New coating with superior corrosion and wear performances: Parylene C/CrN duplex coating

Abstract

Growth defects such as pores during preparation restrict the service life and wide applications of CrN coating. To improve the corrosion and tribological behaviors of CrN coatings, in this work, the parylene C (PC)/CrN duplex coatings with different CrN layer thicknesses were fabricated, combining chemical vapor deposition and physical vapor deposition technologies. The surface morphologies and chemical bonds of as-deposited coatings were investigated by scanning electron microscopy and x-ray photoelectron spectroscopy, respectively. The corrosion and wear behaviors of the CrN coatings without and with PC layers in the seawater environment were evaluated using an electrochemical workstation and a tribometer, respectively. The results showed that the surface of the PC film was relatively compact, which was well bounded to the CrN layer. The corrosion current density of the PC/CrN duplex coating is low to 10−9 A/cm2, which is reduced by one order of magnitude compared to the single CrN coating. As the thickness of the CrN layer increases, the corrosion potential of the PC/CrN duplex coating decreases and the corrosion current density slightly increases, which may be ascribed to the increased defects of the CrN layer, which debased the corrosion resistance. Furthermore, the steady friction coefficients of PC/CrN duplex coatings are all below 0.05, which are significantly lower compared to the single CrN coatings. The lowest wear rate of the PC/CrN duplex coating is approximately 1.31 × 10−6 mm3/N m, presenting excellent wear resistance. Compared to the single CrN coating, the dense PC film can not only seal the pores and other defects on the CrN surface, but also prevent the permeation and penetration of corrosive seawater inside the coating, which contributes to the superior corrosion resistance of the PC/CrN duplex coating. The low friction and high wear resistance of the PC/CrN duplex coating could be ascribed to the self-lubricating property, the PC film, and its good protective performance as a surface layer, as well as the generation of CaCO3 and Mg(OH)2 lubrication components during the wear process. In summary, the PC films can remarkably improve the corrosion and tribological performance of the CrN coating. The excellent corrosion resistance and wear resistance of the PC/CrN duplex coating make it a good candidate material for applications in marine environments.