Intergranular Stress Corrosion Cracking Research Articles

Review on Environmentally Assisted Static and Fatigue Cracking of Al-Mg-Si-(Cu) Alloys

This paper reviews the relevant literature and covers the main aspects of the environmentally assisted cracking of Al-Mg-Si-(Cu) alloys. Apart from a brief overview of the major microstructural and mechanical properties, it presents research results on the corrosion sensitivity and stress corrosion susceptibility of Al-Mg-Si alloys. Possible mechanisms of stress corrosion cracking and corrosion fatigue in aluminum alloys, such as anodic dissolution and/or interaction with hydrogen, are considered. A number of factors, including atmospheric or solution conditions, applied stress, and material properties, can affect these mechanisms, leading to environmentally assisted cracking. Specific attention is given to Al-Mg-Si alloys with copper, which may increase the sensitivity to intergranular corrosion. The susceptibility to both intergranular corrosion and stress corrosion cracking of Cu-containing Al-Mg-Si alloys is mostly associated with a very thin layer (segregation) of Cu on the grain boundaries. However, the effect of Cu on the corrosion fatigue and fatigue crack growth rate of Al-Mg-Si alloys has received limited attention in the literature. At the current state of the research, it has not yet been holistically assessed, although a few studies have shown that a certain content of copper can improve the resistance of aluminum alloys to the environment with regard to corrosion fatigue. Furthermore, considerations of the synergistic actions of various factors remain essential for further studying environmentally assisted cracking phenomena in aluminum alloys.

Evaluation of Sensitization Behaviors on the Heat-Affected Zone of Austenitic Stainless Steel Weld by Thermal Cycles of Actual Multi-pass Welding

AbstractThe sensitization behavior of the welding heat affected zone (HAZ) in austenitic stainless steels (SSs) was investigated through simulated thermal cycles emulating actual multi-pass welding processes using the Gleeble simulator. The tests were performed with austenitic SSs, considering carbon contents, heat input, and distance from the fusion line to determine the thermal cycle conditions of the HAZ. Higher carbon content led to increased sensitization (degree of sensitization, DOS) values, while the influence of the thermal cycle in the final weld pass was that even though it was rapidly heated to over 1000 °C and cooled at a rapid rate, the DOS value decreased due to partial carbide dissolution and chromium diffusion. Therefore, effective management of the final thermal cycle in the HAZ contributes to improved intergranular stress corrosion cracking resistance. Even with prolonged exposure of the HAZ to the sensitization region, the discovery that corrosion resistance improves when the final heating cycle reaches 1000 °C underscores the importance of HAZ heat cycle management and provides valuable insights for materials engineering and industrial applications. Graphical abstract

A novel surface grain boundary engineering approach to improving corrosion resistance of a high-N and Ni-free austenitic stainless steel

Grain boundary engineering (GBE) can effectively improve the corrosion resistance of materials, but the traditional thermal-mechanical process still exhibits some limitations. In the present work, a novel surface spinning strengthening (3 S) technology followed by heat treatment was applied to modify the microstructure near the surface (∼ 400 μm) of a high-N Ni-free austenitic stainless steel. Under an optimal condition of annealing at 1323 K for 60 min after 3 S, the fraction of special boundaries mainly involving Σ3 boundaries in GBE layer was significantly improved from 48.3 % to 69.1 %, thus achieving excellent resistances to intergranular corrosion and stress corrosion cracking.

Fractography of Stress Corrosion Cracking of 20% Cold Worked Type 304 H Stainless Steel Containing δ-Ferrite in Oxidizing Primary Water

Fractography of stress corrosion cracking (SCC) of 20% cold worked Type 304 H stainless steel containing δ-ferrite was studied using a compact tension (CT) specimen in oxidizing primary water with a scanning electron microscope (SEM) and electron back scattered diffraction (EBSD). The stress corrosion crack propagated mostly in transgranular stress corrosion cracking (TGSCC) mode and sometimes in intergranular stress corrosion cracking (IGSCC) mode. TGSCC paths were along the {111} plane with both high resolved shear stress and high resolved tensile stress. IGSCC preferentially propagated along the grain boundary perpendicular to the loading axis. The findings in this work suggest that TGSCC proceeds through formation of a weakening zone at the head of the crack tip by interaction of slip and corrosion and then cracking of the weakened zone by tensile stress.

Revealing the Nanoscopic Corrosive Degradation Mechanism of Nickel-Rich Layered Oxide Cathodes at Low State-of-Charge Levels: Corrosion Cracking and Pitting.

Ni-rich layered oxides have received significant attention as promising cathode materials for Li-ion batteries due to their high reversible capacity. However, intergranular and intragranular cracks form at high state-of-charge (SOC) levels exceeding 4.2 V (vs. Li/Li+), representing a prominent failure mechanism of Ni-rich layered oxides. The nanoscale crack formation at high SOC levels is attributed to a significant volume change resulting from a phase transition between the H2 and H3 phases. Herein, in contrast to the electrochemical crack formation at high SOC levels, another mechanism of chemical crack and pit formation on a nanoscale is directly evidenced in fully lithiated Ni-rich layered oxides (low SOC levels). This mechanism is associated with intergranular stress corrosion cracking, driven by chemical corrosion at elevated temperatures. The nanoscopic chemical corrosion behavior of Ni-rich layered oxides during aging at elevated temperatures is investigated using high-resolution transmission electron microscopy, revealing that microcracks can develop through two distinct mechanisms: electrochemical cycling and chemical corrosion. Notably, chemical corrosion cracks can occur even in a fully discharged state (low SOC levels), whereas electrochemical cracks are observed only at high SOC levels. This finding provides a comprehensive understanding of the complex failure mechanisms of Ni-rich layered oxides and provides an opportunity to improve their electrochemical performance.

New insights into stress corrosion cracking mechanism of Alloy 600 in boiling water reactor (BWR) environment

Several mechanisms have been proposed to explain the intergranular stress corrosion cracking (IGSCC) of Alloy 600 in BWR, but slip-dissolution at grain boundaries remains the most recognized cause. However, it is still uncertain whether the above degradation is accompanied by selective internal oxidation (SIO) as a precursor. Following new insights into the creviced bent beam (CBB) test, relevant evidence was discovered. Additionally, the results of First Principle Calculation indicate interstitial O actively competes for chromium in IG carbides to form chromium oxides during the SIO process, instead of passively waiting for the oxidation/decomposition of carbides to provide a chromium source.

Effect of the triangular prism dent on stress corrosion cracking behavior of alloy 690TT heat transfer tube in a lead-containing alkaline solution

In this paper, the microstructural changes and mechanical characteristics of alloy 690TT heat transfer tube with a triangular prism dent are investigated by combining experimental and simulation methods, and subsequently examines their influence on stress corrosion cracking (SCC) behavior. The results indicate that the deformation mechanism caused by impact dent is slip and twinning. The structural transformation of high-density dislocations, as well as Copper and Brass deformation textures, are formed at dent bottom, resulting in stress concentration through work hardening, which greatly increases SCC sensitivity. Oxidation preferentially occurs along grain boundaries and dislocations, and the corrosion products are formed, which exhibit a semi-coherent orientation relationship with the matrix. Oxidation is essentially a de-alloying process in which oxygen diffuses inward and Cr migrates towards the oxidation zone. The wedge force generated by corrosion products provides another driving force for initiation and propagation of SCC cracks, in addition to external loads and residual stress. SCC cracks propagate in the form of intergranular stress corrosion cracking and transgranular stress corrosion cracking in a high temperature lead-containing alkaline solution.

Intergranular corrosion of Ni-30Cr in high-temperature hydrogenated water after removing surface passivating film

High-resolution transmission electron microscopy and atom probe tomography are used to characterize the initial passivation and subsequent intergranular corrosion of degraded grain boundaries in a model Ni-30Cr alloy exposed to 360 °C hydrogenated water. Upon initial exposure for 1000 h, the alloy surface directly above the grain boundary forms a thin passivating film of Cr2O3, protecting the underlying grain boundary from intergranular corrosion. However, the metal grain boundary experiences severe Cr depletion and grain boundary migration during this initial exposure. To understand how Cr depletion affects further corrosion, the local protective film was sputtered away using a glancing angle focused ion beam. Upon further exposure, the surface fails to repassivate, and intergranular corrosion is observed through the Cr-depleted region. Through this combination of high-resolution microscopy and localized passive film removal, we show that, although high-Cr alloys are resistant to intergranular attack and stress corrosion cracking, degradation-induced changes in the underlying metal at grain boundaries make the material more susceptible once the initial passive film is breached.

Electrochemical Evaluation of Al-5 wt% Zn Metal-Rich Primer for Protection of Al-Zn-Mg-Cu Alloy in NaCl

An intact and X-scribed Al-5wt%Zn-rich primer (AlRP) without pretreatment or topcoat was evaluated for its ability to suppress potential-dependent intergranular corrosion and intergranular stress corrosion cracking of peak-aged AA7075A-T651 in NaCl salt fog and full immersion. The ability of the primer to provide sacrificial anode-based cathodic prevention of peak-aged AA7075-T651 substrate was evaluated both under the primer coating and at scratches. The AlRP evaluated consisted an epoxy-based resin embedded with spherical Al-5wt%Zn pigment particles. Performance was evaluated under full immersion in 0.6 M NaCl solution and compared to ASTM B117 salt spray exposure using two approaches. These consisted of the University of Virginia (UVA) cycle test on intact coatings and the full immersion galvanic couple testing on simulated scratched panels created when intact coatings form bimetal couples with bare AA7075-T651. Focus was placed on the ability of the AlRP to achieve a targeted intermediate galvanic couple potential near a “prevention” potential which suppresses stress corrosion crack growth, intermetallic particle corrosion as well as intergranular corrosion. The long-term (24-h) open-circuit potential (OCP) of AlRP-coated AA7075-T651 in 0.6 M NaCl indicated that the AlRP provided less than 100 mV of cathodic potential shift of the intact coating from its OCP in 0.6 M NaCl. Electrochemical cycle testing conducted at a potentiostatic hold of –0.95 VSCE demonstrates that the AlRP did not enable sacrificial anode-based cathodic protection as the coupled potential remained at the corrosion potential of bare AA7075-T651. Furthermore, the current observed throughout galvanic corrosion experiments coupling of AlRP to AA7075-T651 indicated the AlRP coating was a cathode in the bimetal galvanic couple. ASTM B117 salt spray exposure of the AlRP revealed oxidation of the AA7075-T651 substrate below the primer detected as a continually growing oxygen signal at the primer-substrate interface that did not arrest corrosion over the exposure period.

Sensitization and stress corrosion cracking characteristics of 5059 alloy vis-à-vis 5083 alloy after reversion treatments

Moderately higher than room temperature exposures can sensitize marine grade 5xxx series aluminum alloys, making them susceptible to intergranular corrosion and stress corrosion cracking in marine environments. Sensitization occurs due to precipitation of active, magnesium-rich β phase along the grain boundaries. Higher strength, high-magnesium 5059 and 5083 grade alloys were artificially sensitized by thermal exposures at 60 °C, 80 °C and 150 °C for various durations of 1, 4, 15, 41, and 100 days. Sensitization and stress corrosion cracking responses are compared. 5059 alloy exhibited a higher degree of sensitization of 86 ± 1 mg/cm2 as compared to 64 ± 2 mg/cm2 of 5083 alloy, for the similar sensitization condition of 150 °C–15 days. This is attributed to the higher content and therefore super-saturation of magnesium in the former. In order to restore the corrosion resistance, reversion treatments involving re-exposing the sensitized alloys to elevated temperatures for short durations of 10 to 30 min were performed. Degree of sensitization after reversion treatment is evaluated leading to identification of conditions for obtaining safe values (<15 mg/cm2) without compromising the mechanical properties much. Optimum reversion treatment employed 30 min of exposures at 230 °C.

Determining SCC resistance of stainless steel claddings in high- temperature water by constant load crack growth tests and slow strain rate tests

Stress corrosion cracking (SCC) behaviors of 309 L and 308 L weld overlays are characterized in oxygen-free and oxygen-bearing high-temperature water using slow strain rate tests (SSRTs) and crack growth rate (CGR) tests with compact tension specimens. There is no apparent SCC indication on 308 L, while local SCC is observed on 309 L after SSRT in oxygen-free water. The SCC sensitivities of 308 L and 309 L increase with the increase of dissolved oxygen (DO) content, while 308 L shows relatively higher SCC resistance than 309 L in water with 200 ppb and 8000 ppb DO. SSRT and CGR test results show a similar effect of DO concentration on SCC of 309 L and 308 L. The fracture surface of 309 L exhibits extensive intergranular SCC, while 308 L shows only local interdendritic SCC after CGR tests. The crack tip blunting decreased the CGR in the low alloy steel. The highly island-shaped δ-ferrites and moderate strain hardening in 308 L contribute to its SCC resistance over 309 L.

Effect of material chemical composition on oxidation and stress corrosion cracking of the submerged arc welding Alloy 52M overlay in a simulated PWR primary water

Compact tension (CT) specimens from submerged arc welding Alloy 52 M overlay are used to determine the stress corrosion cracking (SCC) resistance of the dilution zones and bulk overlay metal on the 52 M side in a simulated pressurized water reactor (PWR) primary water. SEM-EDS and X-ray fluorescence spectroscopy (XRF) results show three dilution zones (DZs) on the 52 M side. Oxidation test results show that the thickness of the compact oxide layer and maximum local oxidation penetration depth decrease for 1st DZ, 2nd DZ, and bulk 52 M, which are consistent with the average SCC growth rate and the number of local intergranular SCC cracks in these regions. The dilution zones with low Cr but high Fe content possess lower oxidation and SCC resistance than the bulk 52 M.

Cause analysis of surface cracks in flash butt welding joint of high manganese steel frog

Surface cracking is one of the typical failures in butt welding joints of high manganese steel railway frogs. Understanding the formation mechanism of such cracks can effectively prevent similar failures from occurring. Herein, assisted with multiple macro and micro characterization tools, we discussed the causes of surface crack formation for a flash butt welding joint of a high manganese steel frog. The results show that the surface cracks are typical intergranular stress corrosion cracks (IGSCC) distributed near the fusion line between the carbon steel rail and the stainless steel medium in the stainless steel side. Acicular martensite exists near the fusion line between carbon steel rail and stainless steel medium, and the residual stress is large. At the same time, there are continuous network chromium carbide precipitates on the austenitic grain boundary of stainless steel. The above two points should be the main reasons for the initiation of cracks on the weld surface. Reduce the proportion of martensite structure by reasonably optimizing the welding cooling rate. Properly temper martensite to reduce the hardness and internal stress in the transition zone. These measures can prevent the occurrence of intergranular cracks on the weld surface.

Precipitation Behavior and Corrosion Properties of Stirred Zone in FSWed AA5083 Al-Mg Alloy after Sensitization

This paper investigated the Mg-rich phase precipitation behavior and the corrosion performance throughout the thickness direction within the stirred zone (SZ) of friction stir welded (FSW) AA5083 alloy after 175 °C/100 h sensitization. For the as-welded SZ, the recrystallized grain size gradually decreased from the top surface (5.5 μm) to the bottom (3.7 μm). The top and bottom of the SZ maintained relatively high levels of deformed grains and accumulated strain induced by either shoulder pressing or pin stirring. After 175 °C/100 h sensitization, 100 nm thick β′-Al3Mg2 precipitates were present along the grain boundaries (GBs) in the SZ. The bottom of the SZ exhibited more continuous precipitates along GBs due to the fine grain size and the large fraction of high-angle grain boundaries (0.724%). Although the as-welded SZ exhibited excellent corrosion resistance, it became extremely vulnerable to intergranular cracking (IGC) and stress corrosion cracking (SCC) after sensitization. The large SCC susceptibility indices of the SZ samples ranged from 66.9% to 73.1%. These findings suggest that sensitization can strongly deteriorate the corrosion resistance of the Al-Mg FSW joint, which is of critical importance for the safety and reliability of marine applications.

Monte Carlo simulation of stress corrosion cracking in welded metals

Stress corrosion cracking (SCC) behavior in welded metals is strongly affected their microstructures because the metals have complicated microstructures with broad grain size distributions. It is required to develop a lifetime evaluation technique considering SCC behavior which is affected by the microstructure. The present study aimed to develop a Monte Carlo simulation of intergranular SCC in welded metals, and crack initiation, coalescence, and growth were modeled considering their scatter based on the microstructure. Then, the simulation was applied to a welded nickel-based alloy in simulated primary coolant water for pressurized water reactors. The results showed that scatter in crack growth shortened the lifetime, while scatter in crack initiation and coalescence only slightly affected it.

Complete Desensitization of Aluminum–Magnesium Alloys via Boron Addition

We address here an important issue related to sensitization effects in Al5083 by mitigating the grain boundary precipitation of the beta phase and demonstrate that the addition of a small amount of boron to Al5083 impedes the precipitation of the beta phase, Al3Mg2, also known as the Samson phase. In Al–Mg alloys, the precipitation of Al3Mg2 usually occurs at grain boundaries in the temperature range of 50 to 200 °C from a supersaturated solid solution of Al–Mg and makes these alloys susceptible to intergranular corrosion and stress corrosion cracking. Upon boron addition, we show, using transmission electron microscopy, that a diboride phase, AlMgB2, forms at grain boundaries instead of the beta phase upon extended annealing at 150 °C. This diboride phase does not dissolve in saltwater, suggesting it is less anodic relative to the matrix. To quantify and compare the dissolution characteristics, we carried out nitric acid mass loss test for Al5083 samples containing 3 wt.% boron treated at 190 h at 150 °C, and fully sensitized Al5083 samples containing 0.0 wt.% boron. We estimate the mass loss to be 4 mg/cm2 for boron containing samples as compared to the mass loss of 45 mg/cm2 for samples without boron, indicating that the addition of boron is highly effective in suppressing the susceptibility to intergranular corrosion in Al5000 series alloys. This provides a potential route to minimize the longstanding problem of ship structure sensitization.

Radiochemical behavior of nitrogen species in high temperature water

The water radiolysis in-core at light water reactors (LWRs) produces various radicals with other ionic species/molecules and radioactive nitrogen species in the reactor coolant. Nitrogen species can exist in many different chemical forms and recirculate in water and steam, and consequently contribute to what extent the environmental safety at nuclear power plants. Therefore, a clear understanding of formation kinetics and chemical behaviors of nitrogen species under irradiation is crucial for better insight into the characteristics of major radioactive species released to the main steam or relevant coolant systems and eventually development of advanced processes/methodologies to enhance the environmental safety at nuclear power plants. This paper thus focuses on basic principles on electrochemical interaction kinetics of radiolytic molecules and various nitrogen species in high temperature water, fundamental approaches for calculating thermodynamic values to predict their stability and domain in LWRs, and the effect of nitrogen species on crevice chemistry/corrosion and intergranular stress corrosion cracking (IGSCC) susceptibility of structure materials in high temperature water.

Mechanistic Insight into Al-Zn, Mg, and Al-Mg-Rich Primer Design for Enhanced Cathodic Prevention on Sensitized Al-Mg Alloys

Three Al-Zn, Mg, and Mg/Al-rich primers (RPs) were evaluated for their ability to suppress intergranular corrosion (IGC) and intergranular stress corrosion cracking (IG-SCC) on highly sensitized aluminum alloy 5456-H116 by sacrificial anode-based cathodic prevention and chemical deposition effects. Tests were conducted in a 0.6 M NaCl solution under full immersion. These evaluations considered the ability of the primer to attain an intermediate open-circuit potential (OCP) such that the galvanic couple potential with bare 5456 resided outside a range of potentials where IGC prevention is observed. The ability of the primer to achieve OCP’s negative enough so that the 5456-H116 could be protected by sacrificial anode-based cathodic prevention and the ability to sustain this function over time were evaluated. The primers consisted of epoxy resins embedded with either (1) spherical Al-5 wt% Zn, (2) spherical Al-5 wt% Zn and spherical Mg, or (3) Mg flake pigments. A variety of electrochemical techniques evaluated the performance specified including OCP, electrochemical impedance spectroscopy, diagnostic cycle testing, as well as zero resistance ammeter tests with simultaneous pH measurement. Electrochemical cycle testing demonstrated that Al-5%Zn did not activate or provide cathodic prevention. Mg-RP had a suitable OCP for cathodic protection of 5456 but the time to primer activation as well as the activated potential both decreased upon utilization of Mg flake content in the primer. The pure Mg-RP activated quickly but ceased to achieve protective potentials after 1 to 11 cycles of DC/AC/OCP cycle testing. Cross-sectional analysis demonstrated that some flakes dissolved while uniform surface oxidation occurred on the remaining Mg flakes, which in combination led to impaired activation. The composite Mg plus Al/Zn-RP mixed primer maintained a suitably negative OCP over time, remained activated, dispensed high anodic charge, and remained an anode in zero-resistance ammeter testing. Chemical stability modeling and zero-resistance ammeter testing suggest that Mg corrosion elevates the pH which activates the Al-5 wt% Zn pigments, thereby providing a secondary pathway for sacrificial anode-based cathodic protection which supports the long-lasting cathodic protection achieved by the Al-5 wt% Zn/Mg primer. These analyses set a baseline for the consideration of Al-Zn/Mg-based coatings to establish effective cathodic protection on highly sensitized 5456-H116 in an aggressive alternate immersion environment and illustrate the merit of using Al/Mg-RP.

Effect of Phosphorus in Copper Tubes on Intergranular Stress Corrosion Crack

アンモニア水溶液中における銅管の酸化溶出挙動について，リンがおよぼす影響を電気化学測定により調べた．その結果，最初に1価の[Cu（NH3）2]＋イオンへの酸化溶出が発生し，その後2価の[Cu（NH3）4]2＋イオンへの酸化溶出に移行すること，リンが後者の反応の電荷移動抵抗を低下させることがわかった．リンは銅の粒界に偏析し，その付近で銅が優先的に溶出していた．粒界に偏析するリンが粒界型応力腐食割れの一因と推定された．

Role of low-level void swelling on plasticity and failure in a 33 dpa neutron-irradiated 304 stainless steel

Radiation damage introduces a wide range of defects in structural materials depending on the irradiation conditions. Irradiation-induced loops are known to lead to dislocation-channeling, which reduces the work hardenability and increases the susceptibility to intergranular stress corrosion cracking. In a higher temperature regime, void formation is an integral radiation-induced defect type in addition to radiation-induced loops. Previous bulk mechanical tests suggest that a high level of void swelling can lead to severe embrittlement while a low level of void swelling does not negatively affect intergranular cracking and ductility. This study utilized microscale bicrystal testing to evaluate the role of low-level void swelling on dislocation-channel suppression and intergranular cracking in a 33 dpa neutron-irradiated 304 stainless steels with 2% and 3.7% void swelling. The results provided direct observation on the suppression of dislocation-channel and intergranular cracking in the presence of low-level void swelling.