Fretting-Corrosion Behavior of Stellite 6 Overlay Welded on 304 Stainless Steel in Simulated PWR Water Environment

The fretting-corrosion behavior of a Stellite 6 cobalt-based overlay welded to 304 stainless steel was investigated in simulated high-temperature, high-pressure PWR water. Three material pairings were examined: Stellite 6/Stellite 6 (C-C), Stellite 6/304 stainless steel (C-S), and 304 stainless steel/304 stainless steel (S-S). Wear behavior was evaluated in terms of mass loss, surface morphology, surface chemistry, friction evolution, and subsurface deformation. The results show that material pairing strongly affects friction stability and damage evolution during fretting corrosion. The C-C contact exhibited a relatively stable coefficient of friction and continuous wear morphology, with damage dominated by plastic deformation. In contrast, the C-S and S-S contacts exhibited stronger wear–corrosion interaction, characterized by debris accumulation, oxide film instability, and fluctuating friction behavior. Despite the same oxide species being observed in different contact pairs, their distribution and stability varied greatly, which resulted in different modes of damage. EBSD analysis showed that fretting energy in the C-C contact was mainly accommodated by plastic strain in the near-surface region, whereas deformation in the C-S and S-S contacts was more localized and discontinuous. These results indicate that oxide film stability and subsurface strain distribution jointly control friction behavior and fretting-corrosion damage under different material pairings.