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<p>Phosphate-based electrolytes are among the most efficient media for microarc oxidation (MAO), as they enable rapid coating growth at low breakdown voltages and short formation times. In this study, MAO coatings were fabricated on Ti6Al4V titanium alloy using four different phosphate-based electrolytes, including several common and representative orthophosphates and polyphosphates. The aim was to investigate how electrolyte composition influences the coating formation mechanism, microstructure, and functional properties. Discharge characteristics and plasma behaviours during the MAO process were monitored using optical emission spectrometry and real-time surface state analysis. All resulting coatings exhibited n-type semiconducting behaviour and were primarily composed of TiO<sub>2</sub>, with rutile identified as the dominant crystalline phase. Coating growth occurred predominantly in the outward direction, driven by the combined effects of substrate oxidation and deposition of phosphate compounds. Photocatalytic degradation tests using methyl orange showed that all coatings achieved degradation efficiencies exceeding 40% within 6&#xa0;h. Among the tested electrolytes, coatings formed in Na<sub>5</sub>P<sub>3</sub>O<sub>10</sub> solutions demonstrated the highest corrosion and wear resistance, with a corrosion current density of 2.28 × 10<sup>–9</sup> A/cm<sup>2</sup> and a wear rate of 4.10 × 10⁻<sup>3</sup> mm<sup>3</sup>/(N·m). The results indicate that polyphosphates increase breakdown voltage and accelerate coating growth, making them suitable for short-duration processes. In contrast, orthophosphates reduce breakdown voltage, promoting sustained densification over longer treatment periods. Furthermore, phosphates with a molecular weight of three or more emerge as optimal electrolytes for fabricating functional MAO coatings on Ti6Al4V alloys.</p>

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A comprehensive understanding of microarc oxidation coating for Ti6Al4V alloy formed in various types of phosphate electrolyte solutions

  • 期刊论文

  • 发表日期：

    2025年12月22日

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  • Qian Xiang,
  • Xuejun Cui,
  • Yuming Qi,
  • Xingyou Chen,
  • Jun Liang,
  • Deen Sun

摘要

Phosphate-based electrolytes are among the most efficient media for microarc oxidation (MAO), as they enable rapid coating growth at low breakdown voltages and short formation times. In this study, MAO coatings were fabricated on Ti6Al4V titanium alloy using four different phosphate-based electrolytes, including several common and representative orthophosphates and polyphosphates. The aim was to investigate how electrolyte composition influences the coating formation mechanism, microstructure, and functional properties. Discharge characteristics and plasma behaviours during the MAO process were monitored using optical emission spectrometry and real-time surface state analysis. All resulting coatings exhibited n-type semiconducting behaviour and were primarily composed of TiO2, with rutile identified as the dominant crystalline phase. Coating growth occurred predominantly in the outward direction, driven by the combined effects of substrate oxidation and deposition of phosphate compounds. Photocatalytic degradation tests using methyl orange showed that all coatings achieved degradation efficiencies exceeding 40% within 6 h. Among the tested electrolytes, coatings formed in Na5P3O10 solutions demonstrated the highest corrosion and wear resistance, with a corrosion current density of 2.28 × 10–9 A/cm2 and a wear rate of 4.10 × 10⁻3 mm3/(N·m). The results indicate that polyphosphates increase breakdown voltage and accelerate coating growth, making them suitable for short-duration processes. In contrast, orthophosphates reduce breakdown voltage, promoting sustained densification over longer treatment periods. Furthermore, phosphates with a molecular weight of three or more emerge as optimal electrolytes for fabricating functional MAO coatings on Ti6Al4V alloys.