Adaptive nanocomposite coatings with a titanium nitride diffusion barrier mask for high-temperature tribological applications

Adaptive nanocomposite coatings that demonstrate low friction throughout broad ranges of temperature, wear, humidity and other environments are currently in development. One effective temperature adaptation mechanism at temperatures ≤ 500 °C is diffusion of noble metal to the coating surface, providing a low shear strength interface at the friction contact supported by a hard surface underneath. To prolong the wear lifetime of chameleon coatings relying upon this mechanism for low friction, a coating architecture incorporating a diffusion barrier mask to inhibit noble metal diffusion was employed. The diffusion barrier-capped coating provided lubrication at 500 °C over ten times longer than the monolithic yttria-stabilized zirconia–silver–molybdenum coating of the same thickness without failure. Characterization of coatings after heating with surface analysis and microscopy techniques revealed the mechanism for increased coating life, and allowed for measurement of silver self-diffusion parameters in the adaptive nanocomposite material.