The tribological performance at elevated temperatures of MoNbN-Ag coatings

Sliding components, such as reciprocating and rolling contact bearings of aero engines, are rapidly heated by viscous friction when aerospace vehicles are working at high Mach number. Repeated friction and wear at high temperatures can easily cause deformation or even breakage of the sliding parts, thereby reducing the service life of the materials. Therefore, the new generation of materials for components requires not only excellent mechanical properties, but also reliable tribological properties at elevated temperatures. In this work, based on the tough yet hard ternary MoNbN solid solution, we designed and synthesized solute structure MoNbAgN and nanocomposite MoNbN/Ag coatings. These Ag-containing coatings exhibit a lower friction coefficient than the pure MoNbN coating at temperatures between room temperature (RT) and 800 degrees C. The nanocomposite MoNbN/Ag coating presents the lowest friction coefficient in the middle-low temperature range (RT-450 degrees C), while the solute structure MoNbAgN coating exhibits the best friction coefficient in the middle-high temperature range (450-700 degrees C). In the high temperature range (700 degrees C and above), the solute structure MoNbAgN and nanocomposite MoNbN/Ag coatings have similar friction coefficients. The different tribological behaviors of these coatings can be ascribed to the different lubrication products and wear mechanisms at different temperature ranges. The manufacture of Ag-containing transition metal nitride coatings represents a new approach towards the realization of low friction at elevated temperatures.