•Residual strain and GBCD change as a function of the distance from FB in 316L HAZ.•Neither type II boundary nor obvious carbon-depleted zone is found in SA508 HAZ.•No carbon concentration is found at the SA508-52 interface.•The middle part of the DMWJ has the highest residual strain.The microstructure, residual strain and interfacial chemical composition distribution of a safe-end dissimilar metal weld joint (DMWJ, SA508-52-316L) prepared by narrow-gap gas-tungsten arc welding (NG-GTAW) were studied by optical microscope (OM) and scanning electron microscope equipped with an energy dispersive X-ray microanalysis (SEM/EDX) and an electron back scattering diffraction (EBSD) system. Complex microstructure and chemical composition distribution are found, especially at the SA508-52 interface and the 52-316L interface. In brief, a complicated microstructure transition exists within the SA508 heat affected zone (HAZ); the residual strain, the fraction of high angle random grain boundaries and low angle boundaries decrease with increasing the distance from the fusion boundary in 316L HAZ; neither typical type II boundary nor obvious carbon-depleted zone is found near the SA508-52 interface; dramatic and complicated changes of the contents of the main elements, Fe, Cr and Ni, are observed at the distinct interfaces, especially at the SA508-52 interface. No carbon concentration is found at the SA508-52 interface.

•SCC of FB for 316L/52M weld joint was studied in high temperature water.•The cracks are blocked when propagated into the composition transient zone.•SCC cracking mode at FB is both intergranular and transgranular.•CGR of FB is larger than that at HAZ in hydrogenated water.The stress corrosion cracking (SCC) crack growth rates (CGRs) at the fusion boundary (FB) for 316L/52M weld joints were measured using direct current potential drop systems in borated and lithiated high temperature water. The cracks propagated along the FB and were blocked after propagating into the composition transient zone. The cracking mode is both intergranular and transgranular. The CGRs at the FB are similar to those in the heat-affected zone (HAZ) in oxygenated water, but slightly higher than those in the HAZ in hydrogenated water. The temperature dependences of CGR in both hydrogenated and oxygenated water are discussed.

•SCC of 316L HAZ in dissimilar metal weld joint was studied in simulated PWR water.•Crack growth rates increased with increasing temperature and dissolved oxygen.•Temperature dependence on crack growth rates are consisted with 15–20% CW 316L SS.•Intergranular secondary cracks tended to propagate perpendicular to fusion boundary.The stress corrosion cracking (SCC) behaviour of 316L heat affected zones (HAZ) in 316L stainless steel/Inconel 52M dissimilar metal welded joint (DMWJ) in simulated primary water was systematically evaluated using direct current potential drop (DCPD) methods. Crack growth rates (CGRs) of 316L HAZ increased with increasing temperature and dissolved oxygen (DO) contents. CGR in hydrogenated water was approximately one order of magnitude slower than in oxygenated water. The fracture surface shows typical mixed intergranular-transgranular SCC characteristics and several fast finger-like cracks. Several intergranular secondary cracks, perpendicular to the main crack and fusion boundary, were also observed.

•The pits in A508 are stopped immediately by adding H3BO3 in NaCl solution.•No obvious Cl− enrichment exists in the pit after adding H3BO3 in NaCl solution.•Element B is enriched in the pit after adding H3BO3 in NaCl solution.The corrosion of the low alloy steel A508-alloy 52 M interface region in buffered and non-buffered chloride containing solutions was studied by using the scanning vibrating electrode technique (SVET), scanning ion-selective electrode technique (SIET), and time of flight secondary ion mass spectroscopy (ToF-SIMS). The typical pit in low alloy steel A508 formed in NaCl solution was stopped immediately when H3BO3 was added to the NaCl solution, and the pit became cathodic. With increasing immersion time, H3BO3 entered into the pit, and the corrosion of A508 became general corrosion.

The influence of conductivity on corrosion behavior of 304 stainless steel (SS) in high temperature water was investigated by using in-situ potentiodynamic polarization curves, electrochemical impedance spectra (EIS) at 300 °C, and ex-situ scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The structures of oxide films formed on 304 SS change with different conductivities at 300 °C. With the increase in conductivity, the passive current density increases while the resistances of oxide films decrease. But the resistances do not decrease lineally with the increase in conductivity. A modified double-layer model for oxide structure was proposed to explain the influence mechanism of conductivity on the oxide films on 304 SS in high temperature water. Improving the 10B enrichment level can reduce the conductivity of primary water and increase the corrosion resistance of 304 SS.

Austenitic stainless steels are usually chosen to make many components of nuclear power plants (NPPs). However, their microstructure in the heat-affected zone (HAZ) will change during the welding process. Some failures of the weld joints, mainly stress corrosion cracking (SCC), have been found to be located in the HAZ. In this research, the microstructure, micro-hardness, residual strain and SCC behavior at different locations of the 316L HAZ cut from a safe-end dissimilar metal weld joint were studied. However, traditional optical microscope observation could not find any microstructural difference between the HAZ and the base metal, higher residual strain and micro-hardness, and higher fraction of random high-angle grain boundaries were found in the HAZ than in the base metal when studied by using electron back-scattering diffraction scanning and micro-hardness test. What’s more, the residual strain, the micro-hardness and the fraction of random grain boundaries decreased, while the fraction of coincidence site lattice grain boundaries increased with increasing the distance from the fusion boundary in 316L HAZ. Creviced bent beam test was applied to evaluate the SCC susceptibility at different locations of 316L HAZ and base metal. It was found that the HAZ had higher SCC susceptibility than the base metal and SCC resistance increased when increasing the distance from the fusion boundary in 316L HAZ.

The microstructure, local mechanical properties and local stress corrosion cracking susceptibility of an SA508-52M-316LN domestic dissimilar metal welded safe-end joint used for AP1000 nuclear power plant prepared by automatic gas tungsten arc welding was studied in this work by optical microscopy, scanning electron microscopy (with electron back scattering diffraction and an energy dispersive X-ray spectroscopy system), micro-hardness testing, local mechanical tensile testing and local slow strain rate tests. The micro-hardness, local mechanical properties and stress corrosion cracking susceptibility across this dissimilar metal weld joint vary because of the complex microstructure across the fusion area and the dramatic chemical composition change across the fusion lines. Briefly, Type I boundaries and Type II boundaries exist in 52Mb near the SA508-52Mb interface, a microstructure transition was found in SA508 heat affected zone, the residual strain and grain boundary character distribution changes as a function of the distance from the fusion boundary in 316LN heat affected zone, micro-hardness distribution and local mechanical properties along the DMWJ are heterogeneous, and 52Mw-316LN interface has the highest SCC susceptibility in this DMWJ while 316LN base metal has the lowest one.

In high-temperature and high-pressure water, traditional anticorrosion approaches are not suitable to be used to protect structural materials from oxidation and corrosion. In this study, monolayer graphene was explored as a barrier to protect the materials from degradation. The oxidation and corrosion rate of the monolayer-graphene-coated copper is much lower than that of the bare copper, suggesting that the monolayer graphene can effectively protect the copper from oxidation and corrosion in the simulated primary water of pressurized water reactors.

Effect of ethanolamine (ETA) on Alloy 690 in simulated pressurized water reactor (PWR) secondary cooling water was studied by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, atomic force microscopy (AFM), Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), X-ray photoelectron spectrometer (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). The results show that moderate addition of ETA can enhance the corrosion resistance of Alloy 690 in high-temperature pressurized water and the optimum additive value is 2 mg/L. The addition of ETA contributes to the formation of oxide rather than hydroxide in the film on the surface of Alloy 690. The corrosion resistance of Alloy 690 at 320 °C with the addition of ETA is better than that at 280 °C.

To explore the usage of monolayer graphene as an anti-oxidation barrier in simulated primary water of pressurized water reactors (PWRs), we transferred the monolayer graphene synthesized by low pressure chemical vapor deposition (LPCVD) on Cu foil to Alloy 690TT. After a 500 h immersion, strong oxidation resistance was obtained from the graphene coated Alloy 690TT sample, indicating that the transferred monolayer graphene can act as an effective barrier to protect the substrate from oxidation in simulated primary water of PWRs.

Initial corrosion kinetics of X52 anti-H2S pipeline steel exposed to 90 °C/1.61 MPa H2S solutions was investigated through high temperature and high pressure immersion tests. Corrosion rates were obtained based on weight loss calculation. The corrosion products were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and electron probe micro-analysis (EPMA). The initial corrosion kinetics was found to obey the exponential law. With increasing immersion time, the main corrosion products changed from iron-rich mackinawite to sulfur-rich pyrrhotite. The corrosion films had two layers: an inner fine-grained layer rich in iron and an outer columnar-grained layer rich in sulfur. The corrosion film formed through the combination of outward diffusion of Fe2+ ions and inward diffusion of HS− ions. The variation of the corrosion products and compaction of the corrosion layer resulted in a decrease in the diffusion coefficient with increasing immersion time. The double-layered corrosion film formed after long time immersion acted as an effective barrier against diffusion.

Multilayer graphene as a potential anti-oxidation barrier to protect nickel foils from oxidation was studied in simulated primary water of pressurized water reactors (PWRs). The results show that after immersion for 1000 h, the structure of the multilayer graphene remains unchanged and no obvious oxide film formed on the graphene coated nickel foils, indicating multilayer graphene can effectively act as the anti-oxidation barrier to protect the substrate from oxidation and hence can improve the heat transfer efficiency of the substrate in simulated primary water of PWRs.

Stress corrosion crack growth tests of a cold worked nuclear grade 316L stainless steel were conducted in simulated pressurized water reactor (PWR) primary water environment containing various dissolved oxygen (DO) contents but no dissolved hydrogen. The crack growth rate (CGR) increased with increasing DO content in the simulated PWR primary water. The fracture surface exhibited typical intergranular stress corrosion cracking (IGSCC) characteristics.

The aim of this study is to evaluate the effects of Ag3Sn intermetallic compounds (IMCs) on corrosion of Sn-3.0Ag-0.5Cu (SAC305) solder alloy under high-temperature and high-humidity condition. The Ag3Sn IMCs of SAC305 with various size and morphology were obtained by changing cooling rate. Commercial SAC305 solder with smallest Ag3Sn IMCs exhibits better corrosion resistance than air-cooled and furnace-cooled SAC305 solders because microgalvanic corrosion between large cathodic Ag3Sn IMCs plates and anodic Sn matrix decreased the corrosion resistance of air-cooled and furnace-cooled SAC305 solders.Highlights► The corrosion of solder under humidity due to the microgalvanic corrosion. ► Commercial SAC305 with smaller size of Ag3Sn exhibits better corrosion resistance. ► It was postulated the occurrence of reaction between Sn and O2, Ag3Sn and O2.

The effects of surface state and applied stress on the stress corrosion cracking (SCC) behaviors of thermally treated (TT) Alloy 690 in 10 wt% NaOH solution with 100 mg/L litharge at 330 °C were investigated using C-ring samples with four kinds of surface states and two different stress levels. Sample outer surfaces of the first three kinds were ground to 400 grit (ground), shot-peened (SP) and electro-polished (EP) and the last one was used as the as-received state. Two samples of every kind were stressed to 100% and 200% yield stress of Alloy 690TT, respectively. The results showed that the oxide film consisted of three layers whereas continuous layer rich in Cr was not found. The poor adhesive ability indicated that the oxide film could not protect the matrix from further corrosion. Lead was found in the oxide film and the oxides at the crack paths and accelerated the dissolution of thermodynamically unstable Cr in these locations and also in the matrix. The crack initiation and propagation on Alloy 690TT were effectively retarded by SP and EP treatments but were enhanced by grinding treatment, compared with the cracks on the as-received surface. The cracking severity was also enhanced by increasing the externally applied stress. The accelerated dissolution of Cr and the local tensile stress concentration in the near-surface layer caused by cold-working and higher applied stress reduced the SCC-resistance of Alloy 690TT in the studied solution.

The effect of microstructure and corrosion on fracture behavior of Sn–3.0Ag–0.5Cu (SAC305) solder alloy was in-situ studied at three-point bending test using environmental scanning electron microscopy (ESEM). The results showed that the microcracks initiated at the Sn boundaries in the β-Sn region for commercial SAC305 solder. For furnace-cooled SAC305 solder, cracks preferred to initiating and propagating along Sn boundaries and Sn/Ag3Sn interface. Ag3Sn plates were easily broken during the bending test. The fracture behavior was significantly affected by corrosion. The most vulnerable area to fracture is the corroded region of the specimen.