Friction and wear behaviour of steam-oxidized sintered iron components coated with manganese phosphate

Abstract

Steam oxidation is an important industrial procedure for changing tribological properties, sealing porosity and improving aesthetics in sintered iron components. Manganese phosphate coatings are believed to have intrinsic lubricant properties and very low friction coefficients. In this work, after steam oxidation, sintered iron components were coated with manganese phosphate and their tribological behaviour was investigated. Components with two nominal film thicknesses were compared, either coated or uncoated with manganese phosphate. Their abrasion resistance was evaluated using micro abrasion wear tests. Reciprocating wear tests were used to study their sliding wear resistance. It was observed that phosphating of the oxidized samples resulted in an increase of the wear rate in both tests. Phosphating promoted a reduction of the oxide film thickness, probably due to the chemical conversion reaction with the oxide substrate. The reduction of wear resistance due to phosphating was associated with a reduction of oxide film thickness.