| CHENG Yu-lin,ZHANG Qing-he,CHENG Ying-liang.Corrosion-resistant Coatings on Tantalum Formed by Plasma Electrolytic Oxidation in Phosphate Electrolyte[J],50(6):32-40 |
| Corrosion-resistant Coatings on Tantalum Formed by Plasma Electrolytic Oxidation in Phosphate Electrolyte |
| Received:April 23, 2021 Revised:May 27, 2021 |
| View Full Text View/Add Comment Download reader |
| DOI：10.16490/j.cnki.issn.1001-3660.2021.06.003 |
| KeyWord:tantalum plasma electrolytic oxidation phosphate ceramic coating corrosion resistance |
| Author | Institution |
| CHENG Yu-lin |
School of Materials Science and Engineering, Hunan University, Changsha , China |
| ZHANG Qing-he |
School of Materials Science and Engineering, Hunan University, Changsha , China |
| CHENG Ying-liang |
School of Materials Science and Engineering, Hunan University, Changsha , China |
|
| Hits: |
| Download times: |
| Abstract: |
| This work aims to explore the corrosion resistance of Ta2O5 coatings formed by plasma electrolytic oxidation (PEO) of tantalum in phosphate electrolyte. The phase composition, morphology and elemental composition of the obtained coatings are characterized by XRD, SEM and EDS, respectively. The corrosion resistance is investigated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). The PEO coatings are composed of crystalline Ta2O5. A thin film with nodules is formed at the initial stage of PEO, and later changes to a grooved structure. The potentiodynamic polarization tests are performed in 3.5% NaCl solution, and the results show that the corrosion current density of the coatings is about 4 orders of magnitude lower than that of the substrate. The corrosion potential of the PEO coating formed in 600 s was increased by ~1.3 V compared with the un-treated substrate, and the corrosion current density is 3.7´10–10 A/cm2, showing a protection efficiency of 99.97%; the corrosion potential of the 1200 s PEO coating was increased by ~1.4 V, and the current density is 1.46´10–10 A/cm2, showing a protection efficiency of 99.99%. During 160 days of immersion tests in 3.5% NaCl solution, a thin oxide coating has formed on the surface of bare tantalum and the impedance value increases constantly after immersion for the initial 30 days, which demonstrates a protective effect on substrate to some extent. However, when the coating formed by PEO for 600 s was immersed in the solution, the impedance in the low-frequency region dropped significantly after 3 days. As the immersion time extended, the impedance of the coating continued to decrease. However, the value of the charge transfer impedance is still an order of magnitude higher than that of the un-treated tantalum after 160 days of immersion. It shows that the PEO coating formed on tantalum in the phosphate electrolyte has good corrosion resistance, and PEO can greatly improve the corrosion resistance of tantalum. |
| Close |
|
|
|