Crack-bridging Bonding in Trivalent Chromium Composite Coatings on Pure Aluminum Using Carbon Nanotubes for Wear Resistance

摘要

The trivalent chromium composite coatings with multiwall carbon nanotubes (MWCNTs) werefabricated by the direct current deposition under an ultrasonic agitation on the pure aluminum substrateusing a zincate interlayer. Compared with the trivalent chromium coatings, the chromium compositecoatings about 35 m thick with MWCNTs have the similar amorphous microstructure with a limitedcrystallization. The horizontal stymie of carbon nanotubes between the chromium grains was mainlylocated in the chromium composite coatings. A slightly increased microhardness to HV1 N 9.2-9.8 GPawas obtained from HV1 N 8.0-8.3 GPa of the pure chromium coatings. During the tribological test on aball-on-disc tribometer against an Si3N4 ceramic courterface under a normal load of 0.5-2 N, thesimilar friction coefficient of the two trivalent chromium coatings changed in 0.60-0.47, which wasdependent on the applied normal load. However, the significant increase in wear resistance of thechromium composite coatings with MWCNTs, relative to that of the pure chromium coatings, wasfound with the specific wear rate decreased by about 30-40 % under the applied normal load. A crack- bridging bonding model was proposed to explore the improvement mechanism in wear resistance bythe carbon nanotubes as reinforced nanometer fiber in the trivalent chromium composite coatings.