrated. Furthermore, the PDMS mask can be reused, as it is not damaged during the manufacturing process.

Abrasive polishing assisted nickel electroforming process

This paper presents a hybrid process combining electroforming technique and abrasive polishing. In a specifically developed equipment the spherical ceramic particles between the cathode mandrel and the anode are forced to continuously polish the deposition surface during nickel electrodepositing. The abrasive polishing can effectively remove the pinholes and nodules, and positively affect the crystal nucleation and therefore refine the grains and speed up the deposition process. Smooth deposition surface of Ra 0.012 μm, compact nickel deposits with the grain size of less than 80nm and the significantly improved mechanical properties have been experimentally obtained.

A Study of Electrochemical Machining of Ti-6Al-4V in NaNO 3 solution

The titanium alloy Ti-6Al-4V is used in many industries including aviation, automobile manufacturing, and medical equipment, because of its low density, extraordinary corrosion resistance and high specific strength. Electrochemical machining (ECM) is a non-traditional machining method that allows applications to all kinds of metallic materials in regardless of their mechanical properties. It is widely applied to the machining of Ti-6Al-4V components, which usually takes place in a multicomponent electrolyte solution. In this study, a 10% NaNO3 solution was used to make multiple holes in Ti-6Al-4V sheets by through-mask electrochemical machining (TMECM). The polarization curve and current efficiency curve of this alloy were measured to understand the electrical properties of Ti-6Al-4V in a 10% NaNO3 solution. The measurements show that in a 10% NaNO3 solution, when the current density was above 6.56 A·cm−2, the current efficiency exceeded 100%. According to polarization curve and current efficiency curve, an orthogonal TMECM experiment was conducted on Ti-6Al-4V. The experimental results suggest that with appropriate process parameters, high-quality holes can be obtained in a 10% NaNO3 solution. Using the optimized process parameters, an array of micro-holes with an aperture of 2.52 mm to 2.57 mm and maximum roundness of 9 μm were produced using TMECM.

Synthesis of Nanocrystalline Nickel in Pulse Deposition

SUMMARY This paper describes a new method developed to synthesise bulk nanocrystalline nickel. A high frequency pulse current and high deposit current density were employed to increase the deposit cathodic overpotential and the nucleation rate. With increasing peak current density, the deposit grain sizes was found to decreased markedly, e.g. average grain sizes ranging from 200 to 50 nm were determined when the peak current density varied from 60 to 300 A dm2 at the on-time of 10 μs and the off-time of 90 μs. In the saccharin-containing electrolyte, the deposit grain size ranges from 80 to 15 nm under the same conditions. The hardness of the nickel deposits was examined when the average current density ranged from 2 to 40 A dm 2.

Mechanical Properties of Electrodeposited Nanocrystalline Nickel

SUMMARY In this paper, dense bulk nanocrystalline (nc) nickel electrodeposits with various grain sizes were produced by using high frequency pulse current and strong electrolyte flushing. The effects of the grain sizes on the mechanical properties were discussed for room and a medium temperature. It was found that the properties of the deposited nickel such as microhardness, corrosion resistance and yield stress (at room temperature and 473 K) were improved substantially with the decrease in the grain size. A deviation of yield stress from the Hall-Petch relationship for nc nickel was observed when the grain sizes were decreased to less than 70 nm at room temperature. A low yield stress value of nc nickel was obtained at a temperature of 673 K as a result of its thermodynamic instability.

Fabrication of graded nickel quasicrystal composite by electrodeposition

SUMMARY Functionally graded coatings with a gradual change in composition and microstructure can perform specific functions and meet stringent performance requirements. A new graded composite coating, nickel-quasicrystal, was examined in this paper. It was found that the volume percentage of embedded quasicrystal particles in the composite increased with an increase in current density up to 10 A dm2. A maximum volume percentage quasicrystal particles of 48.2% was obtained at the current density of 10 A dm−2, an electrolyte particle content of 50 g dm3, agitation speed of 400 rpm, and particle size of 5 μm Graded Ni-quasicrystal composite coatings were produced by manipulating the current density and the deposition time, and their hardness and composition were evaluated.

Note: Electrochemical etching of cylindrical nanoprobes using a vibrating electrolyte

An electrochemical etching process using a vibrating electrolyte of potassium hydroxide to prepare tungsten cylindrical nanotips is developed. The vibrating electrolyte eases the effects of a diffusion layer and extends the etching area, which aid in the production of cylindrical nanotips. Larger amplitudes and a vibration frequency of 35 Hz are recommended for producing cylindrical nanotips. Nanotips with a tip radius of approximately 43 nm and a conical angle of arctan 0.0216 are obtained.