Investigation of erosion-corrosion mechanisms of UNS S31603 using FIB and TEM

Accelerated wear due to synergy during erosion-corrosion of UNS S31603 is extremely complex. It is this reason that current modelling approaches fail to accurately model the physical mechanisms in this wear process. The objective of this work was to perform FIB and TEM analysis on UNS S31603 to investigate the subsurface deformation mechanisms and microstructural changes in the material during erosion-corrosion. FIB investigation revealed a decrease in grain size at the surface and a change in grain orientation towards the impact direction. Networks of cracks were observed near the surface which is believed to be caused by work hardening of the material which increased the material susceptibility to fatigue cracking. Folding of lips is also proposed as an important mechanism for subsurface wear. The large amount of strain imposed on the material also induced martensitic phase transformation. Fragmented erodent particles and oxide film were found embedded into the material which caused formation stress concentrated regions in the material and contributed to crack initiation. A composite structure is formed consisting silicon oxide sand particles and chromium oxide film along with the martensitic phase transformed metal. The corrosive environment is also believed to have played a significant role in the initiation and propagation of cracks. Crack initiation and propagation due to the mechanical and electrochemical processes enhances the material mass loss as the crack networks coalesce and subsequently cause material spalling. Physical models are developed based on these observations to explain the microstructural changes and synergistic mechanisms.