Intergranular Stress Corrosion Cracking Research Articles

Effect of grain size and grain boundary type on intergranular stress corrosion cracking of austenitic stainless steel: A phase-field study

A phase-field model coupled with polycrystalline microstructure is utilized to investigate the effect of grain size and grain boundary types on intergranular stress corrosion cracking in austenitic stainless steels. Considering the dilute solution environment, the free energy density of the two phases is hypothesized to be in parabolic form. The slower corrosion crack propagation rate in coarse-grained microstructures can be attributed to a higher frequency of transgranular cracking. Low-angle grain boundaries can effectively deflect intergranular corrosion cracks into grains with lower corrosion susceptibility, thereby impeding crack propagation. Twin boundaries mitigate corrosion crack propagation by reducing potential initiation sites.

Grain boundary sensitization kinetics of cold-rolled Al–Mg alloys

As super-saturated solid solutions of Al-Mg, 5XXX series aluminum alloys are susceptible to sensitization via intergranular precipitation of the anodic β-phase, which promotes intergranular corrosion, exfoliation and stress corrosion cracking under environmental conditions. This study presents important updates to a Johnson–Mehl–Avarami–Kolmogorov (JMAK) type model for low-temperature sensitization, correlating the intergranular corrosion response to impingement of locally sensitized regions surrounding discrete β-phase grain boundary precipitates. It is demonstrated that the sensitization response of these alloys can be approached as a combination of two independent contributions: the geometric configuration of grain boundaries passing through the microstructure that are most prone to sensitization, and the rate that these boundaries sensitize due to the formation of the β-phase. This allows for the large sensitization response variations found between nominally identical materials produced by different suppliers, which originate due to a lack of constraints within current cold-rolled plate tempers, to be removed as a sample-dependent linear scaling factor that is separate of the rate kinetics. The JMAK model describes the kinetics of 5xxx series sensitization with excellent accuracy across all data available in the literature. The results of the model imply that sensitization at environmental temperatures proceeds via a site-saturated process, with the β-phase forming on a set density of preferential nucleation sites. It is shown that site-saturation allows for extension of the JMAK model to non-isothermal aging profiles and supports a diffusion pathway dominated by pipe diffusion to the interface followed by precipitate growth via the collector plate mechanism.

Stress Corrosion Cracking of Manganese Bronze in Water

AbstractContinuous and centrifugal cast manganese bronze parts (C86300) experienced intergranular cracking in as few as 24 h after being stored outside. C-ring tests according to ASTM G38 were conducted to assess the material’s susceptibility to stress corrosion cracking (SCC) susceptibility and found that water was the most likely agent. The failure mechanism has been identified as intergranular SCC due to a combination of residual stress from a rough machining operation and water from rain or dew. To prevent cracking, a stress relief heat treatment immediately after the rough machining operation is recommended.

Determining the microstructure effects on the stress corrosion cracking initiation behavior of laser powder-bed-fusion printed 304L stainless steel in high-temperature hydrogenated water

This study investigated the microstructure effects on the stress corrosion cracking (SCC) initiation behavior of laser powder-bed-fusion (L-PBF) printed 304 L stainless steel in high-temperature hydrogenated water. The dislocation cells facilitate Cr transportation, thereby mitigating intergranular oxidation and SCC initiation. Compared to the warm-rolled dislocation cells, as-printed dislocation cells result in reduced strain localization, which is beneficial for suppressing SCC initiation. This is because the as-printed dislocation cells are stable and composed of abundant screw dislocations. Micro-inclusions can lead to nodular corrosion, thus increasing the depth of intergranular oxidation and promoting SCC initiation.

Achieving high mechanical and corrosion properties of AA2050 Al-Li alloy: The creep aging under plastic loading

The influences of elastic/plastic loading (100–220 MPa) on the creep behavior, mechanical properties, and corrosion behavior of creep-aged AA2050 alloys were investigated. The results show that the creep rate increased from 0.35 % to 0.61 % with the increase of stress from 100 MPa to 220 MPa. The creep rate was increased rapidly under plastic loading (220 MPa) due to the increased dislocation density. Meanwhile, the plastic loading shortened the peak-aged time of creep-aged alloys and achieved outstanding strength (UTS=534 MPa, YS=496 MPa, peak aged), which increased by 33 MPa and 32 MPa compared with elastic loading, respectively. The strength enhancement was attributed to the increase in dislocation density, weak oriented precipitation effect, and dense precipitation of T1 phases. Additionally, compared with elastic loading, GBPs under plastic loading coarsened and distributed discretely, their elements content distributed evenly, and the Cu content increased. Therefore, the intergranular corrosion (IGC) depth and stress corrosion cracking (SCC) susceptibility index (ISSRT) decreased from 174 μm, and 8.7 % to 121 μm, and 5.9 %, respectively. These findings pave a way in breaking curvature limit of creep aging technology.

Intergranular corrosion and stress corrosion cracking properties evaluation and mechanism study of multi-microalloyed 2519 Al alloy

In this paper, the microstructure of the alloy has been modulated by the multivariate microalloying technique, aiming to reveal the intrinsic relationship and mechanism of intergranular corrosion and stress corrosion cracking. The addition of V to 2519 alloy changed the distribution characteristics of grain boundary precipitates and the dislocation density was reduced by 22.5 %, and the intergranular and stress corrosion cracking properties of the alloy were improved by 14.1 % and 40.7 %, respectively. Interestingly, grain deflection with <XXY>/48°-58° axial angle relationship was found during stress corrosion crack propagation and the alloy had the best stress corrosion resistance.

Improving intergranular cracking and stress corrosion cracking resistance of highly sensitized AA5083 Al-Mg alloy via reversion heat treatment

This study systematically examines the impact of reversion heat treatments (220–280 ℃ for 1 h) on the microstructure evolution, electrochemical corrosion, intergranular cracking (IGC) and stress corrosion cracking (SCC) of a severely sensitized (175 ℃/100 h) AA5083 alloy. Increasing the reversion temperature gradually enhances the corrosion resistance by dissolving the β′-Al3Mg2 phase, with the optimal treatment identified as 280 ℃/1 h. The βˊ phase maintains its planar film shape and continuously covers the grain boundaries after reversion treatment below 240 °C, but spheroidizes at the triple junctions at 260 °C. The morphology of the βˊ phase is dictated by grain boundary diffusion and interface diffusion. Reversion treatments improve SCC resistance by dissolving the β′ phase and reducing yield strength, attributed to anodic dissolution and hydrogen embrittlement mechanisms. This research offers valuable insights into the practical benefits of reversion treatments for Al-Mg alloy marine applications, addressing safety concerns related to sensitization.

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

The 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.

Evaluation of fracture resistance behavior of Alloy 690 material upto 1000°C

Alloy 690 is a nickel-based alloy with a nominal composition of 30% Cr and 10% Fe (wt%). It is denoted as Ni-30Cr-10Fe. This alloy is currently being investigated by various researchers for its use in nuclear industry as a possible replacement of alloy 600 steam generator tubes because of its excellent resistance to inter-granular stress corrosion cracking in water reactor environment. Alloy 690 is mainly used in vitrification melters for immobilization of high level waste in nuclear recycle plant. The temperature of water reactor environment is considerably lower compared to that of vitrification application, where temperature can reach an order of 1000 to 1100˚C. The mechanical and fracture properties of alloy 690 at the elevated temperature is important from the point of view of design and safety analysis of vitrification melter components and it is not available in literature. For this purpose, single edged notched tensile specimens have been fabricated from alloy 690 plates of 10 mm thickness. The fracture specimens have been tested in the temperature range of 25˚C to 1000˚C, which is the operating range of vitrification melters. The crack initiation toughness was obtained using modified blunting line equation in order to account for material strain hardening effect at a given temperature. From the fracture test results, it was observed that the initiation toughness is lowest at 700˚C. To understand this behavior, scanning electron microscopy was carried out on the fracture surface of the tested specimens. The fracture surface of the specimen tested at 700˚C showed presence of brittle phases in the microstructure, which are responsible for lower value of fracture toughness at this condition. The results of this work shall be useful for design and analysis of vitrification melter components.

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.