Running-in due to material transfer of lubricated steel/PA46 (aliphatic polyamide) contacts

The running-in of an aliphatic polyamide 46 (PA 46) pin versus a lubricated steel disk was studied by friction and real-time wear measurements with a pin-on-disk tribometer. It was shown that under certain boundary conditions a transfer film forms and significantly reduces friction and wear. In addition, total wear, wear rate, running-in time and coefficient of friction strongly depend on the roughness of the steel disk. In all experiments the system showed a pronounced running-in behavior, characterized by decreasing and, after a certain time, constant coefficient of friction and wear rate. When the roughness of the steel sample was high, abrasion and high friction predominated. For disks with small roughness material transfer became effective and friction and wear decreased accordingly. Material transfer was proven by radioactive labeling of the polymer and detecting its traces on the steel surface. In addition, photoelectron spectroscopy was applied to find fractions of the PA 46 amine groups in the wear track.