Direct observation of frictional seizure of mild steel sliding on aluminum by X-ray imaging. Part I: Methods

Many of the mechanical or metallurgical failures originate from subsurface cracks or changes in microstructure of the materials. It would be quite informative to material scientists to view the changes below the surface while testing to get a direct evidence of the mechanisms claimed to be governing a particular process like dislocation movement/grain boundary sliding, crack opening displacement, wear, stress concentration etc. In this work, we have used an X-ray microscope for in-situ observation of interfacial features during the friction and wear testing of mild steel specimens sliding against Al 6061 disk. This technique enables the observation of interfacial features of the hidden contact. Multiple tests were conducted at different sliding speeds of 2, 4 and 5 m/s. The images obtained during the tests indicated the presence of various sub surface processes such as adhesive transfer, stress fields, island formation and roughening. Wear was also found to be concentrated over a certain specific area during the initial part of the test but later the contact developed into a conformal contact following a lumpy transfer of material.