Search

Effects of Mo and C addition on the microstructural evolution and corrosion resistance in chloride solution of FeNiCrAl duplex alloy were investigated. The results showed that α phase stabilizing element Mo increased the α/γ volume ratio and γ phase stabilizing element C decreased its ratio in FeNiCrAl alloy, and the chemical composition of α and γ phases was changed by Mo and C addition, which affected the corrosion resistance of FeNiCrAl alloy. Pitting corrosion mainly occurred in α phase around NbC precipitated at α/γ interface due to the micro-galvanic corrosion (MGC) effect between α (anode), γ (cathode) and NbC (cathode) phases. The pitting corrosion resistance was improved by Mo and C addition, resulting from that Mo and C enhanced the passivity of passive films and decreased the MGC effect between α, γ and NbC phases.

Revealing the localized corrosion process of Mg alloy is considered as one of the most significant ways for improving its corrosion resistance. The reliable monitor should be high distinguishability and real-time in liquid environment. Herein, Mg-9Al-1Fe and Mg-9Al-1Fe-1Gd alloys were designed to highlight the impact of intermetallic on the corrosion behaviour. In-situ AFM with a special electrolyte circulation system and quasi-in-situ SEM observation were used to monitor the corrosion process of the designed alloys. SEM-EDS and TEM-SAED were applied to identify the intermetallic in the designed alloys, and their volta potentials were measured by SKPFM. According to the real-time and real-space in-situ AFM monitor, the corrosion process consisted of dissolution of anodic α-Mg phase, accumulation of corrosion products around cathodic phase and shedding of some fine cathodic phase. Then, the localized corrosion process of Mg alloy was revealed combined with the results of the monitor of corrosion process and Volta potential difference.

Revealing the localized corrosion process of Mg alloy is considered as one of the most significant ways for improving its corrosion resistance. The reliable monitor should be high distinguishability and real-time in liquid environment. Herein, Mg-9Al-1Fe and Mg-9Al-1Fe-1Gd alloys were designed to highlight the impact of intermetallic on the corrosion behaviour. In-situ AFM with a special electrolyte circulation system and quasi-in-situ SEM observation were used to monitor the corrosion process of the designed alloys. SEM-EDS and TEM-SAED were applied to identify the intermetallic in the designed alloys, and their volta potentials were measured by SKPFM. According to the real-time and real-space in-situ AFM monitor, the corrosion process consisted of dissolution of anodic α-Mg phase, accumulation of corrosion products around cathodic phase and shedding of some fine cathodic phase. Then, the localized corrosion process of Mg alloy was revealed combined with the results of the monitor of corrosion process and Volta potential difference. [ABSTRACT FROM AUTHOR]

For the sake of improving the mechanical properties and corrosion resistance of biodegradable Mg alloy synergistically, various content of element V (0, 0.05, 0.10, 0.15, 0.20 wt.%) are introduced into an Mg-Zn-Y alloy with long-period stacking ordered (LPSO) structure, and the effects of V on its microstructure, mechanical properties and corrosion resistance are investigated systematically. The results indicate that the grains are effectively refined by V addition, and the primary α-Mg in Mg-Zn-Y-V0.1 alloy is most significantly refined, with grain size being decreased by 62%. The amount of 18R LPSO structure is increased owing to the V addition. The growth mode of the second phase (W-phase and 18R LPSO structure) is transformed to divorced growth pattern, which ascribes to the thermodynamic drive force of V to promote the nucleation of LPSO phase. Thus, 18R LPSO structure presents a continuous distribution. Due to grains refinement and modification of second phase, the tensile strength and strain of alloys are both enhanced effectively. Especially, the ultimate tensile strength and the elongation of V0.1 alloy are 254 MPa and 15.26%, which are 41% and 61% higher than those of V-free alloy, respectively. Owing to the continuously distributed 18R LPSO structure with refined grains and stable product film, the weight loss and hydrogen evolution corrosion rates of V0.1 alloy are 7.1 and 6.2 mmy−1, respectively, which are 42.6% and 45.4% lower than those of V-free alloy.

For the sake of improving the mechanical properties and corrosion resistance of biodegradable Mg alloy synergistically, various content of element V (0, 0.05, 0.10, 0.15, 0.20 wt.%) are introduced into an Mg-Zn-Y alloy with long-period stacking ordered (LPSO) structure, and the effects of V on its microstructure, mechanical properties and corrosion resistance are investigated systematically. The results indicate that the grains are effectively refined by V addition, and the primary α-Mg in Mg-Zn-Y-V0.1 alloy is most significantly refined, with grain size being decreased by 62%. The amount of 18R LPSO structure is increased owing to the V addition. The growth mode of the second phase (W-phase and 18R LPSO structure) is transformed to divorced growth pattern, which ascribes to the thermodynamic drive force of V to promote the nucleation of LPSO phase. Thus, 18R LPSO structure presents a continuous distribution. Due to grains refinement and modification of second phase, the tensile strength and strain of alloys are both enhanced effectively. Especially, the ultimate tensile strength and the elongation of V0.1 alloy are 254 MPa and 15.26%, which are 41% and 61% higher than those of V-free alloy, respectively. Owing to the continuously distributed 18R LPSO structure with refined grains and stable product film, the weight loss and hydrogen evolution corrosion rates of V0.1 alloy are 7.1 and 6.2 mmy−1, respectively, which are 42.6% and 45.4% lower than those of V-free alloy. [ABSTRACT FROM AUTHOR]

Effects of minor Gd addition on the micro-structure, mechanical performance, and corrosion behavior of Mg-1Y alloys were systematically studied. With the addition of increased Gd content, the hydrogen evolution rate of Mg-Y-Gd alloys decreased from 2.0 to 0.5 mm/y. Moreover, the alloying Gd in Mg-Y-Gd alloys leaded to the transformation of the active Mg24Y5 phase into the Mg5(GdY) phase. The high corrosion resistance of Mg-1Y-0.6Gd alloy can be attributed to the fine grain size, uniform distribution of surface potential, and the formation of protective corrosion passivation film rich in Gd2O3 and Y2O3.

Micro-alloying Mg alloys with rare earth elements is an economical and promising way to improve their corrosion resistance. It is of great importance to understand their corrosion behavior for designing corrosion-resistant Mg alloys. In this work, Mg-11Al-0.2Y alloy was prepared for exploring its corrosion behavior in 3.5 wt.% neutral NaCl solution. It exhibits a low corrosion current density of 2.3 µA/cm2 after immersion for 1 d due to the formation of a protective surface film containing Al2O3, MgO and Mg(OH)2. However, nano-scaled pores exhibit at the film/matrix interface, which undermines integrity and protectiveness of the surface film after long-term exposure to chloride solution.

The influence of Al–Mn intermetallic on corrosion resistance of AM50 alloy was investigated. TEM-SAED was utilized to identify microstructure and composition of the corrosion products on Al–Mn intermetallic. The electrochemistry results revealed that the corrosion rate of pure Mg was lower than AM50 due to thermodynamic driving force for micro-galvanic corrosion by Al–Mn with matrix. Although the Volta potential difference reduce because of accumulation of corrosion products, the cathodic activity of AM50 alloy increases with exposure time. The progress of corrosion could not be inhibited since the loose and porous corrosion products provided an area for containing and storing the corrosion medium.

It is well known that the corrosion resistance of ultra-light Mg–Li alloys is inferior to traditional Mg alloys due to the rapid oxidation of reactive Li on the surface. In this study, microalloying Sn has been found to improve the corrosion resistance of Mg–Li alloys due to the formation of Mg2Sn on the corrosion pits and reduction of electro-potential difference. Indeed, the addition of Sn not only reduced the corrosion rate to the minimum value of 4.27 mmpy but also promote the formation of dense corrosion oxide films. The volt potential difference between the matrix (α-Mg and β-Li) and Al-X (Gd, Y, Mn) phases has also been measured to reduce from 260 mV (α-Mg) and 343 mV (β-Li) to 220 mV (α-Mg) and 220 mV (β-Li). After homogenization, pitting was significantly reduced, as shown by the in-situ observation of the corrosion process using X-ray tomography. By quantifying the secondary phases, it has been found that the corrosion expansion was restricted by the Mg2Sn and Al-X phases. The corrosion products are primarily MgO, SnO, and Li2O oxides and the corrosion mechanism follows three stages: I. Breakthrough of MgO protective layer by corrosive fluid; II. Hydrogen evolution reaction (HER) between matrix phase and water immersion; III. Segregation of secondary phases and corrosion products. It has been found that all three processes are highly dependent on the Sn solutes and Mg2Sn precipitates, showing the bright future development of corrosion-resistant Mg–Li alloys by Sn microalloying.

This study investigates the natural passivation process of two types of stainless steels (AISI 316 and AISI 304) and a nickel-based alloy (Inconel 600) as a function of immersion time in an alkaline medium. As shown by Atomic Force Microscopy (AFM), the oxide film growth on each substrate is only influenced by trenches formed during the polishing step and does not depend on the chemical composition. The evolution of EIS measurements is explained by this growth mode. After 3 days of immersion, the formed film constitutes a protective barrier against alloy dissolution, as shown by Scanning Kelvin Probe Microscopy (SKPFM). [ABSTRACT FROM AUTHOR]

The effect of sulfate-reducing bacteria (SRB) on the corrosion behavior of X80 steel welded joint in a soil solution was studied. The results indicated that SRB enhanced the corrosion of X80 steel welded joint. The corrosion behavior in the heat affected zone (HAZ) was quite different from those of in the weld metal (WM) and base metal (BM). The HAZ was an active region that could be preferentially and more quickly corroded. Macro-galvanic corrosion in the welded joint had a significant effect on the MIC behavior of the X80 steel welded joint, leading to the preferential corrosion of the HAZ.

After laser welding, the corrosion resistance and microstructure of a newly developed austenitic stainless steel, QN2109, were investigated. A negligible heat-affected zone was found and the segregation of Cr, Mo, Mn, Ni, and N was revealed by EPMA. In contrast to previously reported findings, the corrosion resistance of δ-ferrite obtained here was lower than that of austenite in acidic solutions revealed by SKPFM and MFM, owing to N segregation. The pitting resistance of whole welds was lower than that of base metal (BM), whereas the pitting resistance of the fusion zone was higher than that of BM, owing to the significant decrease in the number of inclusions.

The mechanics-corrosion and strength-ductility tradeoffs of magnesium (Mg) alloys have limited their applications in fields such as orthopedic implants. Herein, a fine-grain structure consisting of weak anodic nano-lamellar solute-enriched stacking faults (SESFs) with the average thickness of 8 nm and spacing of 16 nm is constructed in an as-extruded Mg96.9Y1.2Ho1.2Zn0.6Zr0.1 (at.%) alloy, obtaining a high yield strength (YS) of 370 MPa, an excellent elongation (EL) of 17%, and a low corrosion rate of 0.30 mm y−1 (close to that of high-pure Mg) in a uniform corrosion mode. Through scanning Kelvin probe force microscopy (SKPFM), one-dimensional nanostructured SESFs are identified as the weak anode (∼24 mV) for the first time. The excellent corrosion resistance is mainly related to the weak anodic nature of SESFs and their nano-lamellar structure, leading to the more uniform potential distribution to weaken galvanic corrosion and the release of abundant Y3+/Ho3+ from SESFs to form a more protective film with an outer Ca10(PO4)6(OH)2/Y2O3/Ho2O3 layer (thickness percentage of this layer: 72.45%). For comparison, the as-cast alloy containing block 18R long period stacking ordered (LPSO) phase and the heat-treated alloy with fine lamellar 18R-LPSO phase (thickness: 80 nm, spacing: 120 nm) are also studied, and the characteristics of SESFs and 18R-LPSO phase, such as the weak anode nature of the former and the cathode nature of the latter (37-90 mV), are distinguished under the same alloy composition. Ultimately, we put forward the idea of designing Mg alloys with high mechanical and anti-corrosion properties by constructing ''homogeneous potential strengthening microstructure'', such as the weak anode nano-lamellar SESFs structure.

The stress-assisted oxidation behaviour of Inconel 52 M/316 austenitic stainless-steel (SS) dissimilar weld joints (DMWJ) in a simulated pressurised water reactor environment was investigated. A corrosion galvanic couple formed between the Inconel 52 M and 316 SS due to differences in their nonferrous metal content. The electric field from the corrosion couple attracted metal cations (e.g. Fe2+, Cr3+) to the Inconel 52 M that were deposited as FeCr2O4. An additional corrosion galvanic couple was generated due to variations in the plastic deformation of the DMWJ. The superposition of electric fields from the different couples resulted in ridge-like oxide depositions in the fusion zone.

The corrosion behavior and mechanism of as-cast, solid-solution treated, and as-extruded Mg-14.4Er-1.4Zn-0.3Zr (wt.%) alloys are investigated. The microstructure characteristic of as-cast alloy, i.e., the semi-continuous 18R-long period stacking ordered (LPSO) phase as cathode with the potential difference (PD) of 83 mV, is the main reason for the relatively strong tendency of micro-galvanic corrosion. The lower micro-galvanic tendency by the decreased size, number, and PD (30 mV) of LPSO-phase particles, and the existence of a few Er3+ in corrosion film, are mainly responsible for the improved corrosion resistance of solid-solution treated alloy. The as-extruded alloy exhibits a superior corrosion resistance (corrosion rate: 1.11 mm y−1 in 3.5 wt.% NaCl solution) as compared to many reported Mg alloys, which mainly attributed to the formation of nano-spaced basal plane solute-enriched stacking faults (SESFs) within fine dynamic recrystallized (DRXed) grains. The nano-scale SESFs as the weak anode with PD of 26 mV weaken the galvanic tendency to form a relatively homogeneously electrochemical microstructure. Moreover, the preferential corrosion of SESFs releases sufficient Er3+, promoting the quasi-passivation state of corrosion film. The construction of weak anodic nano-lamellar SESFs structure within fine grains is a feasible method for the synergetic improvement of strength and corrosion resistance of Mg alloys.

The mechanics-corrosion and strength-ductility tradeoffs of magnesium (Mg) alloys have limited their applications in fields such as orthopedic implants. Herein, a fine-grain structure consisting of weak anodic nano-lamellar solute-enriched stacking faults (SESFs) with the average thickness of 8 nm and spacing of 16 nm is constructed in an as-extruded Mg96.9Y1.2Ho1.2Zn0.6Zr0.1 (at.%) alloy, obtaining a high yield strength (YS) of 370 MPa, an excellent elongation (EL) of 17%, and a low corrosion rate of 0.30 mm y−1 (close to that of high-pure Mg) in a uniform corrosion mode. Through scanning Kelvin probe force microscopy (SKPFM), one-dimensional nanostructured SESFs are identified as the weak anode (∼24 mV) for the first time. The excellent corrosion resistance is mainly related to the weak anodic nature of SESFs and their nano-lamellar structure, leading to the more uniform potential distribution to weaken galvanic corrosion and the release of abundant Y3+/Ho3+ from SESFs to form a more protective film with an outer Ca 10 (PO 4) 6 (OH) 2 /Y 2 O 3 /Ho 2 O 3 layer (thickness percentage of this layer: 72.45%). For comparison, the as-cast alloy containing block 18R long period stacking ordered (LPSO) phase and the heat-treated alloy with fine lamellar 18R-LPSO phase (thickness: 80 nm, spacing: 120 nm) are also studied, and the characteristics of SESFs and 18R-LPSO phase, such as the weak anode nature of the former and the cathode nature of the latter (37-90 mV), are distinguished under the same alloy composition. Ultimately, we put forward the idea of designing Mg alloys with high mechanical and anti-corrosion properties by constructing "homogeneous potential strengthening microstructure", such as the weak anode nano-lamellar SESFs structure. [ABSTRACT FROM AUTHOR]

Non-covalent π-π and dipolar interactions with small aromatic molecules have been widely demonstrated to be a valid option to tune graphene work functions without adding extrinsic scattering centers for charge carriers. In this work, we investigated the interaction between a CVD-graphene monolayer and a thermally evaporated sub-monolayer and the following few-layer thin films of similar perylene diimide derivatives: PDI8-CN2 and PDIF-CN2. The molecular influence on the graphene work function was estimated by XPS and UPS analysis and by investigating the surface potentials via scanning Kelvin probe force microscopy. The perfluorinated decoration and the steric interaction in the early stages of the film growth determined a positive work function shift as high as 0.7 eV in the case of PDIF-CN2, with respect to the value of 4.41 eV for the intrinsic graphene. Our results unambiguously highlight the absence of valence band shifts in the UPS analysis, indicating the prevalence of dipolar interactions between the graphene surface and the organic species enhanced by the presence of the fluorine-enriched moieties. [ABSTRACT FROM AUTHOR]

A detailed microstructural and electrochemical analysis of electroless nickel phosphorous (NiP) coatings with P contents of 13.2 ± 1.2 wt%, 12.9 ± 0.7 wt%, and 8.3 ± 0.8 wt% on a copper substrate was performed to study the corrosion behaviour of electroless NiP/Cu systems. The P content of the electroless NiP coatings plays an essential role in the microstructure of the coatings in terms of crystallinity. The crystallinity variations, representing the extent of crystalline and amorphous phases within the material, with P content, affect the local electrochemical characteristics and, hence, the corrosion protection behaviour of electroless NiP coatings. The coatings with the highest P content showed the best corrosion performance in a 3.5 wt-% NaCl solution. In contrast, the surface of the electroless NiP coatings with low P content is more susceptible to corrosion due to the presence of locations with heterogeneous electronic properties that initiate localised corrosion. Microgalvanic interactions with a high cathode-to-anode surface ratio govern the localised corrosion kinetics of the low P-content samples. A high concentration of nodule boundaries and/or other existing structural defects on the surface serve as anodic sites, whereas the remainder of the surface serves as cathodic sites. • P content influences the localised corrosion mechanism of electroless NiP coatings. • P contents are associated with changes in NiP microstructure and topography. • Electrochemical and microstructural analyses offer insight into the corrosion mechanism. [ABSTRACT FROM AUTHOR]

This study investigates the natural passivation process of two types of stainless steels (AISI 316 and AISI 304) and a nickel-based alloy (Inconel 600) as a function of immersion time in an alkaline medium. As shown by Atomic Force Microscopy (AFM), the oxide film growth on each substrate is only influenced by trenches formed during the polishing step and does not depend on the chemical composition. The evolution of EIS measurements is explained by this growth mode. After 3 days of immersion, the formed film constitutes a protective barrier against alloy dissolution, as shown by Scanning Kelvin Probe Microscopy (SKPFM).

Non-covalent π-π and dipolar interactions with small aromatic molecules have been widely demonstrated to be a valid option to tune graphene work functions without adding extrinsic scattering centers for charge carriers. In this work, we investigated the interaction between a CVD-graphene monolayer and a thermally evaporated sub-monolayer and the following few-layer thin films of similar perylene diimide derivatives: PDI8-CN2 and PDIF-CN2. The molecular influence on the graphene work function was estimated by XPS and UPS analysis and by investigating the surface potentials via scanning Kelvin probe force microscopy. The perfluorinated decoration and the steric interaction in the early stages of the film growth determined a positive work function shift as high as 0.7 eV in the case of PDIF-CN2, with respect to the value of 4.41 eV for the intrinsic graphene. Our results unambiguously highlight the absence of valence band shifts in the UPS analysis, indicating the prevalence of dipolar interactions between the graphene surface and the organic species enhanced by the presence of the fluorine-enriched moieties.

The microstructure of multi-component Mg-Li alloys played a decisive role in their corrosion properties due to the potential differences between the matrix and the secondary phases. In this study, the effects of secondary phases (AlLi, AlX(Gd, Y, Mn), and Mg 2 Sn) on the corrosion behavior of Mg-Li alloys have been quantified by using in situ X-ray CT. The microstructure-property correlation was established between the type, morphology, distribution, and dimensions of the secondary phases and the microscopic corrosion behavior. The corrosion parameters, such as average equivalent diameter, distance, number density, and volume fraction of the secondary phases and corrosion pits, were quantified as a function of corrosion time. The dominating secondary phase was identified by combining SKPFM analysis and electrochemical testing, giving quantitative information on corrosion control by designing secondary phases. [Display omitted] • Corrosion occurred preferentially in the vicinity of AlLi due to its larger potential. • Characterization of the surface potential of the secondary phase by SKPFM. • Quantifying the correlation between the secondary phase and corrosion. • AlX and Mg 2 Sn serve as corrosion barriers during the pre-corrosion period. • Mg-Li alloy exhibited excellent anti-corrosion during corrosion immersion for 72 h. [ABSTRACT FROM AUTHOR]

The effect of the Ca2Mg6Zn3 phase on the corrosion behavior of biodegradable Mg-4.0Zn-0.2Mn-xCa (ZM-xCa, x = 0.1, 0.3, 0.5 and 1.0 wt.%) alloys in Hank’s solution was investigated with respect to phase spacing, morphology, distribution and volume fraction. With the increase in Ca addition, the volume fraction of the Ca2Mg6Zn3 phase increased from 2.5% to 7.6%, while its spacing declined monotonically from 43 μm to 30 μm. The Volta potentials of secondary phases relative to the Mg matrix were measured by using scanning kelvin probe force microscopy (SKPFM). The results show that the Volta potential of the intragranular spherical Ca2Mg6Zn3 phase (+109 mV) was higher than that of the dendritic Ca2Mg6Zn3 phase (+80 mV). It is suggested that the Ca2Mg6Zn3 acted as a cathode to accelerate the corrosion process due to the micro-galvanic effect. The corrosion preferred to occur around the spherical Ca2Mg6Zn3 phase at the early stage and developed into the intragranular region. The corrosion rate increased slightly with increasing Ca content from 0.1 wt.% to 0.5 wt.% because of the enhanced micro-galvanic corrosion effect. The decrease in the phase spacing and sharp increase in the secondary phase content resulted in a dramatic increase in the corrosion rate of the ZM-1.0Ca alloy.

This study elucidates the effect of cold rolling on the microstructure, corrosion and electrochemical response of the lean duplex stainless steel LDX 2101®. With thickness reductions of 0%, 20% and 40%, three different specimens are investigated in terms of microstructure (electron backscattered diffraction [EBSD] and energy‐dispersive X‐ray spectroscopy [EDS]), corrosion properties (ASTM G150, ASTM G61 and field testing), passive film properties (X‐ray photoelectron spectroscopy) and electrochemical response (scanning Kelvin probe force microscopy [SKPFM]). It is shown that deformation of LDX 2101 leads to changes in the microstructure such as mechanical twinning and martensite formation. The combination of EBSD, EDS and SKPFM maps shows that the work function is clearly dependent on composition, deformation and local misorientation, but not on the crystallographic orientation of the grains in the microstructure. Zones with low work function are seen to have the highest pitting susceptibility, which includes deformed ferritic, martensitic phase and areas with a high concentration of dislocations such as grain boundaries and mechanical twins. The overall conclusion is that cold deformation up to a 40% thickness reduction has a significant influence on the microstructure, but a small impact on the corrosion resistance of LDX 2101. [ABSTRACT FROM AUTHOR]

The microstructure, hardness and corrosion behavior of CoCrFeNiSn x (x = 0, 0.1, 0.5 and 1.0) HEAs were investigated in this work. The increase of the Sn addition resulted in the improvement of hardness (reached 424.9 HV) which attributed to the increase of the Ni 3 Sn 2 phase with higher hardness. Adding Sn with molar ratio of 0.1 promoted the pitting initiation due to the potential difference between the two phases. CoCrFeNiSn 0.5 and CoCrFeNiSn 1.0 exhibited enhanced corrosion resistance compared to the alloy without Sn, which ascribed to the increase in cathode area (Ni 3 Sn 2 phase) leading to a decrease in pitting sensitivity of FCC phase. • The hardness and corrosion behavior of CoCrFeNiSn x high entropy alloys in NaCl solution were investigated. • CoCrFeNiSn 0.5 and CoCrFeNiSn 1.0 demonstrated superior hardness and corrosion resistance. • The mechanisms behind the corrosion performance of CoCrFeNiSn x high entropy alloys were assessed. [ABSTRACT FROM AUTHOR]

• Passive film of M13Cr becomes more defective after 75 °C in CO 2 -Cl brines. • Cr and Mo enrichment in the passive film contribute to corrosion resistance. • Ti(C,N) serves as pit initiation sites from Cr/Mo depletion and SKPFM results. • Ti(C,N) are anodic which contradicts previous claims of cathodic behavior. • Temperature increases soluble CrO 3 , reducing film repassivation capabilities. The influence of temperature (25, 75, and 150 °C) on the passivation behavior of Modified Martensitic 13Cr Stainless Steel (M13Cr) in CO 2 saturated acidic salt brine environments was investigated. The material was found to contain Ti(C,N) inclusions and Volta potential maps obtained through scanning Kelvin probe force microscopy (SKPFM) identified them to be more anodic (60 mV lower) than the matrix. Cyclic polarization (CP) showed a shift in pitting and repassivation potentials to more negative values at higher temperatures. Electrochemical impedance spectroscopy (EIS) and Mott–Schottky tests showed that the passive film formed was more defective with increasing temperature. X-ray photoelectron spectroscopy (XPS) confirmed the presence of a defective passive film with reduced repassivation capabilities due to higher contents of soluble CrO 3 /Cr6+ species at temperatures exceeding 75 °C. These results offer valuable insights into understanding the pit initiation mechanisms and performance of M13Cr. [Display omitted] [ABSTRACT FROM AUTHOR]

The variation rule of the Volta potential on deformed copper surfaces with the dislocation density is determined in this study by using electron back-scattered diffraction (EBSD) in conjunction with scanning Kelvin probe force microscopy (SKPFM). The results show that the Volta potential is not linear in the dislocation density. When the dislocation density increases due to the deformation of pure copper, the Volta potential tends to a physical limit. The Volta potential exhibits a fractional function relationship with the dislocation density only for a relatively low shape variable.

The paper aims at characterizing the influence of intermetallic compounds on the corrosion localization of innovative Al–Si–Mg Er‐ and Zr‐containing casting alloys. Samples of the investigated materials were studied by means of optical and scanning electron microscope micrographs, immersion tests, and scanning Kelvin probe force microscope (SKPFM) analyses in the T6 temper. Combination of immersion tests and SKPFM analyses allowed to identify those classes of intermetallic compounds promoting localization of the corrosion process. It was found that intermetallic compounds richer in Fe were the most critical for corrosion localization; furthermore, additions of Er caused a marked decrease of the potential difference of intermetallic compounds with respect to the Al matrix and a consequent less intense microgalvanic coupling, which translates into slower corrosion kinetics. Further, Zr additions slightly increased the potential difference of intermetallic compounds with the Al matrix, promoting a faster corrosion process. [ABSTRACT FROM AUTHOR]

• Local electrochemical properties of fusion boundary were studied by combining capillary and photolithographic mask technique. • Martensite in fusion boundary area shows passivation behavior and better corrosion resistance in 3.5 wt% NaCl solution. • A controversy was demonstrated between the nobility prediction through SKPFM test and local electrochemical measurements. The 309 L-SA508 fusion boundary (FB) in a SA508−309 L/308 L overlay cladding weldment was characterized by multi-analytical approaches. Local electrochemical properties around the FB region were investigated in 3.5 wt% NaCl solution by utilizing a self-developed microcell setup combining lithography and capillary techniques. The corrosion resistances follow the order: P1 (little austenite + martensite)>P2 (martensite + little coarse ferrite)>P3 (martensite + numerous coarse ferrite)>P4 (coarse ferrite). A better corrosion resistance of P1 is attributed to its higher Cr, Ni content and larger proportion of Σ3 boundaries. The controversy between results of scanning Kelvin probe force microscopy and local electrochemical measurements was demonstrated. [ABSTRACT FROM AUTHOR]

Abstracts The role of long period stacking ordered (LPSO) structure in the corrosion behavior of Mg-Gd-Zn-Zr alloys was investigated by means of potentiodynamic polarization experiments, hydrogen evolution tests, and microstructure characterization. The corrosion rate of the Mg-Gd-Zn-Zr alloys is mainly determined by the acceleration effect of the second phases in the micro-galvanic corrosion. After T4 heat-treatment, the β-(Mg,Zn) 3 Gd eutectic phase in the as-cast Mg-Gd-Zn-Zr alloys transforms into an X phase with a 14H-LPSO structure. According to the results of scanning Kelvin probe force microscopy (SKPFM), the potential difference between LPSO phase and the α-Mg matrix is 243 mV, whereas, it is 290 mV between the eutectic phase and matrix in the as-cast alloys. The low relative potential and volume fraction of the LPSO phase reduce the acceleration degree of micro-galvanic corrosion. As a result, the corrosion resistance of Mg-Gd-Zn-Zr alloys improves significantly by the LPSO structure. Highlights • Corrosion rate of T4 treated alloys with LPSO structure is extremely lower than as-cast alloys without LPSO structure. • Micro-galvanic corrosion dominates the corrosion behavior of Mg-Gd-Zn-Zr alloys. • LPSO phase can improve the corrosion resistance of Mg-Gd-Zn-Zr alloys significantly due to its lower potential. [ABSTRACT FROM AUTHOR]

Abstract The relative potential difference can be treated as an index of local corrosion of alloys. Since local corrosion is driven by the micro-galvanic coupling, which is consist of the micro-constituent phases and the matrix. They present distinct potential difference normally. In the present work, the relationship between the Volta potential and the corrosion effect of the dominated intermetallic phase in the AZ91 Mg alloy with (La, Ce) MM addition was investigated. A multiscale approach coupling global and local measurements was used to study the corrosion behavior of the alloy and its intermetallic phase. Results showed that the microstructure of AZ91 Mg alloy with (La, Ce) MM addition was complex, with the presence of Al 4 (La, Ce) phases in acicular or rod shape, a small number of Al 8 Mn 4 Ce, β-Mg 17 Al 12 and α-Mg solid solution. In this case, the improved corrosion resistance of the alloy was achieved. Scanning Kelvin probe force microscopy (SKPFM) analysis revealed that all the intermetallics were noble comparing with the α-Mg solid solution. In-situ electrochemical atomic force microscopy (EC-AFM) observation for the initial stages of corrosion showed the α-Mg matrix surrounded by β-Mg 17 Al 12 or Al 8 Mn 4 Ce was susceptible to pitting corrosion. No noticeable corrosion occurred at the α-Mg adjacent to Al 4 (La,Ce) phase, in spite of the relatively higher difference of Volta potential between Al 4 (La,Ce) phase and the matrix. Volta potential is insufficient to determine whether the phase is an effective cathode or anode. Highlights • Corrosion of (La,Ce) alloyed AZ91 was studied using Å-nm-μm multiscale methods. • Al 4 (La,Ce) exhibited the highest potential in all intermetallics. • Al 4 (La,Ce) presented a limited effect on the micro-galvanic corrosion damage. • Geometric shape of intermetallics has influence on the micro-galvanic corrosion. [ABSTRACT FROM AUTHOR]

Highlights • Cerium malate was synthesized. • The corrosion inhibition on Al 2 Cu-Al 2 CuMg-Al, Al 2 CuMg-Al and Al 2 Cu-Al was studied. • Cerium malate is effective in corrosion inhibition of AA 2024-T3. Abstract A new corrosion inhibitor, cerium malate, was synthesized. Its inhibiting behaviour on coupled Al 2 Cu-Al 2 CuMg-Al, Al 2 CuMg-Al and Al 2 Cu-Al was studied. Cerium malate is effective in corrosion inhibition of the three coupled systems. The inhibition mechanism of cerium malate on pitting corrosion of Al 2 CuMg and Al 2 Cu phases in AA 2024-T3 was analyzed by scanning vibrating electrode technique (SVET), atomic force microscopy (AFM) and scanning kelvin probe force microscopy (SKPFM). The results indicate that cerium malate has good inhibiting effect on AA 2024-T3. [ABSTRACT FROM AUTHOR]

Highlights • Mg-2Zn-0.6Zr-xNd alloys were designed to obtain different second phases. • Nd-containing T phases acted as micro-anodes in galvanic corrosion. • Corrosion mechanism during degradation process in SBF was discussed. Abstract A complete understanding of the role of Mg-Zn-Nd (T) phase in surface micro-galvanic corrosion of Mg alloys has not been fully developed. Therefore, the microstructure evolution and corrosion behavior in simulated body fluid (SBF) of Mg-2Zn-0.6Zr-xNd alloys (x = 0, 0.2, 0.6 and 1 wt%) were investigated. It was found that the MgZn phase in Mg-2Zn-0.6Zr alloy changed to Mg 60 Zn 32 Nd 8 (T 2) and Mg 35 Zn 40 Nd 25 (T 3) phases after adding 0.2–1 wt% Nd. With the formation of T phases, the grain size increased first and then decreased. By using scanning kelvin probe force microscopy (SKPFM), the Volta potentials of second phases relative to Mg matrix were measured. T 2 and T 3 phases with a relative Volta potential of about −400 mV acted as micro-anodes, so that they were corroded preferentially during the corrosion process. Because of the appropriate amount of anodic T phases and their discontinuous distribution, the alloy with 0.2 wt% Nd addition showed a uniform surface corrosion characteristic and exhibit the best corrosion resistance. [ABSTRACT FROM AUTHOR]

Microscopic aspects of electrochemical reactions in a B10 Cu-Ni alloy/2205 duplex stainless steel (DSS) galvanic couple immersed in NaCl solution were investigated by electrochemical noise (EN) technique, scanning kelvin probe force microscopy (SKPFM), scanning vibrating electrode technology (SVET) as well as by scanning electron microscopy (SEM) method. Wavelet analysis by EN technique and microscopic characterization showed that the galvanic corrosion process can be divided into five detail stages. SKPFM and SEM observations revealed that the B10 Cu-Ni alloy/2205 DSS is a small-scale B10/ferrite/austenitic galvanic corrosion system that reduces the resistance of 2205 DSS to pitting attack. • Galvanic corrosion of Cu-Ni alloy/2205 DSS couple was analyzed. • Pitting corrosion was observed on the surface of cathodic 2205 DSS in the galvanic system. • The galvanic corrosion process can be divided into five stages by wavelet analysis. • More accurate corrosion mechanism can be revealed by EN analysis. [ABSTRACT FROM AUTHOR]

• The addition of Cu reduces the corrosion resistance of the A356 aluminum alloy. • The number and size of pores in A356 cast aluminum alloys increases with the increase in the content of the metal element Cu. • Corrosion of the alloy occurs mainly in the non-precipitated regions at the edges of the Al 2 Cu particles and Si particles. In this article, the pore and precipitation phases of A356 aluminum alloy were regulated by adding element Cu, and the corrosion kinetic behavior was investigated by electrochemical experiments and salt spray test (SST), while the corrosion mechanism of A356 aluminum alloy was studied by scanning electron microscopy (SEM), 3D laser confocal microscopy (LSCM) and atomic force microscopy (SKPFM). The results of both electrochemical and salt spray experiments showed that the corrosion rate increased with increasing Cu content, and the average corrosion rate increased from 0.040 mm y-1 to 0.329 mm y-1 when the Cu content increased from 0 wt% to 7 wt%, and the Cu free alloy exhibited a greater charge transfer resistance. This is mainly due to the addition of Cu on the one hand to increase the number of precipitation phase, Al 2 Cu become the main precipitation phase, SKPFM test results show that the precipitation phase relative to the Al matrix potential difference in order: Al 2 Cu (350 ∼ 380 mV), Si (250 ∼ 275 mV), Mg 2 Si (80 ∼ 110 mV), the increase in potential difference between the two phases to promote the corrosion of occurrence. On the other hand, CT results showed that the average diameter of pores increased from 89.95 µm to 281.00 µm, and the volume fraction increased from 0.05 % to 0.18 %, and the larger and more porous pores help promote corrosion. Therefore, how to control the porosity and precipitation phase is an important factor in regulating the corrosion behavior of A356 aluminum alloy. [ABSTRACT FROM AUTHOR]

The corrosion behavior of a new Nb-doped stainless steel (SDSS-Nb) designed by the CALPHAD method, produced using an open atmosphere process based on recycled materials, was investigated to improve the circular economy. Three heat-treatment conditions were evaluated to assess the sensitization effects of the precipitates and inclusions. XRD and SEM-EDS were used for phase identification, and sensitization was analyzed by cyclic polarization and Scanning Kelvin Probe Force Microscopy (SKPFM). The thermodynamic stability predicted by Thermo-Calc agrees with that observed by SEM-EDS. It was observed by cyclic polarization that the corrosion sensitization was mainly provided by the σ phase, which was deduced from the results obtained by SEM-EDS, XRD, and Thermo-Calc simulations. Furthermore, it was obtained that the sensitization due to Cr 2 N precipitates and nonmetallic inclusions was low, and the mechanical response is comparable to commercial UNS32750 super duplex stainless steel, which allows a good performance in severe environments and an efficient industrial application. Additionally, it has been obtained by SKPFM that the shear potential between the σ phase and the austenite is between 210 mV and 241 mV and that its value depends on the stability and equilibrium reached by the σ phase during thermal cycling. • Novel Nb-doped SDSS was designed produced at open-air with recycled materials. • The response to corrosion with annealing treatment on the new SDSS-Nb was analyzed. • The Cr2N and inclusions do not generate significant corrosion damage in the new SDSS. • The mechanical and corrosion response of the new SDSS are suitable for industrial use. [ABSTRACT FROM AUTHOR]

This study investigates the effects of adding different amounts of Mg to the surface of pure Al substrate using friction stir processing (FSP) technique to prepare Al–Mg solid solutions. For this purpose, machined grooves on the surface of the pure Al plates were filled by bulk Mg blocks and FSPed to form Al–Mg solid solution layers with ∼2.0, 4.5, and 33.9 at.% Mg. The chemical composition, microstructure, and surface Volta potential of the surface alloyed layers were studied by SEM/EDS, XRD, and SKPFM, respectively. The results revealed that incorporating Mg into the Al substrate causes a considerable refinement of the microstructure, resulting in a significant increase in Vickers hardness number from 25 to 208.4 HV (∼734% increase). As the Mg content in the alloyed layer increased, a transition from a single-phase solid solution structure to a dual-phase structure was observed. Based on the potentiodynamic polarization results, it is evident that the corrosion resistance of the single-phase alloyed layer can match that of marine-grade aluminum alloys. • Al–Mg alloyed layers with different Mg content were fabricated by FSP. • Low Mg samples are essentially single phase while high Mg sample is dual phase. • Increasing Mg in the stirred zone, refines structure and increases hardness. • Single phase samples show corrosion resistance comparable to marine Al–Mg alloys. [ABSTRACT FROM AUTHOR]

Herein, we investigated the effects of Ce on the corrosion behavior of NdFeB magnets in 3.5% NaCl solutions using electrochemical tests, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) mapping, and scanning Kelvin probe force microscopy (SKPFM). We demonstrated that Ce markedly enhances the corrosion resistance of NdFeB magnets. Ce primarily replaces Nd in the Nd-rich phase instead of matrix phase, increasing the surface potential of the Nd-rich phase. An increase in the Ce content from 0 to 5.21 wt%, decreased the potential difference between the main phase and (Nd, Ce)-rich phase from 350.2 mV to 97.7 mV; therefore, the corrosion resistance of the magnetic materials increased. The corrosion resistance constituted the Nd-rich phase < the void < metal matrix. Moreover, based on the results of the study, we discussed the impact mechanism of additions of Ce on the corrosion resistance of the magnets.