Abstract
The tribocorrosion behavior of Inconel 690TT in NaOH (pH = 9.8) solution at different normal forces was investigated by an electrochemical method. The results indicated that normal force had a great effect on the tribocorrosion behavior and mechanism. When normal force increased from 15 to 30 N, fretting regime was in gross slip regime (GSR), and wear volume gradually increased. When normal force further increased to 45 N, wear volume significantly decreased due to the fretting regime changing from GSR to partial slip regime (PSR). When fretting ran in GSR, the corrosion resistance decreased with the negative shift of open circuit potential (OCP). However, when the fretting regime changed to PSR, the corrosion reaction significantly decreased due to the adhesive wear. Fretting wear broke the passive film at the contacting surface, which caused the worn surface to be more active and prone to corrosion. However, the broken passive film was quickly repaired in subsequent oxidation. The break and repair of passive film strongly depended on normal force. In GSR, the increase in normal force aggravated the break of passive film. In PSR, the passive film was not easy to break with a further increase of normal force.
Highlights
Inconel 690TT has been widely used as a structural material for steam generator (SG) tubes in nuclear power plants due to the fact of its outstanding mechanical strength and corrosion resistance [1]
When the normal force increased from 15 to 30 N, the fretting regime was mainly a gross slip regime; when the normal force further increased to 45 N, the fretting regime changed to a partial slip regime
When the normal force further increased to 45 N, the wear volume decreased significantly due to the change in the fretting regime from a gross slip regime to a partial slip regime; The electrochemical behavior on the worn surface strongly depended on the fretting wear mechanism
Summary
Inconel 690TT (thermally treated) has been widely used as a structural material for steam generator (SG) tubes in nuclear power plants due to the fact of its outstanding mechanical strength and corrosion resistance [1]. Fretting can occur in the SG tubes, which is an important issue due to the flow-induced vibration in the pressurized water reactor (PWR) [2]. Due to the pH value of the secondary side water in the PWR being usually controlled at 9.0~10.0 [3,4], the solution can act as an electrolyte for the electrochemical corrosion of the SG tube. The mechanical removal of passive oxide film accelerated the material’s deterioration [5]. Fretting corrosion of SG tubes is a combination of two simultaneous interfacial processes: One is the mechanical removal of material in the form of wear debris. Many investigations on fretting corrosion of Inconel 690TT have been carried out with the fretting parameters including displacement amplitude [6,7], normal force [6,7,8], cycle number [9,10], temperature [3,11,12,13], and microstructure evolution [14,15,16,17,18]
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