The surface oxidation and subsurface microstructure evolution of Alloy 690TT can occur during partial slip fretting corrosion in high-temperature pure water.Detailed characterization methods such as laser scanning confocal microscopy,scanning electron microscopy,electron probe micro-analyzer,and transmission electron microscopy were used to reveal the related mechanism.The results showed that Cr2O3 oxides together with a small number of spinel oxides were formed in sticking region since a small quantity of high-temperature water could pass through the gaps between the asperities to oxidize the materials.Widespread distribution of oxides in microslip region consisted of (Ni,Fe)Cr2O4,because Ni2+ and Fe2+ ions could react with Cr2O3 to generate a small amount of non-stoichiometric spinel oxides.The oxides around micropitting in microslip region consisted of double-layer structure.The outermost layer contained (Fe,Cr)-rich oxides due to the effect of fretting leading to mechanical mixing between Cr2O3 and (Ni,Fe)(Fe,Cr)2O4.The inner layer consisted of (Fe,Ni)-rich oxides owing to the consumption of Cr2O3 by the reaction with Ni2+ and Fe2+ ions.The reciprocating motion of oxide particles in microslip region resulted in the stress-strain supporting the recrystallization for the formation and development of a tribologically transformed structure in subsurface and plowing effect by fretting in surface.