Abstract

Self-replenishable ways of applying solid lubrication in tribological systems are limited to the use of sintered self-lubricating composites. These are obtained by mixing solid lubricants with metallic powders or by the in situ precipitation of the lubricating phase. Both techniques can produce self-lubricating composites able to promote low friction coefficients in dry sliding conditions. However, the combination of solid lubricant and matrix is limited by the thermodynamic interactions during sintering. Filling the pores of sintered parts with solid lubricants by vacuum impregnation is a versatile way to promote solid lubrication, allowing any combination of solid lubricant and matrix to be used, avoiding deleterious phases and other sintering problems typical in sintered self-lubricating composites. In this work, low alloy sintered steel was produced by mixing Astaloy CRL powders with 0.6 wt% C, the sintered specimens were impregnated with graphite (1.10 mu m), and the durability and wear rates of the resulting composites were studied using ball-on-flat reciprocating tests. The results show that the impregnation technique is able to fill the surface pores with graphite, producing friction coefficients down to 0.06 in dry-sliding conditions and wear rates ranging from 10-4 to 10-7 (mm3/N-m). The main wear mechanism of the impregnated specimens was plastic deformation on the surface, which causes sealing of pores, while the wear of the counter-bodies was mainly abrasive. The durability of the lubricity regime is directly proportional to the amount of lubricant available as pores get sealed by the sliding action of the counter-body, so is proportional to the porosity.