Design of novel nanocomposite nitride coatings for severe tribological applications

Nanocomposite coatings have lately been attracting a lot of attention mainly because of their superior mechanical and tribological properties even under very severe operating conditions (such as high loads, speeds, temperatures, starved or marginal lubrication, etc.). These coatings may consist of multiple crystalline and/or amorphous phases that make them truly composite and hence multi-functional. In this paper, we primarily focus on the chemical and structural design of such coatings for superior friction and wear properties under lubricated sliding conditions that are typical of various engine applications. As an innovative approach for the design of such coatings, we employed a crystal-chemical model that can be very useful for the selection of right kinds of coating ingredients that are essential for their unique structures and superior property and performance characteristics under severe tribological conditions. Novel MoN_x-Cu coatings produced according to this model could provide friction coefficients as low as 0.04 under boundary lubricated sliding regimes and they could not be scuffed or worn through under the heaviest loading conditions of a block-on-ring test machine.