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

Because of the extreme sensitivity of carbon fiber reinforced aluminum (C/A l-compound) to electrochemical corrosion suitable protection methods are ne cessary. Improved corrosion resistance can be achieved by applying appropri ate 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 o nly reveal outstanding wear resistance and good adherence to the heterogene ous MMC-substrate, but also results in an improvement of corrosion resistan ce. The Lightweight and dense DLC-coating covers up the underlying substrat e 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 scan ning rates rests. It has been found that the pitting potential is shifted s ignificantly in the anodic direction and the corrosion current density is m uch lower due to the presence of the sealing DLC-coating. Additionally, tra nmission electron microscope (TEM) and scanning electron microscopy (SEM) s tudies were performed in order to characterize the fiber-matrix interface a nd the corrosion mechanisms of uncoated and DLC-coated MMCs. (C) 1999 Elsev ier Science S.A. All rights reserved.