Microstructural characteristics of Alloy 690TT subjected to fretting corrosion in high temperature water

Microstructural characteristics of Alloy 690TT subjected to fretting corrosion in high temperature water were investigated. The results indicated that there were oxide, tribologically transformed structure (TTS) and deformation layers in worn subsurface. Oxide layer had a multilayered structure: the outer part consisted of Fe rich spinel oxides and tribolayer which was composed of Fe3O4 and Cr2O3; the inner part contained local amorphous Cr-rich oxides. TTs layer consisted of equiaxed nanograins which formed due to dynamic recrystallization of deformed structure. Internal oxidation occurred within TTS layer because the nanograins provided the short-circuits for oxygen diffusion, resulting in the ellipsoid and stripe-like Cr2O3.