The aim of the current study was to design and investigate the tribological behaviour of NiAl-Cr 2 O 3 -Ag-CNT-WS 2 adaptive self-lubricating coating. For this purpose, feedstock powders with various compositions were prepared by spray drying technique and then plasma sprayed onto carbon steel substrates. The microstructures and worn surfaces of the coating were examined by SEM, EDS and Raman spectroscopy. The tribological properties of the coatings were tested by a high-temperature tribometer in a dry environment from room temperature to high temperature and in a natural humid environment. Preliminary results showed that a new adaptive coating with NiAl-Cr 2 O 3 -Ag-CNT-WS 2 components for humid, dry and mid temperature applications was successfully designed. Coating whose additives were all nano-sized, compared to the coating that only CNTs were nano-sized, possessed a lower and more stable friction coefficient. It was found that the specimen containing 7 vol. % Ag, 7 vol. % CNT and 7 vol. % WS 2 had the best frictional performance. The average room temperature friction coefficient of this coating was 0.36 in humid atmosphere, 0.32 in dry atmosphere, and 0.3, 0.28, 0.26 and 0.28 at 100, 200, 300 and 400 o C, respectively. This coating was selected as the coating with the optimized composition. The results also revealed that lubrication mechanism at humid condition was the formation of a lubricious graphite layer on the coating worn surface. Lowering friction coefficient of the coating at dry condition was due to formation of a layer containing a mixture of tungsten sulphide and graphite on the wear surface, and the development of a glaze layer made of a mixture of silver, nickel oxide and chromium oxide along with carbon nanotubes that resulted in the self-lubrication behaviour at moderate temperatures. The results of this study suggested that the optimized coating described could be valuable for sliding contact components in advanced heat and high temperature engines. Keywords: Nanocomposite coating; Solid lubricants; Self-lubrication, Adaptive coatings, High temperature wear; Coefficient of friction
