Pulse width effects on microstructure and electrochemical properties of DLC coatings deposited on high-strength Al alloy

Abstract This study utilized a cage-like hollow discharge plasma-enhanced chemical vapor deposition method to make diamond-like carbon (DLC) films on a 2024 aluminum alloy. DLC films were synthesized with different pulse widths. The microstructural and mechanical properties of the films were assessed using various techniques. The corrosion properties of the films were investigated in a 3.5 wt. % NaCl solution. The investigation indicated that when the pulse width rose the thickness of the DLC coatings increased owing to the enhanced plasma density and deposition rate. Raman spectroscopy detected a rise in the ID/IG ratio from 1.28 to 1.32, suggesting alterations in the structural integrity of the coatings. Furthermore, the hardness and Young's modulus of the DLC coatings decreased from 14.5 to 13.31 GPa and 124 to 115 GPa, respectively, with increasing pulse widths from 10 to 20 μs. Electrochemical tests revealed a positive change in the corrosion potential from -631 to -565 mVAg/AgCl and a decrease in the corrosion current density from 1.59×10-6 to 1.23×10-7 A/cm² as the pulse width increased from 10 to 20 μs. This behavior can be attributed to the higher thickness of the DLC film, which effectively reduces the presence of pores and inhibits corrosive species from attacking the bare alloy. In addition, thermodynamic corrosion parameters were calculated.