Lubrificação sólida em meio fluido

Abstract

In order to reduce friction and wear in tribological pairs, the insertion of lubricant between the surfaces in contact separates them by a lubricant film. In most tribological applications, liquid lubricants or grease are used to combat friction and wear. But when service conditions become very severe, solid lubricants may be the only choice to control friction and wear. A combination of solid and liquid lubrication is also feasible and may have a beneficial synergistic effect on the friction and wear performance of sliding surfaces. It occurs particularly in the boundary and elasto-hydrodynamic regime of lubrication. With advent of the powder metallurgy technique, the production of new materials having solid lubricants particles embedded in the metallic matrix became feasible. This work aims to study the combined effect of solid lubrication (sintered composites which contains particles of solid lubricant dispersed in a metallic matrix, by a basic mixing process), with the presence of a liquid lubricant in cooperative lubrication regime in reciprocating sliding wear configuration. A significant reduction, when compared with the addition of liquid lubricant alone, in friction coefficient (25%) was produced by the simultaneous utilization of solid and liquid lubricants, suggesting the existence of a beneficial synergy between the liquid and solid lubricants. This combined action increased significantly the durability of the lubricious regime (3 orders of magnitude), reduced the friction coefficient (about 4x) and the wear rate by 50%. Additionally, the use of triboscopy technique enabled (in an original form) to verify a significant increase in the friction coefficient at the wear marks of a ferrite perlite alloys. This difference between the friction coefficient according to the position was discussed in terms of debris accumulation and a change in lubrication regime, both associated with the reciprocating motion dynamics having been assigned to the first a preponderant role.