Corrosion rate significantly increased as the grain size increased. This is due to
smaller grain size have higher density of nucleation sites for passive
film, which leads to a higher fraction of passive layer, and thus a
lower passive current density. Dense structure can effectively prevent
seawater permeate into coating, enhancing the corrosion resistance
of coating. What is more, the defect can accelerate the corrosion
speed [46]. The distinct defect such as pin holes are not detected
inside the as-fabricated coatings,
the microcracks would grow under cyclic stress in combination with the erosion of water molecules,
resulting in delaminations or spallations around these weak points.
When the flow rates further increase, the corrosion current densities
show an ascending trend to 30 sccm, where the corrosion current
density reaches at about 8.31 107 A/cm2
. In addition, there is a passivation phenomenon when the polarization potential increases
from 0.2 to 0.2 V, which illustrates that the passivation layer is
formed on the surface of the coatings, and then prevents the
substrate exposure to surrounding environment for a short time.
Thus, the CrCN coatings exhibit good corrosion resistance (Table 4).
Corrosion rate significantly increased as the grain size increased. This is due tosmaller grain size have higher density of nucleation sites for passivefilm, which leads to a higher fraction of passive layer, and thus alower passive current density. Dense structure can effectively preventseawater permeate into coating, enhancing the corrosion resistanceof coating. What is more, the defect can accelerate the corrosionspeed [46]. The distinct defect such as pin holes are not detectedinside the as-fabricated coatings, the microcracks would grow under cyclic stress in combination with the erosion of water molecules,resulting in delaminations or spallations around these weak points.When the flow rates further increase, the corrosion current densitiesshow an ascending trend to 30 sccm, where the corrosion currentdensity reaches at about 8.31 107 A/cm2. In addition, there is a passivation phenomenon when the polarization potential increasesfrom 0.2 to 0.2 V, which illustrates that the passivation layer isformed on the surface of the coatings, and then prevents thesubstrate exposure to surrounding environment for a short time.Thus, the CrCN coatings exhibit good corrosion resistance (Table 4).
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