Intergranular Corrosion Resistance Research Articles

Understanding the effect of decreasing C contents and increasing solid-solution time on intergranular corrosion resistance of 304 austenitic stainless steel

The purpose of this study is to investigate the intergranular corrosion resistance mechanism of 304 austenitic stainless steel treated by decreasing C contents and increasing the solid-solution treatment time. The findings indicate the effect of decreasing C contents and increasing the solid-solution treatment time effectively limits the intergranular corrosion behavior of the steel within an acceptable range (degree of sensitization, DOS values < 1). On the one hand, reducing the carbon content in the 304 austenitic stainless steel leads to insufficient levels of carbon that is necessary to reach the critical value for Cr-carbide nucleation, which decreases the occurrence of Cr-depleted zones. In comparison, the intergranular corrosion tendency of 304 austenitic stainless steel decreases at higher solid-solution temperatures and for longer treatment times, and its main purpose is to reduce the occurrence of large-sized Cr-carbide and its pinning effect on the grain boundaries. Moreover, the reduction in grain boundaries due to the grain growth further constrains the intergranular corrosion behavior of 304 austenitic stainless steel, which provides strong support for further optimizing the process conditions and reducing the failure caused by intergranular corrosion.

Effect of final rolling temperature on microstructure and intergranular corrosion resistance of an Al–Cu–Mg–Ag alloy

Connection of microstructure with corrosion properties of an Al-3.62Cu-0.9Mg-0.45Ag alloy in natural aging (NA) state and peak aging (PA) state at different final rolling temperatures (20 °C, 180 °C and 280 °C) are studied by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), X-ray diffraction (XRD), texture and electrochemical analysis. The results show that the deformation texture and recrystallization texture of T280-NA alloy account for the largest percentage with the largest degree of recrystallization. With the increase of final rolling temperature, the proportion of low angle grain boundaries (LAGBs) of NA alloy increases, the diameter, thickness and volume fraction of Ω phase in PA alloy decrease, and the grain boundary precipitates (GBPs) are gradually transformed from discontinuous distribution to continuous distribution. The grain boundary precipitates are also found to be consist of alternating S and θ phases and the width of precipitation free zones (PFZs) is essentially independent of final rolling temperature. The intergranular corrosion (IGC) resistance of T280-NA alloy and T20-PA alloy is the best, which is a result of the combined effect of GBPs, texture and grain boundary properties. In addition, this result is verified in this paper by studying the electrochemical properties of the alloy.

Effect of Retrogression with Different Cooling Ways on the Microstructure and Properties of T'/η' Strengthened Al-Zn-Mg-Cu Alloys.

Retrogression and re-aging (RRA) treatment has been proven to effectively overcome the trade-off between strength and corrosion resistance. Current research focuses on the heating rate, temperature, and holding time of retrogression treatment while ignoring the retrogression cooling ways. In this paper, the effects of RRA treatment with different retrogression cooling ways on the microstructure and properties of newly developed T'/η' strengthened Al-Zn-Mg-Cu alloys were investigated by performing tests on mechanical properties, intergranular corrosion (IGC) resistance, and electrochemical corrosion behavior. The results show that the mechanical properties of samples subject to RRA treatment with water-quenching retrogression (ultimate tensile strength, yield strength, and elongation of 419.2 MPa, 370.2 MPa, and 15.9, respectively) are better than those of air-cooled and furnace-cooled samples. The corrosion resistance of water-quenching (IGC depth of 162.2 μm, corrosion current density of 0.833 × 10-5 A/cm2) and furnace-cooled samples (IGC depth of 123.7 μm, corrosion current density of 0.712 × 10-5 A/cm2) is better than that of air-cooled samples. Microstructure characterization reveals that the effect of the retrogression cooling rate on mechanical properties is related to the size of T'/η' precipitates with grains as well as the proportion of T' and η', while the difference in corrosion resistance depends on the continuity of grain boundary precipitates (GBPs). With mechanical properties, corrosion resistance, and time cost taken into consideration, it is appropriate to select water quenching for retrogression. These findings offer valuable insights for further design to achieve superior performance in various applications.

Improving mechanical property and corrosion resistance of high electrical conductivity Al-Ce-Sc-Y and Al-Mg-Si-Ce-Sc-Y alloys by laser shock peening

The high electrical conductivity Al-Ce-Sc-Y and Al-Mg-Si-Ce-Sc-Y alloys were used to study the effects of laser shock peening on their mechanical property, pitting and intergranular corrosion resistance. The strength and elongation of the alloys were improved simultaneously at the expense of very low electrical conductivity after laser shock peening due to the gradient structure and residual compressive stress. After two side laser shock peening, the strength and elongation of Al-Ce-Sc-Y and Al-Mg-Si-Ce-Sc-Y alloys increased to 231 ± 3 MPa/16.2 ± 0.2 % and 359 ± 3 MPa/17.1 ± 0.3 %, respectively. The samples with two surface states were used to study the corrosion behaviors. The number and depth of corrosion pits can be significantly reduced by laser shock peening and the crystallographic corrosion morphology exists in the corrosion pits. After two side laser shock peening with polished surface, the intergranular corrosion depth of Al-Mg-Si-Ce-Sc-Y alloy can reach the minimum and the intergranular corrosion cracks are much finer at the same depth. The Al-Ce-Sc-Y alloy had no tendency of intergranular corrosion, but the unpolished surface was prone to form the deep corrosion pits rather than occurred uniform corrosion. According to the microstructure analysis, the corrosion mechanism of pitting and intergranular corrosion was revealed.

Inhibition of the second phase precipitation and improvement of intergranular corrosion resistance by boron segregation at the grain boundary of S31254 superaustenitic stainless steel

The inhibition of Mo segregation and phase precipitation is vital for improving the hot workability and corrosion resistance of superaustentic stainless steels (SASS). The boron non-equilibrium segregation of S31254 SASS was implemented through solid solution, air cooling, and diffusion at low-temperature treatment (SADT). The precipitation process and intergranular corrosion (IGC) of S31254 SASS with various boron distributions were researched at a sensitive temperature. The second phases were observed and identified by SEM and TEM. IGC susceptibility was evaluated by double-loop potentiodynamic reactivation (DL-EPR) measurements. The SADT treatment promoted more segregation of B at the grain boundary, leading to lower amounts of grain boundary precipitation before aging for 6 h. The decrease of σ phases in B-regulated samples enhances the IGC resistance, compared with the samples without B addition specimens.

Evolution of Mechanical Properties and Corrosion Resistance of Al-Zn-Mg Alloy with Different Numbers of Flame Rectification at 350°C

This paper investigated the microstructure, tensile properties, intergranular corrosion resistance and exfoliation corrosion resistance of Al-4.5Zn-1.5Mg (wt.%) alloy after undergoing different numbers of flame rectification at 350°C. The results showed that in the flame correction area, the mechanical properties of Al-4.5Zn-1.5Mg(wt.%) alloy with two times of flame correction is the best. The maximum tensile strength and elongation of Al-4.5Zn-1.5Mg(wt.%) alloy inside the region of flame correction are 387MPa and 26.37% respectively. The flame rectification accelerated the corrosion susceptibility of Al-4.5Zn-1.5Mg (wt.%) alloy. The maximum intergranular corrosion depth is detected with the value of 105μm after one time of FR. The corrosion property of Al-4.5Zn-1.5Mg(wt.%) alloy is mainly related to the formation of galvanic couple. The uneven distribution of the second phase particles of Al-4.5Zn-1.5Mg(wt.%) alloys results in different corrosion potentials at grain boundaries and within grains, leading to galvanic corrosion.

Machine Learning-Based Prediction of Intergranular Corrosion Resistance in Austenitic Stainless Steels Exposed to Various Heat Treatments

Machine Learning-Based Prediction of Intergranular Corrosion Resistance in Austenitic Stainless Steels Exposed to Various Heat Treatments

Novel role of thermomechanical grain boundary engineering in the microstructure evolution of austenitic stainless steel

The effect of special grain boundary development via the grain boundary engineering process (GBE) was explored in a bimodal microstructured 316L austenitic stainless steel with an average grain size of 1.92 μm. The GBE process was carried out by the rolling-annealing method via two routes of low and medium applied strain, followed by a short annealing period in a single-step and iterative manner. The grain boundary character distribution was obtained by Electron Backscatter Diffraction (EBSD) analysis, and the intergranular corrosion resistance and the tensile behavior of the samples were examined. Microstructural characterization showed that applying low strain repetitively increased the coincidence site lattice (CSL) and Σ3 boundaries percentage and created large twin-related domains (TRD). The reduced sensitization was attributed to a high proportion of CSLs and large-sized TRDs by applying a low-strain route. In the early stages of the low-strain route, the grain boundary character distribution showed a high number of primary twin nuclei in coarse grains and a continuous network of single twin nuclei in smaller grains, creating a high percentage of Σ3-grain boundaries. The low applied strain and the absence of the necessary driving force for the recrystallization and GBs migration led to the formation of twin nuclei, which would assist with the reduction of microstructure energy. A high percentage of Σ3 boundaries and an increase in the percentage of triple points consisting of low energy boundaries were found to be influential factors in increasing elongation.

Influence of aging treatment on corrosion behavior of extruded 2195 Al−Li alloy

The 2195 Al-Li alloy was processed by under-aging (UA), peak-aging (PA), double-aging (DA) and retrogression re-aging (RRA) treatments, and the microstructure, intergranular corrosion (IGC), exfoliation corrosion (EXCO) and stress corrosion cracking (SCC) behaviors were observed and discussed. The results show that the sequence of IGC and EXCO resistance is: RRA > UA > DA > PA. The low corrosion resistance of PA and UA is mainly caused by the continuous precipitation of T1 phases at grain boundaries to form continuous corrosion channels, while the interruption of corrosion channels caused by coarse and discontinuous T1 phases and wider precipitate free zone is the reason for the best corrosion resistance of RRA. The RRA alloy exhibits the best SCC resistance, and the order of SCC resistance is: RRA > DA > UA > PA. The discontinuous precipitation of intergranular T1 phases promotes the propagation of corrosion cracks across grain boundaries, thereby improving the SCC resistance.

Effect of ultrasonic vibration-assisted laser cladding frequency on the microstructure and properties of Fe-0.5C-15Cr alloy cladding layers

In this paper, Fe-0.5C-15Cr wear and corrosion resistant alloy coating was prepared on 3Cr13 stainless steel surface by ultrasonic vibration assisted laser cladding technology. The effects of ultrasonic vibration frequency on the microstructure, microhardness and corrosion resistance of the coating were studied. The results show that the length of the dendrites of the cladding layer decreased significantly after ultrasonic vibration is applied, the grains size is refined significantly, and the morphology of the grain boundary carbides changed from fishbone-like to short rods, when the vibration frequency is 20.2 kHz, the grain refinement is the most significant, and the orientation of the dendrites is obviously weakened. The hardness of the applied ultrasonic vibration specimens increased by 10–20 HV0.2 relative to the non-ultrasonic specimens, with the increase of vibration frequency, the hardness of the cladding layer firstly increased and then slightly decreased, and the peak appeared at 20.2 kHz. The coefficient of friction of the specimens when the ultrasonic frequency of 20.2 kHz is applied is lower than that of the specimens with non-ultrasonic frequency by 12.8 %, and the abrasive wear rate is reduced by 14.3 %. After ultrasonic vibration, the pitting potential of the cladding layer increases, the dimensional passivation current density decreased, the width of the passivation zone becomes wider, and the intergranular corrosion reactivation rate decreased, When the ultrasonic frequency is 20.2 kHz and 20.4 kHz, the pitting corrosion resistance and intergranular corrosion resistance of the cladding layer are significantly improved. This is because the cavitation effect, resonance effect and acoustic flow effect of ultrasonic vibration promote the non-uniform nucleation, refine the dendrites and intergranular carbides, and promote the redistribution of the corrosion-resistant element Cr in the in-grain martensite and grain boundary carbides, increasing the content of Cr in the matrix, and thus improving the wear resistance and corrosion resistance of the cladding layer.

Review on the application of stainless-clad bimetallic steel in the marine environment

PurposeStainless-clad bimetallic steels (SCBS) are widely investigated in some extremely environmental applications areas, such as polar sailing area and tropical oil and gas platforms areas, because of their excellent anticorrosion performance and relatively lower production costs. However, the properties of SCBS, including the mechanical strength, weldability and the anticorrosion behavior, have a direct relation with the manufacturing process and can affect their practical applications. This paper aims to review the application and the properties requirements of SCBS in marine environments to promote the application of this new material in more fields.Design/methodology/approachIn this paper, the manufacturing process, welding and corrosion-resistant properties of SCBS were introduced systematically by reviewing the related literatures, and some results of the authors’ research group were also introduced briefly.FindingsDifferent preparation methods, such as rolling composite, casting rolling composite, explosive composite, laser cladding and plasma arc cladding, as well as the process parameters, including the vacuum degree, rolling temperature, rolling reduction ratio, volume ratios of liquid to solid, explosive ratio and the heat treatment, influenced a lot on the properties of the SCBS through changing the interface microstructures. Otherwise, the variations in rolling temperature, pass, reduction and the grain size of clad steel also brought the dissimilarities of the mechanical properties, microhardness, bonding strength and toughness. Another two new processes, clad teeming method and interlayer explosive welding, deserve more attention because of their excellent microstructure control ability. The superior corrosion resistance of SCBS can alleviate the corrosion problem in the marine environment and prolong the service life of the equipment, but the phenomenon of galvanic corrosion should be noted as much as possible. The high dilution rate, welding process specifications and heat treatment can weaken the intergranular corrosion resistance in the weld area.Originality/valueThis paper summarizes the application of SCBS in marine environments and provides an overview and reference for the research of stainless-clad bimetallic steel.

Optimization of the Mechanical and Corrosion Resistance of Alloy 625 through Aging Treatments

In the as-annealed condition, the nickel-based Alloy 625 has excellent mechanical and corrosion properties compared to those of common stainless steels. This peculiarity enables its exploitation in several industrial fields at cryogenic and high temperatures and in the presence of severely corrosive atmospheres. However, in this alloy, when high-temperature plastic deformation processes and heat treatments are not carefully optimized, the occurrence of excessive grain coarsening can irremediably deteriorate the mechanical strength, possibly leading to incompatibility with the standard requirements. Therefore, this research work investigated the possibility of adopting single- and double-aging treatments aimed at improving such strength loss. Their optimization involved identifying the best compromise between the hardening effect and the loss in corrosion resistance induced by the simultaneous formation of intergranular chromium-rich carbides during aging. The investigation of the aging treatments was performed using hardness, tensile and intergranular corrosion tests considering different time–temperature combinations in a range from 621 °C to 732 °C. Double aging resulted in a considerable acceleration in the hardening response compared to single aging. However, even after its optimization in terms of both temperature and time, the intergranular corrosion resistance remained a critical aspect. Among all the tested conditions, only single aging at 621 °C for 72 h was acceptable in terms of both mechanical and corrosion properties. The influence of longer exposures will be investigated in a future study.

Triple structuration and enhanced corrosion performance of 316L in laser powder bed fusion

This work focuses on the influence of the feedstock powders on the microstructural properties and corrosion behavior of 316 L stainless steel (SS) produced by laser powder bed fusion (L-PBF) from two different suppliers. Microstructural investigations conducted after additive manufacturing reveal many particularities depending on the powders. These microstructural differences lead to a different corrosion behavior in boiling nitric acid containing oxidizing ions. The presence of the triple structuration (grains, large cells, small internal cells) shows a positive effect on intergranular and cellular corrosion resistance. In both cases, L-PBF 316 L SS provides better resistance to intergranular corrosion than wrought 316L SS.

Enhanced corrosion performance by controlling grain boundary precipitates in a novel crossover Al-Cu-Zn-Mg alloy by optimizing Zn content

The effect of Zn contents on grain boundary precipitates (GBPs), intergranular corrosion (IGC), and stress corrosion cracking (SCC) of crossover Al–Cu–Zn–Mg alloys was investigated. The increase in Zn contents accelerates the age-hardening response, and both matrix precipitates (MPs) and GBPs are transformed from S phase to S and η phases, while the width of the precipitates free zones (PFZs) first increases and then decreases. The narrowed PFZ width, coarse and discontinuous GBPs were able to inhibit anodic dissolution resulting in enhanced IGC resistance. The η phase inhibits anodic dissolution leading to an enhanced IGC resistance. First-principles calculations demonstrate that the GBPs surface with Mg termination planes shows a lower work function than that of Al leading to preferential anodic dissolution. The evolution of GBPs and PFZ widths changes the mechanism of SCC susceptibility for different Zn contents alloys from anodic dissolution and hydrogen embrittlement to anodic dissolution.

The Effect of Cu and Zn Addition on the Intergranular Corrosion Resistance of Al-Mg-Si Alloy

Aluminum alloys are widely used for automobile and aircraft industries because of their good strength-to-weight ratio. In general, Cu improves the strength of Al alloys but reduces localized corrosion resistance. For Al-Mg-Si alloys, it has been reported that Cu decreases intergranular corrosion resistance. In this study, the effect of Cu and Zn on intergranular corrosion resistance was analyzed by electrochemical measurements.As specimens, Cu-free alloy, Cu-added alloy, and Cu- and Zn-added alloy were prepared based on AA6061 composition. The extruded specimens were subjected to T6 heat treatment. Intermetallic compounds were characterized by SEM-EDS and TEM. Open-circuit potentials (OCPs) was measured in 0.1 M NaCl (pH 6.0). To assess the distribution density of the initiation sites of localized corrosion, the size of electrode area was 100 mm2, 9 mm2, or 1 mm2. In the electrochemical measurements, Ag/AgCl (3.33 M KCl) was used as the reference electrode.At the beginning of immersion, OCP was −1.2 V (vs. SHE) for all specimens, and OCP increased with time. After 4000 s, the OCP of Cu-free alloy became −0.5 V, the OCPs of Cu-added alloy and Cu- and Zn-added alloy became −0.4 V. After 3 h immersion, intergranular corrosion was generated on Cu-added alloy and Cu- and Zn-added alloy. In contrast, no intergranular corrosion was observed on Cu-free alloy. Based on intergranular corrosion length, it was shown that intergranular corrosion resistance of Cu- and Zn-added alloy is low compared with the others. This result suggested that Zn promotes the growth of intergranular corrosion. Moreover, the number of intergranular corrosion damages was assessed and found to be less on Cu- and Zn-added alloy than on Cu-added alloy. This result suggested that Zn decrease the number of initiation sites of intergranular corrosion. Additionally, 3-h immersion of Cu-added alloy and Cu- and Zn-added alloy was conducted with the electrode area of 9 mm2 and 1 mm2. For both alloys, intergranular corrosion occurred at 10 sites in 100 mm2 and 1 site in 9 mm2. And no intergranular corrosion occurred in the case of 1 mm2 electrode area. The distribution density of the initiation sites for intergranular corrosion on Cu-added alloy and Cu- and Zn-added alloy was estimated to be approximately 1 site per 9 mm2.

Improvement of intergranular corrosion resistance of SS 304L by grain refinement followed by gamma-ray irradiation treatment for the application in the back end of the nuclear fuel cycle

The severe plastic deformation (SPD) technique has been widely used for grain refinement to produce bulk ultra fine-grained (UFG) microstructure. In this study, an improved corrosion-resistant material of type 304L stainless steel (SS) has been designed, from the coarse-grain (CG) microstructure to the UFG microstructure using the SPD technique through cryo-rolling at liquid nitrogen (at 77K) temperature followed by gamma-ray irradiation treatment. In comparison to the effect of gamma-ray on both CG and UFG microstructure, both specimens were irradiated with an equal amount of doses. Gamma (γ) ray irradiation (dose rate: 2.83 kGy/h) affected the corrosion resistance of AISI type 304L stainless steel (in both CG and UFG) in concentrated nitric acid (65 wt%) medium. The correlation of irradiation effects on the microstructure and nitric acid corrosion behaviors has been discussed, which is important for designing materials for application in nuclear-spent fuel reprocessing plants.

Investigation of microstructure and corrosion resistance of an Al-Zn-Mg-Cu alloy under various ageing conditions

In this study, transmission electron microscopy and 3D optical profilometer were employed to investigate the effects of single-stage ageing and regression re-ageing treatments on the microstructure and corrosion resistance of Al-Zn-Mg-Cu alloy. The results indicate the intergranular corrosion resistance is increased by 36% with the regression re-ageing. Based on the semi-elliptical damage model, a 3D expansion model for pits is established. Meanwhile forms a systematic study of the formation mechanism, nucleation and growth of corrosion pits. This will contribute to the systematic and in-depth study of the corrosion resistance of Al-Zn-Mg-Cu alloy in aviation applications.

Investigation of Evolution of Microstructure, Mechanical Properties, and Corrosion Resistance of Novel Al-Mg-Si-Ag Alloy

In this paper, the evolution of the microstructure, mechanical properties, and intergranular corrosion (IGC) resistance of an Al-Mg-Si-Ag alloy is systematically investigated. For the as-cast alloy, the microstructure consists of the Mg2Si phase and Mg32(Al, Ag)49 phase. In the isothermal aging process, the novel alloy presents a significant age hardening effect. The ultimate tensile strength (UTS) and yield strength (YS) of the peak-aged alloy are 342 MPa and 231 MPa, respectively, which are 53 MPa and 84 MPa higher than that of the as-quenched alloy. The main strengthening phase at the peak-aged stage of the alloy is the MgAg phase, which has a body-centered cubic structure with a lattice constant of a = 0.33 nm. In addition, the IGC resistance of the peak-aged alloy is worse than that of other aged alloys. The corresponding microstructure of GBPs of the peak-aged alloy is more consecutive, and this is the main reason for the deterioration of IGC resistance of the alloy.

Improved heat and corrosion resistance of high electrical conductivity Al-Mg-Si alloys by multi-alloying of Ce, Sc and Y

In order to improve the corrosion and heat resistance of Al-Mg-Si alloy conductor materials, Ce, Sc, Y and Zr were added in Al-Mg-Si alloy to regulate the microstructure. The Al-Mg-Si-Ce-Sc-Y alloy was designed with excellent pitting and intergranular corrosion resistance by obtaining the micron-sized Fe-containing second phase with a lower potential difference to Al matrix, more dispersed grain boundary precipitates with a higher proportion of Si particles, narrower width of PFZ and ideal distribution of intergranular precipitates. The Al-Mg-Si-Ce-Sc-Y alloy also maintained higher hardness, strength and electrical conductivity after overaging and annealing and the corrosion/heat resistance mechanisms were proposed.

Effect of heat input on intergranular corrosion resistance and dry sliding wear of GTA welding of Hastelloy-X superalloy

Effect of heat input on intergranular corrosion resistance and dry sliding wear of GTA welding of Hastelloy-X superalloy