Intermediate temperature tribological behavior of carbon nanotube reinforced plasma sprayed aluminum oxide coating

Tribological behavior of plasma sprayed carbon nanotube (CNT) reinforced aluminum oxide (Al(2)O(3)) composite coatings was examined at room temperature, 573 K and 873 K using tungsten carbide (WC) ball-on-disk tribometer. The weight loss due to wear of Al(2)O(3) coating was found to be increasing with the temperature while Al(2)O(3)-CNT coating showed a decreasing trend in the weight loss with the temperature. Relative improvement in the wear resistance of Al(2)O(3)-CNT coating compared to Al(2)O(3) coating was found to be 12% at room temperature which gradually increased to similar to 56% at 573 K and similar to 82% at 873 K. Protective layer as a result of tribo-chemical reaction was observed on the wear track of both of the coatings. The improvement in the wear resistance of Al(2)O(3)-CNT coating was attributed to three phenomena viz. (i) higher hardness at the elevated temperature as compared to Al(2)O(3) coating, (ii) larger area coverage by protective film on the wear surface at the elevated temperature and (iii) CNT bridging between splats. The coefficient of friction (COF) of Al(2)O(3) coating was nearly constant at room and elevated temperature whereas COF for Al(2)O(3)-CNT coating decreased at the elevated temperature (873 K). (C) 2009 Elsevier B.V. All rights reserved