Plasma electrolytic oxidation of magnesium by sawtooth pulse current
Plasma electrolytic oxidation of magnesium by sawtooth pulse current
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DOI：
10.1016/j.surfcoat.2021.127938
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发表时间：
2022-01-15
影响因子：
5.4
通讯作者：
Yerokhin, Aleksey
中科院分区：
文献类型：
--
作者：
Guo, Yue;Rogov, Aleksey;Yerokhin, Aleksey
采用等离子体电解氧化法在纯镁表面制备了Mg2SiO4涂层。同时采集电压、电流和光发射信号，推导并分析PEO过程中系统电流和放电粒子数密度的演变规律，同时采用光发射光谱技术对等离子体物种进行识别。使用扫描电子显微镜进行涂层形态表征。通过X射线衍射确定相组成。腐蚀性能进行了评估，电化学阻抗谱在不同时期暴露于腐蚀性介质（0.5重量% NaCl）。结果表明，在脉冲单极和反向电流制度的微放电特性和涂层形态的控制，双脉冲的应用程序允许。结果进一步表明，施加具有负斜坡的阳极氧化脉冲促进涂层形成期间的缺陷愈合，导致产生具有较低孔隙率和镁基底的较慢降解速率的更均匀的PEO涂层。涂层电阻随浸泡时间的稳定衰减提供了控制镁降解的可能性，从而在需要可预测的镁溶解速率的应用中优化组件寿命，例如金属结构和可吸收生物医学植入物的牺牲阳极保护。
Mg2SiO4 coatings were formed on cp-Mg by Plasma Electrolytic Oxidation (PEO) using electrical regimes based on sawtooth anodic current pulses with extended ascending or descending segments (ramps). Voltage, current and light emission signals were simultaneously acquired to derive and analyse the evolution of system current and discharge population density during PEO process, while optical emission spectroscopy was employed for identification of plasma species. Coating morphological characterisation was carried out using Scanning Electron Microscopy. Phase composition was identified by X-ray diffraction. The corrosion performance was evaluated with Electrochemical Impedance Spectroscopy at various periods of exposure to corrosive media (0.5 wt% NaCl). It was shown that the application of sawtooth pulses allowed the controlling of microdischarge characteristics and coating morphology in both pulsed unipolar and reversed current regimes. Results further demonstrate that the application of anodic sawtooth pulses with the negative ramp facilitated defect healing during coating formation leading to production of more uniform PEO coatings with lower porosity and a slower degradation rate of magnesium substrate. A steady decay in the coating resistance with immersion time provides a possibility for controlling magnesium degradation and thereby for optimisation of component lifetime in applications where predictable Mg dissolution rate is required, such as sacrificial anodic protection of metallic structures and resorbable biomedical implants.