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This study summarizes the development, characterization, and application of nanocomposite tribological coatings on rolling element bearings. Nanocomposite coatings consisting of nanocrystalline metal carbides embedded in amorphous hydrocarbon or carbon matrices (MC/aC:H or MC/aC) have been used to increase the fatigue life under boundary layer lubrication, provide debris tolerance, eliminate false brinelling, increase the operational speed, decrease the friction, and provide oil-out protection to rolling element bearings. MC/aC:H coatings are applied by magnetron sputtering at substrate temperature less than 180 °C, have small friction coefficients, high fracture strength, and can have hardness and modulus values twice and half that of carburized steel, respectively.

Aluminum nitride and microalloy carbonitrides have been identified as microstructural features that degrade the ductile fracture resistance of tempered martensitic microstructures. A thermal/thermomechanical process has been developed to optimize the toughness of high-strength steels containing any species of grain-refining precipitate that is soluble in austenite, and the process is particularly effective at improving the impact toughness of aluminum-killed EAF steels. The process affects the mode of unstable fracture in tempered martensitic microstructures, such that at constant strength and austenite grain size, substantial improvements are realized in both longitudinal and transverse toughness over relatively broad ranges of sulfur content and tempering temperature.