Intergranular Corrosion Sensitivity Research Articles

Microstructure and localized corrosion properties of 2219 aluminum alloy manufactured by additive friction stir deposition

Multi-layer 2219 aluminum alloy samples were successfully fabricated using additive friction stir deposition (AFSD). AFSD deposition reduced grain size and the size of intermetallic Al2Cu particles, but greatly increased the amount of Al2Cu particles. More Al2Cu particles increased the number of galvanic microcells on alloy surface and at the grain boundaries, which promoted the localized corrosion and improved the intergranular corrosion sensitivity of AFSD alloy. Subsequent T6 heat treatment had little effect on grain size but enhanced the corrosion resistance of AFSD alloy, primarily attributed to the reduction in Al2Cu particles and the elimination of dislocations within grains.

Revealing the intergranular corrosion mechanism of AA5083 alloys through experiments and atomic-scale computation

Continuously exposure to elevated temperature, known as sensitization, can accelerate the precipitation of the electrochemically active β phase (Al3Mg2) at grain boundaries (GBs) in Al-Mg alloys. This results in intergranular corrosion (IGC), which seriously affects the application of Al-Mg alloys in marine environments. Low-angle GBs (< 15°) are considered to restrict the nucleation and growth of the β phase, while high-angle GBs (> 15°) can promote these processes. However, the quantitative relationship between GB misorientation and IGC sensitivity at atomic scale is unknown. Herein, the underlying mechanism of IGC in AA5083 alloys with β phase and GB misorientation is investigated by experiments and simulation. The experimental results show that after sensitization when the misorientation angle exceeded 22.6°, the density of the β phase at GBs reaches up to 50 %–60 %. The hybrid molecular dynamics/Monte Carlo algorithm was utilized to simulate the diffusion of Mg and cluster formation in Al-5Mg alloy with 11 different GB models at 300 and 425 K. The maximum GB misorientation angle insensitive to IGC is about 18.9° to 22.6°. However, at 425 K, this angle decreases to 16.3°, increasing the IGC risk of Al-5Mg alloys. The calculation results provide valuable quantitative guidance for the corrosion resistance design of Al-Mg alloys.

Effect of Tempering Temperature on Microstructure and Intergranular Corrosion Property of 2205 Duplex Stainless Steel

The effect of tempering temperature on the microstructure and intergranular corrosion property of 2205 duplex stainless steel (DSS2205) was determined using a boiling acid intergranular corrosion test (boiling 65% nitric acid and 50% sulfuric acid–ferric sulfate), an optical microscope, a transmission electron microscope, and a double-loop electrochemical potentiokinetic reactivation (DL-EPR) test. The results show that the ferrite content of the DSS2205 is about 50% in a specimen close to a solid solution state (1050 °C for 1 h, then water-quenched) when tempered at 675 °C–725 °C for 1 h. As the tempering temperature rises to 750 °C–800 °C for 1 h, the ferrite content drops gradually from 49% to 35%. M23C6, FeCr (σ phase), and Cr2N phases are precipitated when the specimen is tempered at 675°C–800 °C for 1 h. When the tempering temperature rises to 750 °C–800 °C for 1 h, the content and size of σ phase increase significantly. In the boiling acid intergranular corrosion test, when the specimen is tempered at 675 °C–725 °C for 1 h, the corrosion rate is higher than when it is tempered at 750 °C–800 °C for 1 h. In the DL-EPR test, when the specimen is tempered at 675 °C–800 °C for 1 h, the intergranular corrosion sensitivity rises gradually. External polarization is added during the DL-EPR test, and the test principle is different from that of the boiling acid intergranular corrosion test, resulting in a different sensitivity to intergranular corrosion compared to boiling acid intergranular corrosion.

Influencing mechanisms of C content and aging treatment on intergranular corrosion sensitivity of 316 stainless steel weld metals

For analyzing the intergranular corrosion sensitivity of 316 stainless steel weld metals with different C contents, the intergranular corrosion behaviors of the weld metals under as-welded and different as-aged states were evaluated by both the H2SO4–CuSO4 solution corrosion method and the double loop electrochemical potentiokinetic reactivation method, respectively. The results indicate that after long term aging treatment at 550 °C, the δ ferrite in high C weld metal has a higher transformation fraction than that in low C weld metal, which results in a higher intergranular corrosion sensitivity for high C weld metal. However, after the long term aging treatment at 600 °C, the δ ferrite in high C weld metal transforms completely in the early stage aging, and with increasing of the aging time, the desensitization process occurs in the Cr-poor region of high C weld metal, which improves the intergranular corrosion resistance, and results in a higher intergranular corrosion sensitivity for low C weld metal. Therefore, under the service environment of considering the intergranular corrosion performance of the weld metal, the welding material with the appropriate C content should be selected according to the service temperature.

Effect of dissolved precursors on corrosion characteristics of Ni-based alloy Inconel 625, stainless steel 316L and titanium alloy TA2 in acidic and neutral supercritical water: A comparative study

This work investigated the corrosion characteristics of nickel-based alloy Inconel 625, stainless steel 316L (SS 316L), and commercial grade 2 titanium alloy (TA2) in ZrO(NO3)2-containing and ZrO(NO3)2/KOH-containing supercritical water (SCW) at 400 °C and 25 MPa. During ZrO(NO3)2-containing SCW exposure, Inconel 625 undergoes pitting and intergranular corrosion, while SS 316L and TA2 suffer uniform corrosion. Based on corrosion rate and metal oxide stability, the corrosion resistance follows an order of TA2 > Inconel 625 > SS 316L. The addition of KOH reduces the intergranular corrosion sensitivity of Inconel 625, and leads to different oxide distribution of SS 316L. The thick TiO2 oxide layer mixed with ZrO2 formed in ZrO(NO3)2/KOH-containing SCW enables TA2 to exhibit superior corrosion resistance than Inconel 625 and SS 316L.

Influence of precipitation on the intergranular corrosion sensitivity of aged Alloy 31 using a modified electrochemical potentiokinetic reactivation method

The influence of precipitation on the intergranular corrosion sensitivity of Alloy 31 aged at 950 ℃ for 0–96 h was investigated by microstructure analysis and the modified double loop electrochemical potentiokinetic reactivation method. The results reveal that the kinetics of the primary precipitated sigma phase agree with the Yamamoto equation. The degree of sensitization increases rapidly to 4 h, then decreases to 8 h with self-healing, but no further self-healing occurs after that. The degree of sensitisation depends on the Cr and Mo-depletion zone neighbouring the precipitated sigma phase.

Low-Potential Zone at the Interface of Precipitate and Austenite Affecting Intergranular Corrosion Sensitivity in UNS N08028 Nickel–Iron–Chromium Alloy

The precipitates and the intergranular corrosion behavior of a UNS N08028 nickel–iron–chromium alloy sensitized at different temperatures were studied by employing transmission electron microscopy, Kelvin probe force microscopy and other methods. It was found that sigma precipitates appeared at the grain boundaries of the alloy being sensitized. There was a Cr-depleted zone and a low-potential zone around these precipitates. The potential difference between the sigma precipitates and the low-potential zone was 102 mV, and this increased with the growth of the sigma precipitates. At this potential difference, the migration of the vacancies in the passive film accelerated significantly, and then the protectiveness of the passive film decreased. The intergranular corrosion mechanism of the steel has also be discussed.

Effects of the corrosion mechanism evolution of low silicon-cast aluminium alloys in service

ABSTRACT The corrosion mechanism evolution of four low silicon-cast aluminium alloys exposed to heat treatment at 200°C for 0–50 h was studied by means of immersion corrosion, intergranular corrosion and electrochemical test, SEM, EDS and EBSD analysis methods. The correlation of corrosion resistance with composition and the thermal exposure time was investigated. The results show that the corrosion mechanism of all aluminium alloys changed after thermal exposure at 200°C. Before thermal exposure, intergranular corrosion was the main corrosion, and after 200°C thermal exposure, serious pitting corrosion and spalling corrosion occurred in the local area. The contents of Si and Mg in the grain boundary increased obviously. The contents of elements in the poor zone of the grain boundary increased, and the electrical potential difference between the grain and the grain boundary reduced. The intergranular corrosion sensitivity of the alloy was reduced. But the degree of pitting gradually becomes serious. The electrochemical test of the aluminium alloy with 3.5 wt% Si showed that its corrosion potential increased with the increase inthermal exposure time, and its corrosion current density increased with the increase inthermal exposure time. After the EBSD test, it was found that the large angle grain boundary decreased gradually and the proportion of large grain size increased with the increase in thermal exposure time to 50 h.

Effects of grain boundary characteristics changing with cold rolling deformation on intergranular corrosion resistance of 443 ultra-pure ferritic stainless steel

The relationship between evolution in grain boundary characteristics and intergranular corrosion properties of cold rolled 443 ultra-pure ferritic stainless steel was investigated. The results showed that low-angle (LA) grain boundaries, special grain boundaries (SGB), and high-angle (HA) grain boundaries had a high intergranular corrosion sensitivity after cold deformation in reducing acid medium. In oxidative acid medium, the LA and SGB boundaries had a high intergranular corrosion resistance in comparison to HA boundaries, and their inhibitory effect on the corrosion continuance of the dynamic recrystallization high-angle (RHA) grain boundaries can improve the corrosion resistance of the RHA grain boundaries.

Stress corrosion cracking of aluminum alloys from the viewpoint of intergranular corrosion sensitivity and hydrogen embrittlement

Stress corrosion cracking of aluminum alloys from the viewpoint of intergranular corrosion sensitivity and hydrogen embrittlement

New Findings on Intergranular Corrosion Mechanism of 445J2 Ultra-Pure Ferritic Stainless Steel

A criterion for characterizing the intergranular corrosion sensitivity of 445J2 ultra-pure ferritic stainless steel was established using microstructure analysis and electrochemical impedance spectroscopy (EIS). The differences in the characterization results for the intergranular corrosion sensitivity of 445J2 stainless steel by EIS and the double loop-electrochemical potentiokinetic reactivation test were analyzed. The Mo-rich intermetallic compound did not cause depleted chromium zones in the sensitization temperature range of 500°C to 700°C but caused a surrounding elastic stress field. It was determined that the intergranular corrosion in 445J2 is due to the elastic stress field caused by the precipitated phase.

Effect of Two-Stage Aging on Microstructure and Properties of Al-Mg-Si Alloys

The effects of two-stage aging on the microstructures, tensile properties and intergranular corrosion (IGC) sensitivity of Al-Mg-Si alloys were studied by tensile testing and IGC experiments and transmission electron microscope (TEM). The results show that the two-stage aging (180°C, 2h+160°C, 120h) can reduce the IGC sensitivity without decrease the tensile properties. The grain is distributed with high-density β′′ phases, and the grain boundary phases are spherical and intermittently distributed. The formation of the microstructure characteristic is due to the lower re-aging temperature, which results in a decline differences in the diffusion rate between the matrix and grain boundaries. As a result, the pre-precipitated phase can maintain a better strengthening effects due to the slower growth rate. The pre-precipitated phase of the grain boundary presents a spherical and intermittent distribution due to the fast coarsening speed.

Effect of nitrogen protection on weld metal microstructure and intergranular behavior of S32101 duplex stainless steel 15 m water depth hyperbaric laser underwater welding

In this study, 16-mm-thick S32101 duplex stainless steel were welded using hyperbaric underwater laser welding system in 0.15 MPa. The misorientation angle distribution of grain boundaries in the weld metal was analyzed using the electron backscatter diffraction technique. The ionic currents near the surface of metallography were measured by the Scanning Vibrating Electrode Technique (SVET) and performed to evaluate the intergranular corrosion (IGC) resistance based on corrosion current density. The volume fractions of ferrite and austenite and the grain boundary misorientation angle affect the IGC sensitivity of the welded joints. The relationship between the grain boundary misorientation angle of the austenite and corrosion resistance was analyzed. When the weld metal was shielded with nitrogen, and the volume fraction of austenite and the frequency of Σ3 coincidence site lattice boundary in the weld was increased. The misorientation angle distribution in the austenite and the frequency of Σ3 coincidence site lattice boundary influence the IGC resistance of the welded joints.

Effect of low-temperature cooling on corrosion properties of laser welding Hastelloy C-276/304 stainless steel with filler wire

To suppress the weld defects and improve corrosion resistance of laser welded joints, the low-temperature cooling was applied to assist laser welding Hastelloy C-276/304 stainless steel with filler wire. And the different low-temperature cooling (-5 °C, 5 °C, 20 °C) were selected for experimental research. Results show that adding low-temperature cooling can increase the cooling rate and solidification rate of weld. And the temperature gradient grows with the increase of solidification rate near the fusion line of weld. Consequently, the content of precipitated phase decreases from 1.75% to 0.71%, reducing by nearly 59.0%. The increase of temperature gradient can reduce the unmixed zone, which decreases from 22.1 μm to 11.4 μm, reducing by nearly 48.0%. At the same time the contents of corrosion-resistant elements and the proportion of grain boundaries with small angles increase in the laser weld with low-temperature cooling. As the cooling temperature drops, the effect of microstructure optimization of weld is enhanced. Finally, the corrosion properties of welded joints are obviously improved with the temperature decrease. The corrosion potential of welded joints increases by 24.3%. The corrosion current density of welded joints reduces by 54.3%. The intergranular corrosion sensitivity of welded joints reduces by 76.5%.

Anisotropic Inter-granular Corrosion Behaviors and Microstructures of AlMgSiCu Alloy Sheets Made by Thermal–Mechanical Treatments

This study investigates the microstructure and local corrosion behavior of an Al–Mg–Si–Cu alloy, which has been subjected to cold-rolling with different deformation strain ratios (DSRs) and followed by artificial aging. Accelerated corrosion tests show that peak-aged samples with a small DSR (5–10%) are sensitive to inter-granular corrosion (IGC) along both the normal and rolling directions. When the DSR increases to medium strength (20–40%), IGC sensitivity decreases along both directions and corrosion propagates anisotropically. When the DSR is 60–80%, IGC sensitivity along the normal direction continues to decrease, but increases along the rolling direction, indicating pronounced corrosion anisotropy. Microstructural characterization reveals the decreased IGC sensitivity is mainly attributed to a reduction in element segregation at high-angle grain boundaries and the kinked and discontinuous grain boundary corrosion paths. The increased IGC sensitivity along the rolling direction could be related to the significantly flattened grains.

Ausztenites korrózióálló acél szemcsehatármenti korrózióra való hajlamának elemzése fizikai szimulációval

Mint ismeretes, az ausztenites korrózióálló acélok, ha azok karbontartalma meghaladja a 0,03-0,04%-ot, nagyobb hőmérsékletről lassan hűtve, vagy 500 - 900 ˚C hőmérséklet közben hőn tartva, nem lesznek homogén szövetszerkezetűek. Az ausztenit mellet számos intermetallikus vegyület válik ki, amelyek közül a szemcsehatármenti korrózió kialakulása szempontjából a M23C6 karbid kiválása a meghatározó. A kiváló nagy krómtartalmú (kb. 65%) fázis környezetében az ausztenit Cr tartalma 10,5% alá csökkenhet, így az acél kristályközi korrózióra hajlamossá válhat. A szemcsehatármenti korrózióra hajlamos ausztenites korrózióálló acélok esetén a hegesztési hőfolyamat hatására is kialakulhat a nem kívánt kiválás. Az egyes ausztenites korrózióálló acélok érzékenységének jellemzése érdekében ún. szenzibilizációs diagramokat célszerű meghatározni, amelyeknél a hőntartás hőmérséklete és ideje függvényében a karbidok elhelyezkedési, előfordulási területeit jelenítik meg. Tekintettel arra, hogy a hegesztés hőciklusa jelentősen különbözik az állandó hőmérsékletű kezelésnél alkalmazottól, a szemcsehatármenti korróziós hajlamot a hegesztési hőfolyamat paramétereinek függvényében célszerű elemezni. Jelen kutatómunkában fizikai szimulációval előállított hegesztési hőciklus(ok)nak kitett próbatesteken (X5CrNi18-10, 1.4301) végeztünk kísérleteket egy Gleeble 3500 típusú berendezésen, amelynek során különböző maximális hőmérsékleteket létrehozva, változó lehűlési profilokat vizsgáltunk. A vizsgálati eredmények felhasználásával különválasztottunk néhány olyan hegesztési hőciklust, amelyek alkalmazása esetén bekövetkezhet szemcsehatármenti korrózió, illetve az elkerülhető a vizsgált ausztenites alapanyagon.

Influence of Minor Zn Addition on Precipitation Behavior and Intergranular Corrosion Properties of Al-Mg-Si Alloy.

The effect of 0.2 wt.% Zn addition on microstructure, age hardening and intergranular corrosion (IGC) properties of Al-Mg-Si alloy were investigated by scanning electron microscope, transmission electron microscope, hardness testing, and electrochemistry testing. The results showed that the addition of Zn can accelerate the transformation of GP zones into β″, and make the intragranular precipitates become smaller and with higher density. This is beneficial to the precipitation strengthening of the alloy, leading to obtaining higher hardness and enhancing the age hardening response. The peak hardness of the alloy with the addition of Zn is 125.8 HV which means increasing the hardness by 12.7 HV, compared with the alloy without Zn. However, the addition of Zn makes the precipitate-free zone (PFZ) of the alloy wider, and coarsens the grain boundary precipitates slightly, which result in the reduction of IGC resistance of Al-Mg-Si alloy. The maximum corrosion depth of the Zn-containing alloy is 121.3 μm in the peak age condition, which is 35.7 μm deeper than the alloy without Zn. The result of the potentiodynamic polarization curves also demonstrated the increase of IGC sensitivity. The corrosion current density of the alloy with added Zn is 0.595 μA/cm2 in the peak age condition, while that for the alloy without Zn is 0.199 μA/cm2.

Change of Intergranular Corrosion Sensitivity of HR3C Steel Under the Condition of 700°C Aging

This paper studies the change of intergranular corrosion sensitivity of HR3C steel under the condition of 700°C aging by using the scanning electron microscope, energy disperse spectroscopy (EDS), and double-loop Electrochemical potentiokinetic reactivation (EPR) method. The results show that the main reason for the intergranular corrosion of HR3C steel after aging treatment is the precipitation of M23C6 along the grain boundary. The morphology and size of M23C6 also matters in this regard. At the same time, M23C6 precipitation also causes corrosion of Cr around it. M23C6 precipitates at the fastest speed at the beginning of aging, which leads to the rapid increase of intergranular corrosion sensitivity. As aging continues, M23C6 precipitation becomes gradually stable. After the precipitation of large-sized isolated granules, the intergranular corrosion sensitivity of HR3C steel decreases rapidly and maintains at a low level.

Non-isothermal Ageing of an Al-Mg-Si Alloy for Enhanced Anticorrosion Performance

The effects of different heat treatment processes on the comprehensive properties of Al-Mg-Si were investigated. The results show that the microstructures changes by T6, T73 and non-isothermal aging (NIA) lead to different hardness and electrochemical properties. The β” strengthening phase of T6 alloy has fine dispersion, uniform size and maximum sensitivity to intergranular corrosion (IGC). The hardness of alloy crystal is the lowest after T73 treatment. The number of β” phases in the crystals of the NIA-treated alloy is the largest, but there is a small amount of coarsened β” phase, and the grain boundary precipitates are intermittently distributed. The IGC sensitivity is the lowest. The NIA-treated alloy has both high strength and good corrosion resistance, which is related to the formation of a large amount of precipitates in the crystal at low temperatures and the growth and coarsening of intergranular precipitates at high temperatures.

Intergranular Corrosion Sensitivity of Welded Joint of Super304H at High Temperature

AbstractThis paper investigated the effect of sensitization time (0h,5h,15h,30h)on intergranular corrosion sensitivity of welded joints of Super304H stainless steel at 650°C by electrochemical impedance spectroscopy (EIS), electrochemical potentiodynamic reactivation (EPR) method and scanning electron microscopy (SEM). EPR results showed that with the increase of sensitization time, the value of reactivation rate Ra increased. Electrochmical impedance spectra of welded joint of super304H for different sensitization time exhibited the similar characteristics. The fitted results showed that the values of Rf decreased with the increase of sensitization time.