A broad range of environmental conditions are associated with hypersonic flight and other advanced aerospace applications.Presently, no lubricant is available to provide low friction from takeoff to landing in high-performance flights of this nature, as opposite extremes of humidity, loading and temperature are reached over a single flight cycle. Adaptive nanocomposites, also known as “chameleon coatings”, are a class of materials that automatically adjust surface composition and structure to minimize friction as the ambient environment changes, and may provide the properties necessary to reduce downtime for aerospace systems subjected to repeated atmospheric cycling. Friction coefficients of YSZ–Ag–Mo adaptive nanocomposite coatings with different MoS2 additions were measured from 25 to 700°C, and correlated to the composition and microstructural evolution of the coatings during testing. Adding 8% MoS2 to the YSZ–Ag–Mo coatings resulted in a decrease in the friction coefficient from 0.4 to 0.2 from 25 to 700°C. Lower friction in the 25–300°C temperature range resulted from MoS2 lubrication. At higher temperatures the MoS2 additions did not directly provide lubrication, but rather promoted the formation of lubricious silver molybdate phases at the coating surface.
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