The microarc oxidation（MAO） coatings produced at different current frequencies on AZ91 D magnesium alloys were studied systematically. The morphologies, thickness, corrosion performances, and tribological properties...The microarc oxidation（MAO） coatings produced at different current frequencies on AZ91 D magnesium alloys were studied systematically. The morphologies, thickness, corrosion performances, and tribological properties of the coatings were investigated by the scanning electron microscopy, the electrochemical measurement system, and MS-T3000 friction test rig, respectively. The results show that the structure of the coatings becomes denser, and thickness becomes thinner with the increase of the current frequency. It is also found that the corrosion resistance of the coatings produced at higher frequency is improved greatly and the difference of the corrosion current density becomes small with increasing current frequency, which is similar to that of the coating thickness. The tribological test shows that the friction coefficient decreases with increasing the current frequency and the wear resistance of the coatings is influenced by both the thickness and structures. All these results were explained by analyzing the growing process of the MAO coating.展开更多
Diffraction effects will bring about more difficulties in actuating resonators,which are electrostatically actuated ones with sub-micrometer or nanometer dimensions,and in detecting the frequency of the resonator by o...Diffraction effects will bring about more difficulties in actuating resonators,which are electrostatically actuated ones with sub-micrometer or nanometer dimensions,and in detecting the frequency of the resonator by optical detection.To avoid the effects of diffraction,a new type of nanoelectromechanical systems（NEMS） resonators is fabricated and actuated to oscillate.As a comparison,a doubly clamped silicon beam is also fabricated and studied.The smallest width and thickness of the resonators are 180 and 200 nm,respectively.The mechanical oscillation responses of these two kinds of resonators are studied experimentally.Results show that the resonant frequencies are from 6.8 to 20 MHz,much lower than the theoretical values.Based on the simulation,it is found that over-etching is one of the important factors which results in lower frequencies than the theoretical values.It is also found that the difference between resonance frequencies of two types of resonators decreases with the increase in beam length.The quality factor is improved greatly by lowering the pressure in the sample chamber at room temperature.展开更多
基金Project(11005151)supported by the Young Scientists Fund of the National Natural Science Foundation of ChinaProject(YETP1297)supported by the Beijing Higher Education Young Elite Teacher Project,ChinaProject(BEIJ2014110003)supported by the Undergraduate Research and Innovative Undertaking Program of Beijing,China
文摘The microarc oxidation（MAO） coatings produced at different current frequencies on AZ91 D magnesium alloys were studied systematically. The morphologies, thickness, corrosion performances, and tribological properties of the coatings were investigated by the scanning electron microscopy, the electrochemical measurement system, and MS-T3000 friction test rig, respectively. The results show that the structure of the coatings becomes denser, and thickness becomes thinner with the increase of the current frequency. It is also found that the corrosion resistance of the coatings produced at higher frequency is improved greatly and the difference of the corrosion current density becomes small with increasing current frequency, which is similar to that of the coating thickness. The tribological test shows that the friction coefficient decreases with increasing the current frequency and the wear resistance of the coatings is influenced by both the thickness and structures. All these results were explained by analyzing the growing process of the MAO coating.
基金The National High Technology Research and Development Program of China(863 Program)(No.2007AA04Z301)
文摘Diffraction effects will bring about more difficulties in actuating resonators,which are electrostatically actuated ones with sub-micrometer or nanometer dimensions,and in detecting the frequency of the resonator by optical detection.To avoid the effects of diffraction,a new type of nanoelectromechanical systems（NEMS） resonators is fabricated and actuated to oscillate.As a comparison,a doubly clamped silicon beam is also fabricated and studied.The smallest width and thickness of the resonators are 180 and 200 nm,respectively.The mechanical oscillation responses of these two kinds of resonators are studied experimentally.Results show that the resonant frequencies are from 6.8 to 20 MHz,much lower than the theoretical values.Based on the simulation,it is found that over-etching is one of the important factors which results in lower frequencies than the theoretical values.It is also found that the difference between resonance frequencies of two types of resonators decreases with the increase in beam length.The quality factor is improved greatly by lowering the pressure in the sample chamber at room temperature.
