Effect of lubricants on fretting wear of steel

Abstract

Fretting experiments have been carried out on hard steel under lubricated conditions. The results indicate that strong adhesion, which initiated wear, occurred at the slip region in the contact and weak adhesion occurred at the non-slip region in the initial stage of fretting. The adhesion at the slip region was relieved when wear occurred after a certain number of cycles of fretting and lubricants were fed to the worn region to enable the surfaces to move readily with the fretting motion. The relative amplitude between specimens was small at a high coefficient of friction and large at a low coefficient of friction. Remarkable reductions in friction and wear were observed in lubricants containing 2% zinc dialkyldithiophosphate (ZDDP). Electron probe X-ray microanalysis observations of the effective surface film, formed during fretting in a lubricant containing 2% ZDDP, showed that phosphorus-containing compounds are more readily produced at the surface by fretting than sulphur and zinc-containing compounds. It was concluded that zinc di-n-octyldithiophosphate is the most effective additive for reducing fretting wear from among the range of ZDDP compounds tested. © 1988.