Nano Si 3 N 4 composites with improved tribological properties

ABSTRACTNano Si 3 N 4 composites with tailored microstructure were developed using fi ne s-Si 3 N 4 powders. Their wear behaviour was investigated. Whereas pure Si 3 N 4 composites showed improved wear behaviour under dry rolling conditions with slip, TiN-reinforced nano Si 3 N 4 composites generate a self-lubricating behaviour under dry sliding conditions. After chemical treatment with hydrogen sulphide, the friction coeffi cient and wear rate was found to be signifi cantly decreased under dry sliding conditions. Additionally, the new composites possess higher fracture toughness than the pure nano Si 3 N 4 materials. Copyright © 2009 John Wiley & Sons, Ltd.key words: dry wear; silicon nitride; nano; titanium sulphides; self-lubricating behaviour INTRODUCTIONRolling contact ceramic bearings from silicon nitride are able to meet the requirements of higher effi ciency, speed, reliability and accuracy, greater stiffness, longer lifetime, marginal lubrication and better corrosion resistance more easily in comparison to bearings from metal. Under dry sliding con-ditions, their application at high load is limited by high friction. Dry lubrication with solid lubricants was used to solve the wear problems if high specifi c loads or very low hydrodynamic speeds are applied to sliding surfaces. However, dry lubrication is necessary in critical applications if the lubricant must perform over a wide temperature range or under extreme temperature conditions. Dry lubrication is also required in nuclear reactors, in high vacuum applications, in aggressive environments or in applications where contaminations cannot be tolerated. In these applications, diffi culties arise, caused by the insuffi cient distribution of the solid lubricant in the tribological contact, and an expensive enclosure of the bearing becomes necessary. At present, thin MoS