Nanocomposite tribological coatings were designed to respond to changing environmental conditions by self-adjustment of their surface properties to maintain good tribological performance in any environment. These smart coatings have been dubbed ‘‘chameleon’’ because, analogous to a chameleon changing its skin color to avoid predators, the coating changes its ‘‘skin’’ chemistry and structure to avoid wear. The concept was originally developed using WC, diamond like carbon, and WS2 material combination for adaptation to a humid/dry environment cycling. In order to address temperature variation, nanocomposite coatings made of yttria-stabilized zirconia ~YSZ in a gold matrix were developed with encapsulated nanosized reservoirs of MoS2 and diamond like carbon ~DLC. Coatings were produced using a combination of laser ablation and magnetron sputtering. They were characterized by x-ray photoelectron spectroscopy, x-ray diffraction, transmission electron microscopy, x-ray energy dispersive spectroscopy, and micro-Raman spectroscopy. Results were correlated with mechanical and tribological characterization. Coating hardness was evaluated using nanoin dentation, while coating adhesion and toughness were estimated using scratch and Vickers indentation tests. Friction and wear endurance measurements of YSZ/Au/MoS2 /DLC coatings against steel and Si3N4 balls were performed at room temperature in controlled humidity air, dry nitrogen, and vacuum environments, as well as at 500 °C in air. Depending on the environment, coating friction surface changed its chemistry and structure between ~ graphitic carbon for sliding in humid air hexagonal MoS2 for sliding in dry N2 and vacuum ~c.o.f. 0.02–0.05!, and ~iii! metallic Au for sliding in air at 500 °C ~c.o.f. 0.10–0.20. The unique coating skin adaptation realized with YSZ/Au/MoS2 /DLC and WC/DLC/WS composites proves a universal applicability of the chameleon design concept. The chameleon coating concept was further developed within the YSZ/Au/MoS2 /DLC material system. This concept combined toughness improvement by nanocry stalline/ amorphous structures with adaptive tribological behavior through designing surface skin chemical and structure response to environment variations. The YSZ/Au base matrix provided excellent mechanical properties for contact load support and also served as an Au reservoir for high temperature lubrication. Encapsulation of amorphous MoS2 and DLC nano reservoirs into this matrix was used for lubrication in dry and humid environments, respectively.
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