Electrochemical behavior of the double-layer diamond-like carbon/plasma electrolytic oxidation on AZ31 alloy: A comparison of different PEO interlayers

In the present study, a double-layer diamond-like carbon (DLC)/plasma electrolytic oxidation (PEO) coating was developed on the AZ31 substrate and its electrochemical behavior was studied. In this regard, after fabrication of PEO coatings using two different electrolytes (silicate (PEO-Si) and phosphate (PEO-Ph) compounds), DLC thin films were synthesized on the substrates using the radio frequency plasma-enhanced chemical vapor deposition (RFPECVD) method. Results showed the successful formation of thin and crack-free DLC layer with the thickness of about 1 mu m on the middle PEO layers. However, the structure and chemical stability of the final DLC layer was dependent on the PEO composition. Moreover, the electrochemical studies in buffer phosphate saline (PBS) at the normal body temperature (37 +/- 0.5 degrees C) showed that while both PEO-Ph and PEO-Si layers significantly decreased the corrosion rate of substrate, PEO-Ph revealed better electrochemical performance. On the other hand, DLC/PEO-Si was more effective than DLC/PEO-Ph to decrease the corrosion rate of substrates owing to the greater bonding of DLC coating on PEO-Si layer. In summary, crack-free DLC/PEO coatings could be a promising candidate to prevent from the high corrosion rate of magnesium alloys, making it appropriate for biomedical applications.