Polydopamine + SiO2 nanoparticle underlayer for improving DLC coating adhesion and durability

A diamond-like carbon (DLC) coating was deposited using a plasma-enhanced chemical vapor deposition (PECVD) method on a polydopamine (PDA) and SiO2 nanoparticle (NP) composite underlayer (PDA + SiO2) to improve its resistance to crack propagation and coating delamination, especially under cyclic loading conditions. Scratch and linear reciprocating wear tests were conducted to identify the critical loads and wear mechanisms of the coating. The PDA + SiO2/DLC coating was also compared with DLC coatings without an underlayer, with a PDA underlayer, and with a trimethylsilane [(CH3)3SiH] (TMS) underlayer. The PDA + SiO2/DLC coating significantly increased the critical loads for initial crack propagation, initial delamination, and global delamination. Linear reciprocating wear tests revealed that the PDA + SiO2/DLC coating had a 2.5 times reduction in the wear track cross-sectional area, and the average dimension of the cracks was 40 times smaller than those of the TMS/DLC coating. Therefore, the PDA + SiO2/DLC was superior in preventing coating crack propagation and delamination compared to the TMS/DLC coating.