Hansong Li

Significance of Dimple Parameters on the Friction of Sliding Surfaces Investigated by Orthogonal Experiments

Surface texturing has proven to be an effective method to improve tribological performance of sliding surfaces. The pattern of microdimples is the most popular surface texture because it is supposed to obtain additional hydrodynamic pressure easily. In order to evaluate the significance of the dimple parameters, including dimple diameter, depth, and area ratio, to the frictional performance, the dimple patterns with dimple diameter from 50 to 300 μm, dimple depth from 5 to 20 μm, and area ratio from 5 to 20% were manufactured on chromium-coated specimens by through-mask electrochemical micromachining. Experiments were designed using an L 16 (4 5 ) orthogonal array, which contained the above three factors and four levels for each factor. The frictional tests on the above-textured specimens against the specimens of cast iron with oil lubrication were carried out under the contact pressures of 0.2 and 1 MPa and sliding velocities of 0.1 s and 0.5 m/s. The range analysis showed that the optimum dimple pattern was that with dimple diameter of 100–200 μm, dimple depth of 5–10 μm, and area ratio of 5%, which induced the friction reduction up to 77.6% compared to that of untextured surfaces. Both the range analysis and analysis of variance suggested that dimple area ratio is the most important parameter influencing friction coefficient under the test condition of this research.

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.

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.

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.

Distribution Manner of Compaction Circular Cylinders in Through-Active-Mask Electrochemical Machining

Electrochemical machining is widely used in the processing of difficult-to-machine metal materials. And through-mask electrochemical machining is a very important technology in the processing array structure of difficult-to-cut metal materials. Traditional through-mask electrochemical machining always uses a photoresist as the mask. The production process of a mask is complicated, and the mask cannot be reused. In this paper, through-active-mask electrochemical machining to process array structure in difficult-to-machine metal materials was investigated. Compared with traditional electrochemical machining masks, a copper-clad laminate is used to make the mask by mechanical machining in through-active-mask electrochemical machining. Also, the mask does not stick together with the workpiece but covers the workpiece by mechanical compaction, so the mask can be reused. In order to ensure the mask is in close contact with the workpiece, we need to arrange many compaction circular cylinders within the flow channel. The influences on electrolyte flow of compaction circular cylinders were investigated. The distribution of the compaction circular cylinders affects the electrolyte flow state, thereby affecting the processing. By analyzing the electrolyte flow state for the different distributions of compaction circular cylinders, one can find the best distribution of compaction circular cylinders for the required processing.

Structural responses of metallic glasses under neutron irradiation

Seeking nuclear materials that possess a high resistance to particle irradiation damage is a long-standing issue. Permanent defects, induced by irradiation, are primary structural changes, the accumulation of which will lead to structural damage and performance degradation in crystalline materials served in nuclear plants. In this work, structural responses of neutron irradiation in metallic glasses (MGs) have been investigated by making a series of experimental measurements, coupled with simulations in ZrCu amorphous alloys. It is found that, compared with crystalline alloys, MGs have some specific structural responses to neutron irradiation. Although neutron irradiation can induce transient vacancy-like defects in MGs, they are fully annihilated after structural relaxation by rearrangement of free volumes. In addition, the rearrangement of free volumes depends strongly on constituent elements. In particular, the change in free volumes occurs around the Zr atoms, rather than the Cu centers. This implies that there is a feasible strategy for identifying glassy materials with high structural stability against neutron irradiation by tailoring the microstructures, the systems, or the compositions in alloys. This work will shed light on the development of materials with high irradiation resistance.