Plasma electrolytic oxidation(PEO)was applied using a pulsed unipolar waveform to produce Al_(2)O_(3)−TiO_(2) composite coatings from sol electrolytic solutions containing colloidal TiO_(2) nanoparticles.The sol solut...Plasma electrolytic oxidation(PEO)was applied using a pulsed unipolar waveform to produce Al_(2)O_(3)−TiO_(2) composite coatings from sol electrolytic solutions containing colloidal TiO_(2) nanoparticles.The sol solutions were produced by dissolving 1,3,and 5 g/L of potassium titanyl oxalate(PTO)in a silicate solution.Scanning electron microscopy,energy dispersive spectrometry,X-ray diffraction,and Raman spectroscopy were applied to characterizing the coatings.Corrosion behavior of the coatings was investigated using polarization and impedance techniques.The results indicated that TiO_(2) enters the coating through all types of micro-discharging and is doped into the alumina phase.The higher level of TiO_(2) incorporation results in the decrease of surface micro-pores,while the lower incorporation shows a reverse effect.It was revealed that the higher TiO_(2) content makes a more compact outer layer and increases the inner layer thickness of the coating.Electrochemical measurements revealed that the coating obtained from the solution containing 3 g/L PTO exhibits higher corrosion performance than that obtained in the absence of PTO.The coating produced in the absence of PTO consists of γ-Al_(2)O_(3),δ-Al_(2)O_(3) and amorphous phases,while α-Al_(2)O_(3) is promoted by the presence of PTO.展开更多
The influence of cathodic pulse parameters was evaluated on plasma electrolytic oxidation(PEO)coatings grown on 7075 aluminum alloy in a silicate-based electrolyte containing potassium titanyl oxalate(PTO)using pulsed...The influence of cathodic pulse parameters was evaluated on plasma electrolytic oxidation(PEO)coatings grown on 7075 aluminum alloy in a silicate-based electrolyte containing potassium titanyl oxalate(PTO)using pulsed bipolar waveforms with various cathodic duty cycles and cathodic current densities.The coatings were characterized by SEM,EDS,and XRD.EIS was applied to investigate the electrochemical properties.It was observed that the increase of cathodic duty cycle and cathodic current density from 20%and 6 A/dm^(2) to 40%and 12 A/dm^(2) enhances the growth rate of the inner layer from 0.22 to 0.75μm/min.Adding PTO into the bath showed a fortifying effect on influence of the cathodic pulse and the mentioned change of cathodic pulse parameters,resulting in an increase of the inner layer growth rate from 0.25 to 1.10μm/min.Based on EDS analysis,Si and Ti were incorporated dominantly in the upper parts of the coatings.XRD technique merely detectedγ-Al_(2)O_(3),and there were no detectable peaks related to Ti and Si compounds.However,the EIS results confirmed that the incorporation of Ti^(4+)into alumina changed the electronic properties of the coating.The coatings obtained from the bath containing PTO using the bipolar waveforms with a cathodic duty cycle of 40%and current density values higher than 6 A/dm^(2) showed highly appropriate electrochemical behavior during 240 d of immersion due to an efficient repairing mechanism.Regarding the effects of studied parameters on the coating properties,the roles of cathodic pulse parameters and PTO in the PEO process were highlighted.展开更多
文摘Plasma electrolytic oxidation(PEO)was applied using a pulsed unipolar waveform to produce Al_(2)O_(3)−TiO_(2) composite coatings from sol electrolytic solutions containing colloidal TiO_(2) nanoparticles.The sol solutions were produced by dissolving 1,3,and 5 g/L of potassium titanyl oxalate(PTO)in a silicate solution.Scanning electron microscopy,energy dispersive spectrometry,X-ray diffraction,and Raman spectroscopy were applied to characterizing the coatings.Corrosion behavior of the coatings was investigated using polarization and impedance techniques.The results indicated that TiO_(2) enters the coating through all types of micro-discharging and is doped into the alumina phase.The higher level of TiO_(2) incorporation results in the decrease of surface micro-pores,while the lower incorporation shows a reverse effect.It was revealed that the higher TiO_(2) content makes a more compact outer layer and increases the inner layer thickness of the coating.Electrochemical measurements revealed that the coating obtained from the solution containing 3 g/L PTO exhibits higher corrosion performance than that obtained in the absence of PTO.The coating produced in the absence of PTO consists of γ-Al_(2)O_(3),δ-Al_(2)O_(3) and amorphous phases,while α-Al_(2)O_(3) is promoted by the presence of PTO.
文摘The influence of cathodic pulse parameters was evaluated on plasma electrolytic oxidation(PEO)coatings grown on 7075 aluminum alloy in a silicate-based electrolyte containing potassium titanyl oxalate(PTO)using pulsed bipolar waveforms with various cathodic duty cycles and cathodic current densities.The coatings were characterized by SEM,EDS,and XRD.EIS was applied to investigate the electrochemical properties.It was observed that the increase of cathodic duty cycle and cathodic current density from 20%and 6 A/dm^(2) to 40%and 12 A/dm^(2) enhances the growth rate of the inner layer from 0.22 to 0.75μm/min.Adding PTO into the bath showed a fortifying effect on influence of the cathodic pulse and the mentioned change of cathodic pulse parameters,resulting in an increase of the inner layer growth rate from 0.25 to 1.10μm/min.Based on EDS analysis,Si and Ti were incorporated dominantly in the upper parts of the coatings.XRD technique merely detectedγ-Al_(2)O_(3),and there were no detectable peaks related to Ti and Si compounds.However,the EIS results confirmed that the incorporation of Ti^(4+)into alumina changed the electronic properties of the coating.The coatings obtained from the bath containing PTO using the bipolar waveforms with a cathodic duty cycle of 40%and current density values higher than 6 A/dm^(2) showed highly appropriate electrochemical behavior during 240 d of immersion due to an efficient repairing mechanism.Regarding the effects of studied parameters on the coating properties,the roles of cathodic pulse parameters and PTO in the PEO process were highlighted.
