Improvement of the corrosion resistance of C/Al-composites by diamond-like carbon coatings

Abstract

Because of the extreme sensitivity of carbon fiber reinforced aluminum (C/Al-compound) to electrochemical corrosion suitable protection methods are necessary. Improved corrosion resistance can be achieved by applying appropriate coatings. Diamond-like carbon (DLC) coatings provide properties, which make them interesting materials for external corrosion protection of MMCs (Metal Matrix Composites). The hydrogenated, amorphous carbon coatings not only reveal outstanding wear resistance and good adherence to the heterogeneous MMC-substrate, but also results in an improvement of corrosion resistance. The lightweight and dense DLC-coating covers up the underlying substrate and separates the MMC from the attacking electrolyte. The electrochemical corrosion behavior of uncoated and DLC-coated C/Al-composites is tested in 3.5 wt.% NaCl solution by using potentiodynamic polarization with low scanning rates tests. It has been found that the pitting potential is shifted significantly in the anodic direction and the corrosion current density is much lower due to the presence of the sealing DLC-coating. Additionally, tranmission electron microscope (TEM) and scanning electron microscopy (SEM) studies were performed in order to characterize the fiber-matrix interface and the corrosion mechanisms of uncoated and DLC-coated MMCs.