Most PVD coatings are thin, hard refractory nitrides (e.g., CrN, TiN). These materials are naturally chemically inert and resistant to corrosion, which is why PVD coatings are often claimed to be corrosion resistant. However, most of the commercially available PVD coatings are being deposited at less than 3 microns (μm), which is relatively thin for the purpose of corrosion protection. Moreover, a typical PVD coating contain intrinsic defects (such as pinholes and craters) due to the nature of the deposition process. The thin PVD layer with these defects can expose the substrate, leaving it vulnerable to corrosion.