Stress Corrosion Cracking Susceptibility Research Articles

Inhomogeneity and anisotropy of Al-Zn-Mg-Cu alloy manufactured by wire arc additive manufacturing: microstructure, mechanical properties, stress corrosion cracking susceptibility

ABSTRACT In this study, Al-Zn-Mg-Cu alloy components were prepared using wire arc additive manufacturing (WAAM). Through multi-scale characterisation technology, performance testing and slow strain rate tensile (SSRT) testing, the microstructure, mechanical properties and stress corrosion cracking (SCC) susceptibility of WAAM Al-Zn-Mg-Cu components were studied, revealing the generation mechanism of inhomogeneity and anisotropy. The results show that with the increase of WAAM thermal cycles, the matrix precipitates (MPs), grain boundary precipitates (GBPs) and precipitation-free zones (PFZ) evolve in different paths and increase to varying degrees, resulting in performance decrease and increase in stress corrosion susceptibility, so the inhomogeneity is mainly attributed to differences in precipitated phases. The Inter-layer inclined to the scanning direction and the Inner-layer inclined to the building direction led to anisotropy in tensile strength and SCC behaviour, so the anisotropy is mainly attributed to the grain orientation and fracture mode.

Effects of surface finishes, heat treatments and printing orientations on stress corrosion cracking behavior of laser powder bed fusion 316L stainless steel in high-temperature water

Stress corrosion cracking (SCC) of laser powder bed fusion 316 L stainless steel in oxygenated high-temperature water environments with chloride addition at 288 °C was studied. The influences of surface finishes (as-built, mechanically polished, Hirtisation® and shot peened), heat treatments (solution annealing at 1066 and 1150 °C and hot isostatic pressing) and the printing orientations on SCC were evaluated. Hirtisation resulted in a lower SCC susceptibility than as-built or polished surface while shot peening showed the lowest apparent SCC resistance. A high annealing temperature decreases SCC resistance. The effect of printing orientation is material and environment dependent.

Influence of cathodic polarization on stress corrosion cracking susceptibility of 35CrMo steel for high strength bolt in simulated deep-sea environment

The effect of cathodic polarization on stress corrosion cracking (SCC) of 35CrMo steel for high strength bolt in the simulated deep-sea environment has been studied. The results show that 35CrMo steel has a higher SCC sensitivity at open circuit potential in the simulated deep-sea environment than that in the shallow seawater. With potential negatively shifted to −750 mV, 35CrMo steel presents the lowest SCC sensitivity. And the SCC susceptibility is increased significantly with the further negative shift of potential because of the intensive hydrogen evolution. When the potential is below −950 mV, hydrogen embrittlement with hydrogen-enhanced-plasticity mediated decohesion should be the dominant SCC micro-mechanism.

Effect of laser shock peening on stress corrosion cracking of TC4/2A14 dissimilar metal friction stir welding joints

Stress corrosion cracking (SCC) of welded joints is a significant issue that affects the widespread application of multimetal welded structures in aerospace, transportation, and other fields. This paper investigates the effect of laser shock peening (LSP) on the SCC of TC4/2A14 friction stir welded (FSW) joints with dissimilar metals. The microstructural evolution, mechanical properties, and corrosion behavior with and without LSP treatment were investigated using optical microscopy, transmission electron microscopy, X-ray analysis, electrochemical testing, and slow strain rate tensile testing (SSRT). The results showed that the LSP significantly refined the grains and induced work-hardening on the near-surface of the material. After LSP, the compressive residual stresses on the surface of the titanium and aluminium sides were −817.6 MPa and −153.6 MPa for the joint, respectively. Corrosion resistance was also improved, with the self-corrosion current density on the Al side of the joints reduced by 77% and the SCC susceptibility index (Issrt) reduced from 0.140 to 0.121. The enhanced SCC resistance of the LSP-treated TC4/2A14 dissimilar metal FSW joints is primarily due to grain refinement, work-hardening effect, and high-level compressive residual stress. These factors not only enhance the material strength and improve the pitting resistance of the joints but also prevent the initiation and propagation of SCC.

Data analysis of the influence of microstructure, composition, and loading conditions on stress corrosion cracking behavior of Mg alloys

Stress corrosion cracking (SCC) can be a crucial problem in applying rare earth (RE) Magnesium alloys in environments where mechanical loads and electrochemical driven degradation processes interact. It has been proven already that the SCC behavior is associated with microstructural features, compositions, loading conditions, and corrosive media, especially in-vivo. However, it is still unclear when and how mechanisms acting on multiple scales and respective system descriptors predictable contribute to SCC for the wide set of existing Mg alloys. In the present work, suitable literature data along SCC of Mg alloys has been analyzed to enable the development of a reliable SCC model for MgGd binary alloys. Pearson correlation coefficient and linear fitting are utilized to describe the contribution of selected parameters to corrosion and mechanical properties. Based on our data analysis, a parameter ranking is obtained, providing information on the SCC impact with regard to ultimate tensile strength (UTS) and fracture elongation of respective materials. According to the analyzed data, SCC susceptibility can be grouped and mapped onto Ashby type diagrams for UTS and elongation of respective base materials tested in air and in corrosive media. The analysis reveals the effect of secondary phase content as a crucial materials descriptor for our analyzed materials and enables better understanding towards SCC model development for Mg-5Gd alloy based implant.

Stress corrosion cracking behavior and mechanism of 2205 duplex stainless steel under applied polarization potentials

In this work, a non-steady electrochemical model for assessing stress corrosion cracking (SCC) of 2205 duplex stainless steel (DSS) under applied polarization potentials was proposed, and the SCC mechanism was revealed. With the negative shift of potentials, hydrogen enhances SCC susceptibility by deteriorating passive film, inhibiting repassivation and causing serious damage. In particular, at −850 mV (vs. SCE), the synergetic effect of anodic dissolution (AD) and hydrogen embrittlement (HE) causes severe pitting and SCC. The negative shift of applied potentials changes the preferential pit/SCC initiation site due to high hydrogen concentration in austenite.

Investigating the Impact of Physical Vapour Deposition (PVD)-Coated Cutting Tools on Stress Corrosion Cracking Susceptibility in Turning Super Duplex Stainless Steel

This work aimed to ascertain the corresponding influences of several PVD-coated cutting tools on the susceptibility of the machined surface of super duplex stainless steel (SDSS) to stress corrosion cracking. Coatings comprised of AlCrN, AlCrN/TiSiN, and AlTiN were applied to cemented carbide cutting tools using the PVD method; these were then used to turn the outer surface of the SDSS tube section. During the cutting process, the material presents the following combination of features: (i) a tendency for strain hardening, reflected in microstructural modifications and residual stresses of the machined surface and (ii) high temperatures in the cutting region, reducing the tool life. The goal of this work was to evaluate the surface integrity (work hardening and corrosion behaviour) of the SDSS obtained after the machining process (finish turning) with cemented carbide tools coated with three different PVD coatings.

Effect of strain rate on the stress corrosion cracking of TP439 stainless steel in water vapor environment at 500 ℃

The effect of water vapor on the stress corrosion cracking (SCC) behavior of TP439 stainless steel at 500 °C was investigated using slow strain rate tensile tests at three strain rates of 2 × 10–5/s, 2 × 10–6/s, and 2 × 10–7/s. Air was selected as a comparative blank test environment for the water vapor environment. The results showed that the tensile strength of the specimens increased significantly in air when the strain rate was decreased from 2 × 10–5/s to 2 × 10–7/s, while it decreased in water vapor. Dynamic strain aging (DSA) and SCC are the main factors contributing to the difference in tensile strength of the specimens in air and water vapor. The SCC of TP439 stainless steel in water vapor at 500 °C occurs at a strain rate of 2 × 10–7/s or even lower. Based on the SCC susceptibility index and SEM observation of specimen fracture, TP439 stainless steel exhibits a slight transgranular SCC in water vapor with low SCC susceptibility.

Mechanism and evaluation method of stress corrosion susceptibility of 904L stainless steel with optimized structure in seawater

The stress corrosion cracking (SCC) and the electrochemical behavior of 904 L stainless steel in a simulated seawater environment were investigated using slow strain rate testing (SSRT), electrochemical polarization, electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) curves. The sensitive potential range of 904 L stainless steel was determined by the fast and slow scan potential polarization curve, is − 950 mVSCE ∼ 270 mVSCE. Moreover, with the negative shift of applied potential, the toughness fracture characteristic of the three kinds of steel is reduced, and the sensitization state steel is the most obvious reduction. Finally, a practical formula for evaluating the SCC susceptibility of 904 L stainless steel was developed by integrating data from SSRT and fast and slow scan polarization curves.

In vitro evaluation of stress corrosion cracking susceptibility of PEO-coated rare-earth magnesium alloy WE43

Controlling material degradation in complex mechanobiological environments is the current challenge in advancing biodegradable magnesium implants for orthopaedic applications. Understanding stress corrosion cracking (SCC) mechanisms of magnesium alloy-coating systems in physiological fluids facilitates the design of magnesium implants with excellent biomedical performance. In this study, we investigated the SCC behaviour of a medical grade PEO-coated magnesium alloy WE43 under different loading conditions. Constant loadings tests (CLT) and slow strain rate tests (SSRT) were conducted to evaluate the SCC susceptibility of this alloy-coating system under in vitro conditions. Fracture surfaces of the non-coated and PEO-coated specimens were characterised by scanning electron microscopy to reveal the SCC mechanisms under different loading configurations. The experimental results showed that the alloy-coating system exhibits a high SCC resistance in SSRT conditions. However, high stress levels and plastic deformations lead to a significant acceleration of the SCC process. Moreover, the fracture surface analysis demonstrated that the brittle nature of the PEO coating deteriorates the mechanical integrity of the alloy under critical mechanical loadings, which results in an increased susceptibility towards stress corrosion cracking of the coated WE43.

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.

Influence of AC/DC on stress corrosion cracking of Ti-6Al-3Nb-2Zr-1Mo alloy in simulated marine solution

The study investigated the influence of alternating current (AC) and direct current (DC) on stress corrosion cracking (SCC) behavior of Ti-6Al-3Nb-2Zr-1Mo (Ti80) alloy in simulated marine solution with different pH levels. Electrochemical measurements, slow strain rate tensile (SSRT) tests and fracture morphology analysis were used to evaluate SCC behavior. Under conditions of pH = 2 or 1, AC enhances SCC susceptibility by disrupting the passive film, primarily attributed to anodic dissolution and hydrogen embrittlement. When both AC and DC coexist, the excessively negative potential intensifies the hydrogen evolution reaction, leading to hydrogen embrittlement dominating the SCC mechanism of Ti80.

Integrity Assessment of Stress Corrosion Cracking Susceptibility of Duplex UNS S32205 and Austenitic UNS S31653 Stainless Steel Reinforcements

Integrity Assessment of Stress Corrosion Cracking Susceptibility of Duplex UNS S32205 and Austenitic UNS S31653 Stainless Steel Reinforcements

Potentiostatic preparation and in vitro characterization of functional hazenite conversion coatings on AZ31 magnesium alloy

A functional hazenite coating was deposited on AZ31 Mg alloy by polarization at −0.8 V in a deaerated phosphate solution containing 0.1 M K2HPO4 and 0.1 M Na2HPO4 with pH 9. The growth process of the coating was determined by analyzing its morphological and composition evolution. The roughness, hydrophilicity, long-term protectiveness, bioactivity and bio-compatibility of the coating were characterized. The stress corrosion cracking (SCC) susceptibility of the coated AZ31 Mg alloy was also investigated. The results showed that the coating consisted of crystallized Mg(OH)2, MgHPO4·3H2O, KMgPO4·6H2O and KNaMg2(PO4)2·14H2O. The latter three compounds were transformed into hydroxyapatite, improving the bioactivity of AZ31 Mg alloy. The coating increased the roughness and hydrophilicity and significantly stimulated the proliferation of rabbit bone marrow stem cells, enhancing the biocompatibility of AZ31 Mg alloy. Additionally, the coating reduced the degradation rate of AZ31 Mg alloy by more than two orders of magnitude and the hydrogen volume by 50.9 % and showed good long-term protectiveness. Moreover, the coating decreased the SCC susceptibility indexes IUTS and Iε of AZ31 Mg alloy by 41.9 % and 44.9 %, respectively.

Understanding the non-steady electrochemical mechanism on SCC of 304 SS under applied polarization potentials

In this work, the non-steady electrochemical model on stress corrosion cracking (SCC) was established, which was verified by SCC of 304 SS with various microstructures. SCC mechanism depends on applied potentials including anodic dissolution (AD), hydrogen embrittlement (HE) and AD+HE, and the potential range for each mechanism was determined with the critical potentials on slow/fast scan potentiodynamic curves. The quantitative relationship of SCC susceptibility and applied potentials is acquired with the model, which is effective for assessing SCC. It was verified by 304 SS with various microstructures, which presents similar non-steady electrochemical characteristics and SCC susceptibility.

Effect of non-isothermal creep aging on the microstructure, mechanical properties and stress corrosion cracking resistance of 7075 alloy

The effect of non-isothermal creep aging (NICA) on the microstructure, mechanical properties, and stress corrosion cracking (SCC) resistance of 7075 alloy was investigated. The results showed that the tensile strength of the alloy increased to 565 MPa when the alloy was heated to 210 °C (CH210) and reached 580 MPa when it was subsequently cooled to 120 °C (CC120). Simultaneously, the SCC susceptibility of rtf increased from 50.8 % to 98.4 %. As compared with traditional creep aging process [1], a large strength increment with excellent stress corrosion resistance have been obtained by NICA. The microstructure revealed that a lot of dislocations have been introduced by creep during the heating stage which could improve the precipitates volume fraction and accelerate the diffusion of solutes; while during the cooling stage, η′ was greatly refined, and GPI and GPⅡ were re-precipitated from the matrix due to the decreased solid solubility and increased critical radius R*; both of them are responsible for the continuous strength increase during NICA. Moreover, the width of the precipitate free zone (PFZ) was narrowed from 46.1 nm (CH210) to 28.6 nm (CC120). The microchemical analysis reveals that solutes were more homogenously distributed in grain boundary precipitates (GB-ppts), matrix precipitates, the PFZ, and the matrix with the help of creep. The narrower PFZ and homogeneous solute distribution are responsible for improving the SCC susceptibility in the CC120 alloy.

Combining turning with slide burnishing to improve surface integrity and stress corrosion resistance

The surface characteristics play a pivotal role in stress corrosion cracking (SCC) resistance and fatigue life. Strengthening and modifying the material surface properties during manufacturing is a promising approach to improving the component service performance. Therefore, this study proposes a new surface finishing and strengthening mode that combines turning with slide burnishing (TSB) with a common turning tool. The core idea is that the cutting edge of the tool removes the material surface layer as a chip while the tool corner with a large radius performs a slide burnishing process on the manufactured surface. The machining-induced surface integrity in terms of residual stress, surface roughness, micro-hardness and microstructure changes was examined, and the SCC susceptibility was tested in a strong corrosion environment. The results showed that the surfaces processed by TSB suffered lower biaxial residual stresses, higher micro-hardness and deeper hardened layer when compared with the traditional turned surfaces. Besides, it was observed the TSB processed surfaces were less susceptible to SCC initiation which could be attributed to the lower residual stress introduced by TSB. Additionally, the multi-pass TSB treated surfaces showed significant low SCC susceptibility. Consequently, this work suggests that the surface integrity and the service performance like SCC resistance can be improved by TSB.

Enhanced hydrogen induced stress corrosion cracking resistance of Ni-advanced weathering steel by Ni and Mn modification

The stress corrosion cracking (SCC) behavior of three kinds of Ni-advanced weathering steel and a common weathering steel are examined in a simulated harsh marine environment by X-ray diffraction, scanning electron microscopy, electron backscattered diffraction, transmission electron microscopy, electrochemical tests, and slow strain rate tensile tests under different applied potentials. The results show that the SCC susceptibility of all test steel is low at open circuit potential. However, the SCC sensitivity of the conventional weathering steel increases significantly at − 1200 mV, while the Ni-advanced weathering steel exhibits good resistance to hydrogen embrittlement, which is attributed to the improved stacking fault energy, decrease of martensite-austenite constituents and refined grain size caused by increase in Ni and Mn content.

Evaluation of the impact of chloride ion concentration on stress corrosion cracking in E690 steel under low pH conditions

In this work, the effect of Cl- concentration on the stress corrosion cracking (SCC) behavior of E690 steel in low pH solution was studied. The SCC behavior of E690 steel is controlled by the combination of anodic dissolution and hydrogen embrittlement. The Cl- concentration has a significant effect on the electrochemical reaction, and icorr and Ecorr increase first and then decrease as the Cl- concentration increases from 0.5 to 4.0 mol/L. The SCC behavior of E690 steel is affected by the electrochemical reaction. Thus, the SCC susceptibility increases first and then decreases as the Cl- concentration increases from 0.5 to 4.0 mol/L.

Study on the wear resistance and corrosion behaviour of self-sealed MAO/ZrO2 coatings prepared on 7075 aluminium alloy

Self-sealed microarc oxidation (MAO) coatings were prepared on 7075 aluminium alloy by incorporating different concentrations of ZrO2 particles. The wear resistance and corrosion behaviour of MAO- and MAO/ZrO2-coated alloys were investigated. The results show that the tribological behaviour of the coatings was controlled by an abrasive mechanism. The coefficient of friction (COF) for the MAO/ZrO2-coated samples decreased to 0.82, indicating that the wear resistance was significantly improved due to the incorporation of hard ZrO2 particles and the enhanced compactness and surface roughness of the coatings. The sealed pores effectively prevented the permeation of the corrosion solution, thus increasing the electrochemical corrosion resistance. Pores and microcracks would be enlarged and preferentially fractured during slow strain rate testing (SSRT) and thus were the initial sites for corrosion pitting and SCC crack propagation. The interlocking mechanism between the pores (microcracks) and ZrO2 particles enhanced the strength of the pores (microcracks); therefore, the stress corrosion cracking (SCC) susceptibility of the MAO/ZrO2-coated samples was also reduced. Moreover, the MAO/ZrO2 coatings formed with the addition of 4 g/L ZrO2 particles had the best corrosion resistance, and the SCC susceptibility was reduced by 8.1% compared with that of the Al matrix.