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<p>A custom micro-arc oxidation (MAO) apparatus is employed to produce coatings under optimized constant voltage–current two-step power supply mode. Various analytical techniques, including scanning electron microscopy, confocal laser microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and electrochemical analysis, are employed to characterize MAO coatings at different stages of preparation. MAO has MgO, hydroxyapatite, Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>, and Mg<sub>2</sub>SiO<sub>4</sub> phases. Its microstructure of the coating is characterized by "multiple breakdowns, pores within pores", and "repaired blind pores". The porosity and the uniformity of MAO coating first declines in the constant voltage mode, then augments while the discharge phenomenon takes place, and finally decreases in the repair stage. These analyses reveal a four-stage growth pattern for MAO coatings: anodic oxidation stage, micro-arc oxidation stage, breakdown stage, and repairing stage. During anodic oxidation and MAO stages, inward growth prevails, while the breakdown stage sees outward and accelerated growth. Simultaneous inward and outward growth in the repair stage results in a denser, more uniform coating with increased thickness and improved corrosion resistance.</p>

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Growth pattern of MAO coating under constant voltage–current two-step power mode

  • 期刊论文

  • 发表日期：

    2025年3月22日

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  • Shu-fan Zhou,
  • Liang-yu Chen,
  • Wei-gang Lv,
  • Jun-jie Gu,
  • Fei Ye,
  • Dubovyy Oleksandr,
  • Sheng Lu,
  • Ze-xin Wang

摘要

A custom micro-arc oxidation (MAO) apparatus is employed to produce coatings under optimized constant voltage–current two-step power supply mode. Various analytical techniques, including scanning electron microscopy, confocal laser microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and electrochemical analysis, are employed to characterize MAO coatings at different stages of preparation. MAO has MgO, hydroxyapatite, Ca3(PO4)2, and Mg2SiO4 phases. Its microstructure of the coating is characterized by "multiple breakdowns, pores within pores", and "repaired blind pores". The porosity and the uniformity of MAO coating first declines in the constant voltage mode, then augments while the discharge phenomenon takes place, and finally decreases in the repair stage. These analyses reveal a four-stage growth pattern for MAO coatings: anodic oxidation stage, micro-arc oxidation stage, breakdown stage, and repairing stage. During anodic oxidation and MAO stages, inward growth prevails, while the breakdown stage sees outward and accelerated growth. Simultaneous inward and outward growth in the repair stage results in a denser, more uniform coating with increased thickness and improved corrosion resistance.