The Roles of Molybdenum and Ion-Mixing in Producing Friction-Reducing Films

Abstract

The roles of molybdenum and ion-mixing on the tribological characteristics of friction-reducing films have been investigated in a laboratory test. The effect of an electric field on the friction stability and the localization of phosphate formation were also studied. Electro-coated iron-molybdenum piston ring specimens demonstrated better friction stability and lower friction coefficients than specimens of uncoated iron-molybdenum. This is believed to be due to the formation of localized phosphate films in molybdenum-poor regions. In addition, based on results for samples with different degrees of ion-mixing, ion-mixed Fe/Mo ring specimens further reduced slidring friction and enhanced friction stability. Fewer stick-slip or wear-induced vibrations occurred for the sample with increased ion-mixing. In addition, for this same sample, no significant stick-slip or wear-induced vibrations were observed during a continuous lubricated sliding process of 400 hours. Surface analyses indicate that increased ion-mixing promotes a broad Mo/Fe interface and increases phosphate penetration. These results suggest that electro-coated and ion-mixed Fe/Mo films both have potential for use in reducing sliding friction.