A comparative investigation of the friction and wear behavior of polyimide composites under dry sliding and water-lubricated condition

The friction and wear behavior of high performance polyimide (PI) and its composites reinforced with short cut carbon fiber and solid lubricants such as graphite, MoS2 and polytetrafluoroethylene (PTFE) was comparatively evaluated under dry sliding and water-lubricated condition, aiming at selecting matching materials for the pumps of pure water power transmission. The wear mechanisms of the composites under the two different sliding conditions were also comparatively discussed, based on scanning electron microscopic examination of the worn composite and steel counterpart surfaces. As the results, the incorporation of solid lubricants and carbon fiber in PI contributed to improve the friction and wear behavior considerably. PI-based composites sliding against stainless steel register lower friction coefficients and wear rates under water-lubricated condition than under dry sliding. The difference in the-wear rates of the composites becomes margined under water lubrication, owing to the boundary lubrication effect of the water absorption layer, though the transfer of PI and its composites was considerably hindered in this case. PI and its composites are characterized by plastic deformation, micro cracking, and spalling under both dry- and water-lubricated sliding. Such plastic deformation, micro cracking, and spalling is significantly abated under water-lubricated condition. This accounted for the better friction and wear behavior of the composites under water-lubricated condition. (C) 2003 Elsevier Science B.V. All rights reserved.