Showing papers on "Stress corrosion cracking published in 2022"

Effect of stress-aging treatment on the mechanical and corrosion properties of Al−Zn−Mg−Cu alloy

Abstract: A stress-aging treatment (SAT) was applied to an Al−Zn−Mg−Cu alloy to obtain a good combination of strength and corrosion resistance. The effect of SAT on stress corrosion cracking (SCC), electrochemical corrosion, microstructure, and mechanical properties of Al−Zn−Mg−Cu alloy was investigated systematically using scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD), transmission electron microscopy (TEM), slow strain rate tensile (SSRT), potentiodynamic polarization, etc. It was found that the number of matrix precipitates (MPs) under SAT increased and the size was reduced compared with that under stress-free aging treatment (SFAT). The MPs nucleated in large numbers due to the proliferation of dislocations caused by stress, and the alloy under SAT had a higher strength and earlier peak aging time than SFAT. In addition, large-sized and discontinuous grain boundary precipitates (GBPs) hindered the anodic dissolution of the grain boundaries (GBs) and the propagation of SCC, which improved the corrosion resistance of the alloy. This study has important guiding significance for rationally formulating the SAT process of Al−Zn−Mg−Cu alloys and improving alloy corrosion performance.

Real-time strain monitoring of reinforced concrete under the attacks of sulphate and chloride ions based on XCT and DIC methods

Abstract: In this work, the influences of different sulphate and chloride laden environment on the corrosion of reinforced concrete have been examined in real time by the digital image correlation (DIC) technology combined with a traditional strain measurement, and the applicability of DIC technology for monitoring the entire life cycle of reinforced concrete is verified. The main testing parameters include: (1) electrical current between steel bar and stainless steel sheet are measured by ampere meter, (2) expansion strain values are obtained by the traditional strain measurement, (3) micro-strain fields are obtained by the DIC technology. According to the above parameters, the influence of chloride and sulphate ions on the corrosion process of concrete reinforcement can be compared and analysed. The obtained results reveal that sulphate ions inhibit the corrosion of steel bars and suppress the corrosion effect produced by chloride ions. In addition, a model for predicting the corrosion-induced expansion stress at the steel–concrete interface is established, and its time variation is accurately quantified. The critical corrosion-induced expansion stress generated in reinforced concrete under the action of a single chloride salt solution is 2.25 MPa, and the corresponding initial cracking time is equal to 100 h. Meanwhile, the corrosion-induced expansion stress of the reinforced concrete specimen exposed to a composite solution of chloride and sulphate ions is 2.0 MPa, and its initial cracking time equals 150 h.

Real-time strain monitoring of reinforced concrete under the attacks of sulphate and chloride ions based on XCT and DIC methods

Abstract: In this work, the influences of different sulphate and chloride laden environment on the corrosion of reinforced concrete have been examined in real time by the digital image correlation (DIC) technology combined with a traditional strain measurement, and the applicability of DIC technology for monitoring the entire life cycle of reinforced concrete is verified. The main testing parameters include: (1) electrical current between steel bar and stainless steel sheet are measured by ampere meter, (2) expansion strain values are obtained by the traditional strain measurement, (3) micro-strain fields are obtained by the DIC technology. According to the above parameters, the influence of chloride and sulphate ions on the corrosion process of concrete reinforcement can be compared and analysed. The obtained results reveal that sulphate ions inhibit the corrosion of steel bars and suppress the corrosion effect produced by chloride ions. In addition, a model for predicting the corrosion-induced expansion stress at the steel–concrete interface is established, and its time variation is accurately quantified. The critical corrosion-induced expansion stress generated in reinforced concrete under the action of a single chloride salt solution is 2.25 MPa, and the corresponding initial cracking time is equal to 100 h. Meanwhile, the corrosion-induced expansion stress of the reinforced concrete specimen exposed to a composite solution of chloride and sulphate ions is 2.0 MPa, and its initial cracking time equals 150 h.

Surface characteristics and stress corrosion behavior of AA 7075-T6 aluminum alloys after different shot peening processes

Abstract: Shot peening is often reported as being beneficial to stress corrosion cracking resistance; however, the increased surface roughness induced by shot peening may promote localized corrosion pitting. Here, AA 7075-T6 aluminum alloys were treated by different shot peening processes, and the surface characteristic, including refined microstructure, residual stress and surface roughness, were characterized, then its effect on localized corrosion pitting and stress crack propagation behavior were investigated. Compared with single shot peening, the microstructure refinement was not further enhanced by dual shot peening with adding a subsequent low intensity of micro-shot peening. The surface residual stress distribution become more uniform, and the average surface residual stress value was increased from −158 MPa to −175 MPa. The maximum residual stress was synchronously increased from −302 MPa to −319 MPa. Meanwhile, the surface roughness (Ra) value was decreased from 4.05 μm to 2.05 μm. Compared with single shot peening, the degree of surface localized corrosion pitting was alleviated after dual shot peening due to its low surface roughness and more uniform compressive residual stress distribution. The depth of stress corrosion cracking for dual shot peening was decreased with a minimum value of 33 μm, which may be ascribed to the high maximum compressive residual stress at the subsurface.

Study of pre-strain before artificial aging on mechanical property and stress corrosion behavior of 2297 Al–Cu–Li alloy

Abstract: The influence of pre-strain (2%, 5%, 8% and 12.5%) and aging state (under, peak and over aging) on mechanical properties and stress corrosion behavior of 2297 Al–Cu–Li alloy was studied. The peak microhardness of the alloy reaches 156.3 HV at 15 h with 12.5% pre-strain, and that of the alloy is only 115.6 HV at 31 h without pre-strain. The slow strain rate testing results indicate the low stress corrosion cracking factor for the samples without pre-strain and high stress corrosion cracking factor for the samples with pre-strain, and the stress corrosion cracking factor of the peak-aged sample with 12.5% pre-strain reaches to 33.3%. From the transmission electron microscopy characterization, it can be inferred that the quantity and distribution of T1 (Al2CuLi) precipitates significantly affect the stress corrosion behavior of 2297 Al–Cu–Li alloy. The over-aged sample exhibits poor stress corrosion resistance, resulting from the large numbers of coarse T1 precipitates and precipitation free zone at the grain boundary.

Influence of Microstructure on Stress Corrosion Cracking of X100 Pipeline Steel in Carbonate/Bicarbonate Solution

Abstract: The stress corrosion cracking (SCC) behaviors of X100 pipeline steels with different heat-treated microstructures in carbonate/bicarbonate solution at various potentials were investigated in this study. Several analyses were performed using electrochemical measurements, slow strain rate tensile (SSRT) tests, scanning electron microscopy (SEM), and electron back-scattered diffraction (EBSD). The results showed that the SCC susceptibilities of heat-treated microstructures increase as the cathodic potential shifts from −850 to −1200 mVvsSCE. At a weak cathodic potential, the different microstructures show clear SCC sensitivity, showing that hydrogen cannot be ignored in this circumstance when the alkaline environment is not considered seriously. At a mild cathodic potential, hydrogen sensitivity controls SCC behavior, but at a larger negative potential, both electrochemical effect and hydrogen sensitivity influence SCC behavior. The SCC cracks propagate along the high angle grain boundary (HAGB) at open circuit potential (OCP) and as the applied potential is adjusted negatively, the cracks would either follow low angle grain boundary (LAGB), HAGB or random orientation propagation paths. The synergistic influence of dislocation, grain boundary, grain size, martensite/austenite (M/A) island, and carbide controls the SCC process of the X100 pipeline. SCC susceptibility was shown to be high in microstructures with coarse grain and high dislocation density, whereas grain boundaries such as the martensite/austenite (M/A) island and carbide offer sites for SCC initiation.

On the corrosion, stress corrosion and cytocompatibility performances of ALD TiO2 and ZrO2 coated magnesium alloys.

Abstract: Magnesium alloys are increasingly studied as materials for temporary implants. However, their high corrosion rate and susceptibility to corrosion-assisted cracking phenomena, such as stress corrosion cracking (SCC), continue to prevent their mainstream use. Recently, coatings have been considered to provide an effective solution to these issues and researchers have focused their attention on Atomic Layer Deposition (ALD). ALD stands out as a coating technology due to the outstanding film conformality and density achievable, and has shown encouraging preliminary results in terms of reduced corrosion rate and reduced SCC susceptibility. Here, we contribute to the ongoing interest in ALD-coated Mg alloys, providing a comprehensive characterisation of the effect of 100 nm thick ALD TiO2 and ZrO2 coatings on the corrosion behaviour and SCC susceptibility of AZ31 alloy. Moreover, we also investigate the effect of these coatings on the induced biological response. Our results suggest that the ALD coatings can improve the corrosion and SCC resistance of the Mg alloy, with the ZrO2 ALD coating showing the best improvements. We suggest that the different corrosion behaviours are the cause of the cytocompatibility results (only the ZrO2 ALD coating was found to meet the demands for cellular applications). Finally, we leverage on considerations about the coatings’ wettability, electrochemical stability and surface integrity to justify the different results.

Revisiting stress-corrosion cracking and hydrogen embrittlement in 7xxx-Al alloys at the near-atomic-scale

Abstract: Abstract The high-strength 7xxx series aluminium alloys can fulfil the need for light, high strength materials necessary to reduce carbon-emissions, and are extensively used in aerospace for weight reduction purposes. However, as all major high-strength materials, these alloys can be sensitive to stress-corrosion cracking (SCC) through anodic dissolution and hydrogen embrittlement (HE). Here, we study at the near-atomic-scale the intra- and inter-granular microstructure ahead and in the wake of a propagating SCC crack. Moving away from model alloys and non-industry standard tests, we perform a double cantilever beam (DCB) crack growth test on an engineering 7xxx Al-alloy. H is found segregated to planar arrays of dislocations and to grain boundaries that we can associate to the combined effects of hydrogen-enhanced localised plasticity (HELP) and hydrogen-enhanced decohesion (HEDE) mechanisms. We report on a Mg-rich amorphous hydroxide on the corroded crack surface and evidence of Mg-related diffusional processes leading to dissolution of the strengthening η-phase precipitates ahead of the crack.

Study of pre-strain before artificial aging on mechanical property and stress corrosion behavior of 2297 Al–Cu–Li alloy

Abstract: The influence of pre-strain (2%, 5%, 8% and 12.5%) and aging state (under, peak and over aging) on mechanical properties and stress corrosion behavior of 2297 Al–Cu–Li alloy was studied. The peak microhardness of the alloy reaches 156.3 HV at 15 h with 12.5% pre-strain, and that of the alloy is only 115.6 HV at 31 h without pre-strain. The slow strain rate testing results indicate the low stress corrosion cracking factor for the samples without pre-strain and high stress corrosion cracking factor for the samples with pre-strain, and the stress corrosion cracking factor of the peak-aged sample with 12.5% pre-strain reaches to 33.3%. From the transmission electron microscopy characterization, it can be inferred that the quantity and distribution of T 1 (Al 2 CuLi) precipitates significantly affect the stress corrosion behavior of 2297 Al–Cu–Li alloy. The over-aged sample exhibits poor stress corrosion resistance, resulting from the large numbers of coarse T 1 precipitates and precipitation free zone at the grain boundary.

Effect of ultrasonic impact treatment on microstructure and corrosion behavior of friction stir welding joints of 2219 aluminum alloy

Abstract: Ultrasonic Impact Treatment (UIT) was performed to improve the corrosion resistance of 2219 aluminum alloy friction stir welding (FSW) joints. Results showed that the coarse grains on near surface of FSW joints were obviously modified and refined after UIT, and the thickness of the modified layer of different sub-regions was ranged from 90 to 120 μm. UIT increased intergranular corrosion resistance of 2219 aluminum alloy FSW joints in salt spray corrosion atmosphere. Free-corrosion potential of heat-affected zone (HAZ), which presented the worst corrosion resistance, was increased from −0.653 to −0.628 V, and the corrosion current density was decreased from 7.48 to 6.18 mA cm −2 . The sensitivity index of stress corrosion cracking (SCC) of the joints was decreased from 0.139 to 0.129 in 3.5% NaCl solution after UIT, and the risk of crack initiation during SCC process was significantly inhibited. UIT improved the SCC resistance of 2219 aluminum alloy FSW joints by surface plasticity improvement, grain refinement and precipitates dissolution and redistribution.

A generalised, multi-phase-field theory for dissolution-driven stress corrosion cracking and hydrogen embrittlement

Abstract: We present a phase field-based electro-chemo-mechanical formulation for modelling mechanics-enhanced corrosion and hydrogen-assisted cracking in elastic–plastic solids. A multi-phase-field approach is used to present, for the first time, a general framework for stress corrosion cracking, incorporating both anodic dissolution and hydrogen embrittlement mechanisms. We numerically implement our theory using the finite element method and defining as primary fields the displacement components, the phase field corrosion order parameter, the metal ion concentration, the phase field fracture order parameter and the hydrogen concentration. Representative case studies are addressed to showcase the predictive capabilities of the model in various materials and environments, attaining a promising agreement with benchmark tests and experimental observations. We show that the generalised formulation presented can capture, as a function of the environment, the interplay between anodic dissolution- and hydrogen-driven failure mechanisms; including the transition from one to the other, their synergistic action and their individual occurrence. Such a generalised framework can bring new insight into environment–material interactions and the understanding of stress corrosion cracking, as demonstrated here by providing the first simulation results for Gruhl’s seminal experiments.