Surface Oxidation and Subsurface Microstructure Evolution of Alloy 690TT Induced by Partial Slip Fretting Corrosion in High-Temperature Pure Water

Long Xin¹，Yongming Han¹，Ligong Ling^1,2，Yonghao Lu¹，Tetsuo Shoji^1,3

1. National Center for Materials Service Safety,University of Science and Technology Beijing2. Nuclear and Radiation Safety Center3. Frontier Research Initiative,New Industry Creation Hatchery Center,Tohoku University

摘 要：The surface oxidation and subsurface microstructure evolution of Alloy 690 TT 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 Cr₂ O₃ 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）Cr₂ O₄,because Ni²⁺ and Fe²⁺ ions could react with Cr₂ O₃ 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 Cr₂ O₃ and（Ni,Fe）（Fe,Cr）₂ O_4.The inner layer consisted of（Fe,Ni）-rich oxides owing to the consumption of Cr₂ O₃ 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.

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