Crack branching behavior and amorphous film formation mechanism during SCC expanding test for multi-layers weld metal of NiCrMoV steels. (April 2022)

• Record Type: Journal Article
• Authors: Chu, Tongjiao; Shao, Chendong; Wang, Yaqi; Ma, Ninshu; Lu, Fenggui
• Is Part Of: Materials & design. Volume 216(2022)
• Publication Date: 2022-04
• Subjects: Stress corrosion cracking -- Crack growth rate -- Amorphous film -- Nanocrystal -- Crack branching; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2022.110520
• Languages: English
• ISSNs: 0264-1275

Abstract

Graphical abstract: Highlights: Crack growth rate in 3.5% NaCl solution was slight slower than in pure water due to crack branching and passivation. Under the invading of Cl - ions in multi-directions and hindering of nanocrystals, crack bifurcated even at lower stress intensity. Amorphous film was discovered to form in crack due to disorder of atom arrangement generated from selective corrosion. Driving force for crack propagation was weakened by compact amorphous film in absence of transporting channel for corrosive ions. Abstract: Multi-layer weld metal of NiCrMoV steels used in nuclear rotor was adopted to perform stress corrosion cracking (SCC) test at 180 ℃, which indicated the crack growth rate in 3.5% NaCl solution was lower than that in pure water. The results obtained from high resolution transmission electron microscopy (HRTEM) analysis revealed that the combined effect of crack branching behavior and amorphous film made contributions to the slower crack growth rate. The aggressive Cl − ions invaded grain in multi-directions that was promoted by dislocation motion, facilitating the main crack to bifurcate. Besides, nanocrystals also enhanced branching behavior by deflecting the crack growth path. An amorphous film forming in crack evolved from the disorder of atom arrangement produced by dislocation accumulation and grew stably with the supplement of carbon atom generated in selective corrosion. The complete amorphous film was absent connected path for migration of aggressive anions, thus weakened the driving force for crack propagation and improved resistance to localized corrosion attack.