Frictional seizure of aluminium observed by X-ray imaging

Abstract

Friction and wear of non-ferrous metals and coatings are of considerable interest in the light of use of the above in tribo-contacts. As most of the mechanisms governing the seizure of materials are concentrated at the center of the contact and are hidden, it is difficult to observe any precipitate changes in the behavior of such materials using conventional tools. In this work, we have used an X-ray microscope for in-situ observation of frictional seizure, wear and interfacial features during the testing of aluminium (AA1100) specimens sliding against Al 6061 disk. This technique enables the observation of interfacial features of the hidden contact despite the small density differences that exist between the sliding pair of materials. Seizure tests were conducted at different sliding speeds of 2 and 4 m/s. Aluminium was found to undergo incipient melting during sliding at a sliding speed of 2 m/s whereas the specimen tested at 4 m/s was found to undergo a severe plastic distortion thus restricting further testing of the same. Frictional heating of concentrated spots resulted in melting wear and diffusion assisted bonding of surface layers. This was later found to develop into a conformal contact following a lumpy transfer of material. The mechanisms of seizure and wear were affected by the sliding speeds during testing. At lower sliding speed (2 m/s) the transfer and bonding of deposits occurred due to direct contact of nascent sliding surfaces.