Preparation of Al2O3/DLC/Au/MoS2 chameleon coatings for space and ambient environments

We have investigated the tribological properties of nanocomposite "chameleon" coatings, which adapt their low friction behavior with the surrounding environmental humidity and temperature. The material system of interest included alumina (Al2O3) in an An matrix with diamondlike carbon (DLC) and MoS2 nanoparticle inclusions. The coating design included formation of nanocrystalline hard oxide particles for wear resistance, embedding them into an amorphous matrix for toughness enhancement, and inclusion of nanocrystalline and/or amorphous solid lubricants for friction adaptation to different environments. Chemical analysis was used to ascertain a correlation between chemical bonding of species and frictional properties. Friction measurements were studied in cycling between humid air and dry nitrogen conditions at room temperature and during heating in air to 500 degrees C. It was observed that both graphitic carbon and MoS2 worked together to give low friction in variable humidity environment, while Au was valuable for a low friction at elevated temperatures. Friction coefficients were found to be 0.02-0.03 in dry nitrogen, 0.1-0.15 in humid air, and 0.1 in air at 500 degrees C. Thus the tribological property results have shown that the system provides "chameleon" type adaptation behavior in different environments relevant for aerospace systems. (c) 2006 Published by Elsevier B.V