Chiang Mai Journal of Science

Traditional powder metallurgical process is commonly used for producing self-lubricating composites. Solid lubricant dispersion in the steel matrices affects tribological properties by lowering friction coefficient leading to lifetime extension of steel matrix composite parts. Molybdenum disulfide (MoS₂) is one of the most used solid lubricants since its lamellar crystalline structure can form a sliding film adhering to the rubbing surfaces. The sliding film acts as anti-friction or anti-wear layer. Due to such action, MoS₂ is widely used for providing friction reduction in a situation where the use of liquid lubricants is impractical. However, MoS₂ decomposes and reacts with the matrix at high temperatures, usually employed for producing sintered self-lubricating composites. The reaction leads to undesirable products when the powder metallurgical route is used to incorporate MoS₂ into steel matrices. In order to lessen undesirable reaction, the temperature-activated phenomenon, resulting in decrease of lubricating efficiency, it is necessary to find the method for mitigating decomposition and reaction. In this work, tin (Sn) powder was added to the mixtures of 316L stainless steel and MoS2 powders with expectation that sintering enhancement by Sn powder addition would reduce sintering temperatures and thus reduce MoS₂ + 316L reaction. Varied MoS₂ contents (5, 10 and 15 wt. %) were mixed with fixed 4 wt. % Sn and balance 316L stainless steel powder. The green compacts of powder mixtures were sintered at temperatures of 1,150 ºC and 1,200 ºC in hydrogen atmosphere for 45 min. Mechanical properties and dry-sliding wear behavior of the sintered composites were investigated. Liquid phase sintering due to Sn powder addition was observed. However, the energy dispersive spectroscopy (element mapping mode) showed that the reaction between MoS₂ and alloying elements in 316L powder occurred and resulted in sulfide formation. It was found that the amount of added MoS2 had influences on the tensile properties, hardness and sintered density. Although wear resistance and friction coefficient slightly increased according to the MoS₂ content, the added MoS₂ amounts higher than 10 wt.% led to adverse effect.