Intergranular Corrosion Test Research Articles

Evaluation of Passivation Process for Stainless Steel Hypotubes Used in Coronary Angioplasty Technique

In the manufacturing of hypotubes for coronary applications, austenitic steels of types 304, 304, or 316 L are being used. The manufacturing process involves bending steel strips into tubes and the continuous longitudinal welding of the tubes. Manufacturing also includes heat treatments and stretching operations to achieve an external/internal diameter of 0.35/0.23 mm, with a tolerance of +/− 0.01 mm. Austenitic steels are sensitive to localized corrosion (pitting, crevice, and intergranular) that results from the welding process and various heat treatments. An extremely important step is the cleaning and the internal and external passivation of the hypotube surface. During patient interventions, there is a high risk of metal cations being released in contact with human blood. The aim of this study was to evaluate the state of passivation and corrosion resistance by using electrochemical methods and specific intergranular corrosion tests (the Strauss test). There were difficulties in passivating the hypotubes and assessing the corrosion phenomena in the interior of the tubes. Assessments were made by plotting the open circuit potential curves and exploring the polarization curves in the Tafel domain range of −50 mV vs. Ecorr (redox potential) and +150 mV vs. saturated calomel electrode (SCE, reference micro-electrode) for both the external and the internal surfaces of the hypotubes. The tested hypotubes did not exhibit intergranular corrosion, as mass losses were low and, in general, close to the limit of the analytical balance. Electrochemical techniques made the differentiation of the passivation state of the tested hypotubes possible. The measured currents were of the order of nano–pico amperes, and the quantities of electrical charges consumed for corrosion were of the order of micro–nano coulombs.

Corrosive Behaviour of Friction Stir Al Alloy Welding Technique: A Review

Friction stir welding (FSW) is a technique under which solid state joining process principal working upon the materials for infusing strength. As reported by myriad scholars FSW emphatically used in automobiles, air craft structures, ship building etc. With priority to consume alloys used aluminum as base metal. Due to their cost effectiveness and lighter in weight. We discussed alloys of 2xxx, 5xxx, 6xxx, 7xxx series to ascertain the corrosion nature of prime material. Aluminums may be heat treated or non-heat treated so we discussed the impact of various corrosive techniques for strengthening the alloys. This article elaborate about the corrosion behavior of the material over HAZ, NZ, TMAZ regions of welded part and ascertain the various process parameters under intergranular corrosion testing(ICG) & Electrochemical impedance spectroscopy (EIS) technique under varying circumstances. Purpose of this paper is to enhance the fundamental skill of researchers in future for effectively dealt with the improvement of Aluminums alloys.

Effects of re-solution and re-aging treatment on mechanical property, corrosion resistance and electrochemical behavior of 2196 Al-Cu-Li alloy

The effects of re-solution (RST) and re-aging (RA) treatment on the mechanical property, microstructure, corrosion resistance and electrochemical behavior of 2196 Al-Cu-Li alloy were investigated by tensile testing, conductivity testing, intergranular corrosion and electrochemical corrosion testing. The results show that RST and RA treatment can improve the corrosion resistance without sacrificing the strength compared to T6 temper. The aging precipitation process is reversible, and the number and distribution of δ’, T1 and θ’ precipitates can be effectively regulated by the RA treatment, so that the strength of the alloy approximately reaches the level of T6 temper and the ductility is improved. The corrosion mode of the alloy changed from pitting into intergranular corrosion during RST and RA treatment. The coarsening and discontinuous distribution of grain boundary precipitates as well as the increase of precipitate-free zone (PFZ) width inhibit the generation and propagation of stress corrosion cracking and thereby improve the corrosion resistance of the alloy. The increase of Cu content in grain boundary reduces the electrochemical corrosion sensitivity of the alloy. The optimal process parameters of RST and RA treatment for 2196 Al-Cu-Li alloy are finally determined to be 515 °C for 90 min and 170 °C for 24 h.

Microstructural and intergranular corrosion properties of Inconel 625 superalloys fabricated using wire arc additive manufacturing

Inconel 625 superalloy samples were fabricated using wire arc additive manufacturing (WAAM). The phase composition, microstructure, anti-corrosion, and mechanical properties of the Inconel 625 WAAM samples were analyzed. The microstructure of the Inconel 625 WAAM alloy showed good forming quality, no defects, and good metallurgical bonding within the specimens. The metallographic structure exhibited primarily γ-Ni and granular precipitated phases; the average microhardness of the transverse and longitudinal cross-sections of the sample was 243.5 and 243.3 HV0.1, respectively. Yield and tensile strength as well as elongation, decrease in area, and the room-temperature impact values of this alloy were equal to 450 and 736 MPa, 38% and 52%, and 152 J, respectively. The intergranular corrosion test results indicated that the average corrosion rate of the sample is 0.609 mm/year, indicating excellent resistance to intergranular corrosion.

Comparing intergranular corrosion in Al‐Mg‐Si‐Cu alloys with and without α‐Al(Fe,Mn,Cu)Si particles

AbstractIn this study, a model alloy without Fe and Mn additions, is compared with a commercial AA6005 alloy to further understand how the α‐Al(Fe,Mn,Cu)Si particles affect intergranular corrosion (IGC) behaviour. Both alloys were subjected to an accelerated IGC test for durations ranging from 1 to 120 h. Microstructures were studied using scanning and transmission electron microscopy, and electron backscatter diffraction. The presence of α‐Al(Fe,Mn,Cu)Si particles yields significantly more uniform IGC attacks and higher corrosion rates. However, the maximum depth of IGC attacks reaches similar values after ~24 h of exposure. This is attributed to the formation of Cu‐rich particles along the grain boundaries during the corrosion process, which further catalyses the cathodic reactions.

Mechanical Investigations of ASTM A36 Welded Steels with Stainless Steel Cladding

The in-service life of ASTM A36 welded steel pipes in power plants is often shortened by ash corrosion. During the heating condition, the ash deposition on the welded steel pipes gradually reduces the thickness of the pipes, thus, reducing the lifetime. Instead of replacing the pipes with new ones, the cost could be significantly reduced if the lifetime could be further extended. Weld cladding was the method selected in this study to temporarily extend the service life of welded pipes. This paper performed the mechanical investigations of A36—A36 welded steel plates after coating the surfaces with 309L stainless steel with a cladding method. The residual stress was also tested to observe the internal stresses developed during the welding processes of A36—A36 specimens. The comparison between the coated and non-coated surfaces of welded steels was performed by using the tensile tests (at room and elevated temperatures), corrosion (pitting corrosion, intergranular corrosion, and weight-loss corrosion) tests, and wear (shot blasting) tests. The life-extension of both coatings was evaluated based on the tensile tests and the corrosion and wear tests provided the qualitative evaluations of the coating performance. The results showed that surfaces coated by cladding could be used to temporarily extend the life of ASTM A36 welded steel under the studied conditions.

Suppression of intergranular corrosion by surface grain boundary engineering of 304 austenitic stainless steel using laser peening plus annealing

Grain boundary engineering (GBE) has a high potential to suppress intergranular degradation and improve weld properties. Thermomechanical processing is typically used to optimize grain boundary character distributions (GBCDs) for the GBE of face-centered cubic materials with low stacking fault energy. Pre-straining plus annealing has achieved the optimal GBCD for GBE of austenitic stainless steels. Typically, cold rolling is used for pre-straining, but is not suitable for products with complex shapes. Laser peening can introduce strain locally and flexibly, even on complex parts. Therefore, this study attempted to apply laser peening as a pre-straining method during the thermomechanical processing. Several sets of process parameters during laser peening were selected to introduce suitable pre-strain into the surface of a 304 steel specimen based on previous GBE studies focusing on cold rolling plus annealing. Annealing at 1260 K for 48 h following laser peening led to an optimal GBCD with over 80 % frequency for coincidence site lattice boundaries and disconnected random boundaries. An intergranular corrosion test revealed that the laser-peened and annealed 304 steel with an optimal GBCD exhibits excellent intergranular corrosion resistance, which is far greater than that of an as-received sample and comparable to that of a cold-rolled and annealed sample.

Response of mechanical properties and corrosion behavior of Al–Zn–Mg alloy treated by aging and annealing: A comparative study

The high strength Al–Zn–Mg plates were processed by combing the hot extrusion and cold rolling. Then, both the artificial aging and annealing were conducted to make a comparative study on the microstructure, mechanical properties, and corrosion resistance. The aged samples were composed of near-equiaxed grains attributed from the static recrystallization during solution process, and owned the main textures of Cube, Goss, Copper, S, and Brass. The precipitate followed the sequence of SSS → GP zone → η′ phase → η phase. With the increase of aging time, the grain boundary precipitations (GBPs) became coarse and discontinuous, and the width of precipitate free zones (PFZs) also increased. In annealed samples, the coarse and elongated grains were finally formed, and the volume fraction of recrystallization textures increased with the extension of annealing time. Moreover, the density of dislocations and the number of MgZn2 phase were both reduced during annealing. The tensile strength along 0° with rolling direction was always the highest in all aged and annealed samples, and the elongation achieved the highest values along 45°. Long-time aging slightly improved the planar anisotropy, while long-time annealing greatly improved the planar anisotropy. The peak aged sample showed a ductility loss of 21.96% during the slow strain rate test in 3.5 wt% NaCl, and a maximum depth of 214.59 μm in intergranular corrosion test. Compared to the annealed sample, the aged one exhibited the worse corrosion resistance due to the wide PFZs and continuously distributed GBPs.

Effect of the Zn/Mg Ratio on Microstructures, Mechanical Properties and Corrosion Performances of Al-Zn-Mg Alloys

The effect of the Zn/Mg ratio on microstructures, mechanical properties and corrosion performances of Al-Zn-Mg alloys was studied. Microstructures were characterized using the optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). Tensile tests, intergranular corrosion (IGC) and stress corrosion cracking (SCC) tests were conducted to study the properties. Microstructures results indicated that with the decrease of the Zn/Mg ratio, the recrystallization proportion and the fraction of second phase decreased, while the size of η’ (MgZn2) phases in grain interior also significantly decreased. The number density of η’ phases in grain interior increased and grain boundary precipitates developed discontinuous distribution with the decrease of the Zn/Mg ratio. These microstructures contributed to the significant improvement of the strength and corrosion resistance. The tensile strength and yield strength increased by 34.1% and 47.4%, respectively, with the Zn/Mg ratio decreased from 11.4 to 6.1. Calculating results indicated that the enhancement of strength mainly contributed from the solid-solution strengthening, grain-boundary strengthening and precipitation strengthening. The intergranular corrosion degree was greatly relieved and the stress corrosion sensitivity index decreased from 0.031 to 0.007 with the Zn/Mg ratio decreased from 11.4 to 6.1.

Study on Application Performance of Instrument Valve Body Formed by Selective Laser Melting for Nuclear Power Plant

A 316L stainless steel instrument valve body which with complex internal flow passage and used for primary loop flow measurement in pressurized power plant along with test specimen were printed by selective laser melting. The optical metallography of specimen showed the microstructure transform to be uniform after heat treatment state. The residual stress test was tested on three different position on the valve body after heat treatment. The results showed that the valve body mainly had a surface residual compressive stress, and the max main stress was in a range of-367.27MPa to 34.97MPa which get higher along the building direction. Then the application performance of intergranular corrosion test and hydraulic test on the valve body showed a good performance and the result could meet the acceptance requirements of the construction rule.

Insight into the microstructural features and corrosion properties of wire arc additive manufactured super duplex stainless steel (ER2594)

This work investigates the understanding between microstructure and corrosion behaviour of SDSS 2594 wall component fabricated using gas metal arc welding (GMAW) based wire arc additive manufacturing (WAAM) process, with the help of optical micrographs and electrochemical corrosion tests. Potentiodynamic polarization tests and Electrochemical impedance spectroscopy (EIS) analysis in 3.5% NaCl solution revealed excellent pitting resistance while the corrosion rate ranged between 1.51 and 1.61 mils per year (mpy) with pitting resistance equivalent number (PREN) > 40. The intergranular corrosion (IGC) test results confirmed the absence of sensitization and highlights that the formation of passive film is compact for corrosive environments.

A study on corrosion behavior of stainless steel dissimilar alloy weld joints (321 & 347)

In this work dissimilar weld is obtained between SS 321 and SS 347 through robot guided MIG welding process. The Weldments are subjected to intergranular Corrosion test as per ASTM A262 and studied. Particularly considering the applications in wide range such as chemical storage, exhaust manifolds of automobiles and aircraft, where the surfaces are subjected to corrosive environment is taken for investigation. The specimens were welded with two different electrode wires ER 321 and ER 347. The results found that at 140A welding current and with ER347 there are no intergranular cracks and fissures found. The ER 347 is found to be the best suited electrode when compared to ER321 for welding these dissimilar joints.

Effect of Mg Content on the Microstructure and Corrosion Properties of Al-Cu-Mn Alloy

In this paper, the effect of Mg content on the microstructure and properties of Al-Cu-Mn alloy was investigated. The microstructures and the mechanical properties of the alloys were studied by scanning electron microscopy and transmission electron microscopy, and Vickers hardness measurement, respectively. Furthermore, the effect of Mg content on the corrosion resistance of the alloys was explored by exfoliation corrosion test, intergranular corrosion test, and electrochemical techniques. The results show that the overall properties of Al-Cu-Mn alloy with 0.1 wt.% Mg are superior to other alloys. Specifically, the Vickers hardness of this alloy reaches 111.45 HV. The grating of exfoliation corrosion is EA, and the intergranular corrosion depth is 30.2 μm. It is believed that the improved mechanical properties and corrosion resistance of the Al-Cu-Mn alloy with 0.1 wt.% Mg result from the S phase formed in the alloy and the highly dispersive distribution of the θ phase.

Crystallographic Evaluation of Susceptibility to Intergranular Corrosion in Austenitic Stainless Steel with Various Degrees of Sensitization.

This study investigated the susceptibility to intergranular corrosion (IGC) in austenitic stainless steel with various degrees of sensitization (DOSs) from a microstructural viewpoint based on the coincidence site lattice (CSL) model. IGC testing was conducted using oxalic acid and type 304 stainless steel specimens with electrochemical potentiokinetic reactivation (EPR) ratios that varied from 3 to 30%. As a measure of IGC susceptibility, the width of the corroded groove was used. The relationship between IGC susceptibility, grain boundaries (GB) structure, and EPR ratio of the specimens was evaluated. As a result, the IGC susceptibility cannot be characterized using the Σ value, irrespective of the DOS of the specimen. The IGC susceptibility increases with increasing unit cell area of CSL boundaries, which is a measure of the stability of the CSL boundaries, and then levels off. The relationship between the IGC susceptibility and unit cell area is sigmoidal, irrespective of the DOS of the specimen. The sigmoid curve shifts rightward and the upper bound of IGC susceptibility decreases with decreasing DOS of the specimen.

Effect of ageing temperature on microstructure, mechanical property and corrosion behavior of aluminum alloy 7085

The influence of ageing temperatures on mechanical properties, corrosion behavior and precipitation features of aluminum alloy 7085 have been investigated by using tensile testing, intergranular corrosion tests, polarization curve measurements and transmission electron microscopy (TEM) observations. The results show that the precipitate sequence of aluminum alloy 7085 is different at different ageing temperatures. GP II is the main strengthening precipitate in the alloy peak aged at 90 °C, while η′ contributes most to the strength of the alloy peak aged at 150 °C. Similar ultimate yield strength can be obtained under either peak ageing conditions, but the work-hardenability at 90 °C is much better than that at 150 °C due to the predominance of GP II zones. Alloy 7085 peak aged at 150 °C shows better corrosion resistance than at 90 °C.

Influence of heat treatment on corrosion behavior of rare earth element Sc modified Al-Mg alloy processed by selective laser melting

In this study, electrochemical measurements, intergranular corrosion (IGC) resistance tests, X-ray photoelectron spectroscopy (XPS) and microstructure analyses were performed to study the influence of heat treatment on the corrosion behavior of SLM produced Al-Mg-Sc-Zr alloy. Electrochemical results and IGC tests revealed that the SLM-fabricated Al-Mg-Sc-Zr specimen possessed a superior corrosion resistance and a better IGC resistance than the heat-treated specimen. For both specimens, pitting was the main corrosion form and massive pits were formed along molten pool boundaries. Different corrosion morphologies were observed inside the molten pool for SLM-fabricated and heat-treated Al-Mg-Sc-Zr specimens after corrosion tests, where pits were generated along grain boundaries for the heat-treated specimen while no pits were found inside the molten pool for the SLM-fabricated specimen. XRD and TEM analyses further revealed that the unfavorable corrosion resistance of the heat-treated specimen relates to the formation and coarsening of Al3(Sc,Zr) precipitations during heat treatment. The massive pits formed along molten pool boundaries were related to the refined grain size and aggregation of precipitations, and the different corrosion morphologies inside the molten pool were attributed to secondary Al3(Sc,Zr) precipitations generated at grain boundaries during aging process.

Effects of heat input and cooling rate during welding on intergranular corrosion behavior of high nitrogen austenitic stainless steel welded joints

Intergranular corrosion of welded joints using multi-strand winded welding wire was investigated using the double loop electrochemical potentiokinetic reactivation (DL-EPR) tests, intergranular corrosion tests and scanning Kelvin probe force microscopy (SKPFM) tests. The results revealed welded joint in high heat input and low cooling rate shows the highest DOS value, and undergoes the most important weight loss during intergranular corrosion tests. While welded joint in low heat input and cooling rate has the highest corrosion resistance. SKPFM also indicated that welded joint in the low cooling rate and heat input presents low potential and is not easy for electrochemical reaction.

Effect of pre-aging deformation on the intergranular corrosion resistance of 6000 series aluminium alloys

Aluminium alloys in the 6000 series may become susceptible to intergranular corrosion (IGC) by unfavourable thermomechanical processing in combination with presence of Cu and a low Mg/Si ratio. The IGC susceptibility has been related to the segregation of Cu during artificial ageing to form a nearly continuous Cu film along the grain boundaries with an anodic solute depleted zone adjacent to it. In this work, extruded alloys 6005 and C28 as well as two variants of 6016 automotive sheet were subjected to various degrees of deformation by rolling or stretching before artificial aging. Accelerated IGC testing showed that pre-deformation significantly improved the IGC resistance of the Cu containing extruded alloys, while no improvement was observed for the 6016 sheet materials containing < 0.01 wt% Cu. High resolution scanning transmission electron microscopy (STEM) of pre-deformed 6005 alloy showed precipitation of Cu-containing Q' phase on dislocations. As a result, the amount of Cu available for diffusion to the grain boundaries is reduced, which might explain why a beneficial effect of pre-deformation on the IGC resistance was observed only for the Cu-containing materials.

Effect of Heat Treatment on the Phase Composition and Corrosion Resistance of 321 SS Welded Joints Produced by a Defocused Laser Beam.

The effect of heat treatment of welded joints made of steel 321 on corrosion resistance, phase composition, residual stresses, and distribution of alloying elements was studied using optical microscope (OM) and scanning electron microscope (SEM), electron dispersive spectroscopy (EDS), X-ray diffraction (XRD), and intergranular corrosion testing (IGC). Samples previously obtained by the authors using defocused laser beam, which led to the formation of directionally crystallized austenite with lathy and skeletal δ-ferrite, were investigated. Based on X-ray diffraction studies in the base metal, the maximum number of peaks of various phases was presented, which decreased after exposure to the heating effect of the welding process and subsequent heat treatment. The distribution of alloying elements, in particular, Ti and Si, was significantly affected by heat treatment depending on the regimes. A spot chemical analysis showed that the nickel content differs in δ-ferrite and austenite by 1.5%–2% whereas the chromium content in these phases is not significantly different. Tests have shown that all samples have high resistance to intergranular corrosion, which can be explained by the insufficient dissolution of titanium carbides in austenite and the absence of chromium carbides formation along austenite grain boundaries, due to high cooling rates when welding by a defocused laser beam, and as a result, the high δ-ferrite content in which chromium dissolves.

Effects of non-isothermal aging on mechanical properties, corrosion behavior and microstructures of Al-Cu-Mg-Si alloy

Effects of non-isothermal aging (NIA) treatments on the mechanical properties, intergranular corrosion (IGC) and microstructures of Al-Cu-Mg-Si alloy were investigated by tensile test, intergranular corrosion test, electrochemical analysis, optical microscopy and transmission electron microscopy. Compared with isothermal peak-aging (T6) treatment, the NIA treatments effectively improve the intergranular corrosion resistance by narrowing precipitation free zones (PFZ) and breaking the continuous distribution of precipitates on the grain boundaries. Under NIA treatments, with the increase of heating rate, the width of PFZ decreases induces the improvement of intergranular corrosion resistance. The mechanical properties of NIA treatment could be enhanced by adjusting the heating rate. The tensile strength and yield strength after NIA treatment with a heating rate of 20 °C/h are increased 1.5% and 5.8% than that after T6 treatment, respectively, which is ascribed to finer intra-grain precipitates. Reasonably, the mechanical properties and intergranular corrosion resistance could be improved simultaneously by adjusting the heating rate of NIA treatments.