EBSD, SEM and FIB characterisation of subsurface deformation during tribocorrosion of stainless steel in sulphuric acid

The tribocorrosion behaviour of a 304L stainless steel/alumina contact was investigated in sulphuric acid at two imposed potentials (cathodic and passive). The metal deformation below the surface was investigated by analyzing cross sections using secondary electron microscopy (SEM) and electron back scatter diffraction (EBSD). Cross sections were also prepared using focussed ion beam (FIB) and analyzed by in situ SEM. AES depth profiling was used to analyze surface composition. Metal subsurface deformation resulted in the build up of a deformed layer of approximately 20 μm thickness in the near surface zone within the wear track. This layer exhibited a deformation gradient with high deformation close to the surface resulting in grain refinement down to 10 nm. The applied potential influenced the deformation: at passive applied potential more strain was accumulated below the surface resulting in more pronounced grain refinement and higher density of defects. Using AES analysis no alumina transfer from the counter body or any significant burying of oxide below the surface could be detected.