Journal
SURFACE & COATINGS TECHNOLOGY
Volume 342, Issue -, Pages 198-208Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.surfcoat.2018.02.091
Keywords
Plasma electrolytic oxidation; Local over-growth; Interface; Discharge spark; Individual pulse energy
Funding
- NSFC [51571077, 51621091, 51771079]
- National Basic Science Research Program [2012CB933900]
- Aviation Science Foundation of China [20163877014]
- Fundamental Research Funds for the Central Universities [HIT. BRETIII.201202]
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Plasma electrolytic oxidation (PEO) coatings fabricated on 6061 aluminum alloy under different applied voltages (400 V, 500 V and 600 V) were used to investigate the plasma discharge induced 'local over-growth' characteristics across substrate/coating interface. The instant microdischarges across the local plasma channels induce the 'micro molten pool' products and then solidify rapidly to form 'over-growth' oxides region extending into substrate. A thin bonding layer composed of nanocrystalline and amorphous Al2O3 with a constant thickness of similar to 600 nm is always forming on the interface. The intact interface structure of the local over-growth characteristic patterns was presented perfectly by both microdischarge-sculpted substrate side 'pits' and electrochemically detached coating side 'protrusions'. The patterns demonstrate that the over-growth 'pits' and 'protrusions' gradually grow up with increasing applied voltage, which is attributed to the larger discharge channels and molten pools caused by the increased size and intensity of plasma discharges. The speculative 'over-growth' mechanism of discharge event during plasma electrolytic oxidation process is described. This work provides insights to control 'over-growth' characteristics of substrate/coating interface by tailoring electrical parameters or electrolytes composition. And this strategy has a potential application to fabricate micro-nano structure or optimize outstanding performance of PEO coatings.
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