Formation Of Surface Microtexture By Electrochemical Micromachining Usingcolloidal Crystal As Mask

In the engineering technology,it has been identified that the surface microtexturing can improve wettability,antifriction and wearable ability,lubricity,tribological property and biocompatibility.Through-mask electrochemical micromachining is the mainstream technique in the fabrication technology of the microstructure on the metal parts surface which has some advantages as higher processing accuracy,no wear of tool,no residual stress and deformation and no relation to the hardness of materials.In this study,a simple and effective process which is a nanosphere lithography based on mask of colloid spheres was proposed for machining the microtexturing on the surface of the metal parts.Colloidal crystal masks with different thickness and packing arrangement were fabricated by drop-coating method and electrophoresis-assisted self-assembly process.The effects of concentration of colloidal suspensions and test temperature on the quality and thickness of colloidal mask were studied in the drop-coating process,and the effects of voltage on packing arrangement of colloidal mask in the process of electrophoresis-assisted self-assembly were discussed by the experiments.Monolayer and double-layer colloidal crystals were fabricated by these two processes.At 8 V,the colloidal crystals which were fabricated by electrophoresis-assisted self-assembly process had hexagonal array structure.Up to 10 V,the colloidal crystals showed perfect square array structure.In order to provide theoretical basis for electrolytic etching process using the colloidal crystals as mask,the electrochemical etching process was simulated with COMSOL software.The current density at the bottom of the microspheres was next to zero in the electric field simulation of the current distribution in one time,while anodic dissolution was occurred at the bottom of the microspheres in two times.The colloid mask on the aluminum foil was heated up to 110?to enhance bonding force between the colloid mask and the aluminum foil which was great enough when the aluminum foil was etched in the next process.Microtexturing on the surface of alumina were fabricated by electrochemical etching using the colloidal crystals as mask in the mixed electrolyte of hydrochloric acid and sulfuric acid.The fabricated microtexturing had uniform distribution and size in a mixture of 1mol/L hydrochloric acid and 4mol/L sulfuric acid solutions.The micro-tunneling pits were obtained when the current density was 0.2mA/cm~2 in the electrochemical etching process.