Effects of boundary migration and pinning particles on intergranular oxidation revealed by 2D and 3D analytical electron microscopy

Characterization of the crack initiation and propagation in Alloy 600 with a cold-worked surface

“…However, according to the classic internal oxidation theory [29], to support the occurrence of internal oxidation, an observation of discrete oxide precipitates is prerequisite. Although the intergranular selective oxidation of Cr has been frequently reported [3,6,13,21,24,25,30], there is still no solid evidence to show the existence of discrete oxide precipitates. As a result, the internal oxidation mechanism was modified to be the intergranular selective oxidation mechanism by the subsequent researchers [6,13,21,24,25].…”

“…To date, a number of mechanisms have been proposed to explain the SCC behaviors, including the film rupture mechanism, the hydrogen embrittlement mechanism, the cavity formation mechanism, and the intergranular selective oxidation mechanism [14][15][16][17][18][19][20][21][22]. Among them, the intergranular selective oxidation mechanism, which 2 was first proposed by Scott et al [23] and further developed in the following papers [6,13,21,24,25], seems to most closely explain the cracking of Alloy 600 in the PWR primary water conditions. According to the intergranular selective oxidation mechanism, the basic assumption is that grain boundaries are preferentially oxidized once exposed to PWR primary water, becoming brittle and, therefore, susceptible to cracking.…”

Observation of internal oxidation in a 20% cold-worked Fe-17Cr-12Ni stainless steel through high-resolution characterization

“…Intergranular stress corrosion cracking (IGSCC) has affected structural materials exposed to primary water of pressurized water reactors (PWRs) [1][2][3][4]. To date, several mechanisms have been proposed that describe the mechanisms controlling IGSCC of austenitic alloys, including the slip-oxidation model [5], the hydrogen embrittlement model [6], the creep-cavity model [7], and the internal oxidation model (IOM) [8][9][10][11]. The IOM was firstly proposed by Scott et al [8] in the study of IGSCC of Alloy 600 after exposure to the primary water of PWR.…”

The Effect of Temperature on the Preferential Intergranular Oxidation Susceptibility of Alloy 600

“…[30][31][32][33][34][35] In particular, recent studies by Bertali et al [30] have unequivocally demonstrated the occurrence of pronounced grain boundary (GB) migration (lateral movement by~300 nm in 120 hours) during oxidation of Alloy 600SA in a high-temperature (480°C) H 2 -steam environment. They detected fine intergranular M 23 C 6 carbides, formed during the waterquench, that served as ''markers'' denoting the original boundary position and enabled GB movement away from the carbides during the high-temperature exposure to be measured, thereby confirming that GB migration occurred during the high-temperature oxidation.…”

“…Furthermore, they suggested that this mechanism could play an important role in the IGSCC initiation process and in enhancing the O and Cr diffusivities. Although the first conclusive demonstration of this localized DIGM occurring in advance of the PIO was obtained at 480°C in a H 2 -steam slightly reducing environment with respect to the Ni/NiO transition, [30,34,35] it was considered that the temperature of the tests (480°C) was too high and that this might change the dominant mechanism responsible for IGSCC initiation.…”