Worse Corrosion Resistance Research Articles

Effect of Bias Arc on Microstructure and Corrosion Resistance of Q235/304 Dissimilar-Steel-Welded Joints.

To fully exploit the advantages of steel, the welding connection of dissimilar steels has been developed. In this work, the metallographic microstructures, elemental distributions, and electrochemical corrosion properties of the Q235 and 304 welds under different bias arcs were investigated. The arc bias caused the Q235-side heat-affected zone to widen, the microstructure consisted of ferrite and pearlite, and the ratio varied with decreasing distance from the fusion line. Elemental scans show that Cr and Ni concentration gradients exist near the fusion line. The 304-stainless-steel-side heat-affected zone was mainly composed of austenite grains, and the fusion zone was narrower but prone to cracking. Electrochemical tests revealed that 304 stainless steel had the best corrosion resistance, while Q235 had the worst corrosion resistance, and that the welded joints with an arc bias toward the 304 side had the best corrosion resistance. The samples' the passivation film which formed via electrochemical polarization had limited stability, but the over-passivation potential could be used as a reference for corrosion resistance. Overall, the arc bias and weld material properties significantly affected the microstructure and corrosion resistance of the joints.

Comparative study on microstructure and properties of HR-2 anti-hydrogen steel weld joints with different section shapes by vacuum electron beam welding

The forming, microstructure, mechanical properties and corrosion resistance of three kinds of vacuum electron beam welded joints with different shapes were studied. The results of X-ray inspection of the joints showed that the three shapes of welded joints could meet the requirements of the quality inspection. The results of microstructure characterization show that the worm or bone-like δ-ferrite appears in the upper and lower regions of the funnel-shaped and bell-shaped joints, while only a small amount of δ-ferrite appears in the local regions of the nail-shaped joints. The test results of mechanical properties show that the micro-hardness of the weld center in the three kinds of shaped joints is the lowest. All the specimens fracture in the weld, and the bell-shaped weld presents the highest impact energy and bending load. Funnel-shaped weld shows the worst corrosion resistance due to the element segregation of the weld. Thus, the bell-shaped joint exhibits the best comprehensive performance.

Corrosion properties and mechanism of Ti43Zr27Mo5Cu10Be15 amorphous composites in various conditions

The in situ Ti43Zr27Mo5Cu10Be15 amorphous composites were investigated for their corrosion properties in solutions of NaCl, HCl, H2SO4 and NaOH. Electrochemical testing, SEM, EDS and XPS analyses revealed that pitting in NaCl and HCl solutions caused local surfaces damage. Amorphous matrix corrodes slightly in H2SO4 solution. Uniform corrosion occurred in NaOH solution without passive film formed, leading to the worst corrosion resistance. The optimal corrosion performances for NaCl and HCl solution are achieved at 0.5 mol l−1 and 0.75 mol l−1 separately which is related to the shortage of oxygen content in the solutions. While, the best corrosion performances for H2SO4 and NaOH solution are at 0.25 mol l−1. Moreover, the research on the effect of temperature was conducted in 3.5 wt% NaCl solution, it was found that Ti43Zr27Mo5Cu10Be15 amorphous composites exhibited good corrosion resistance at 298 K, while the E corr declined with increasing solution temperature.

Effect of Mo content on microstructure and corrosion behavior in HCl of ultra-high strength maraging steels

Maraging steels are one of the highest strength steels commercially available. The new versions are known as ultra-high strength maraging (UHSM) steels and can offer yield strength values over 3 GPa. The aim of this investigation was evaluating the electrochemical behavior of three non-commercial/laboratory UHSM steels containing 13Ni–15Co and Mo content variations (7.5, 11 and 15 wt%). The UHSM steels were annealed at 1000 °C and studied at different conditions (non-aged and aged at 480 °C for 3 h and 6 h). As reference material, a commercial maraging steel (18Ni–9Co–5Mo) heat treated according to typical recommendations (annealed at 820 °C for 1 h and aged at 480 °C for 4 h) was used. The UHSM presented considerable higher hardness than commercial maraging. Comparing between the UHSM steels, the samples treated for 6 h do not contribute to increase the hardness when compared to those of 3 h. The electrochemical tests in hydrochloric aqueous solution showed that commercial maraging steel and the UHSM containing most Mo (11 wt%) aged by 6 h presented the worst corrosion resistance while the best performance was obtained by the samples with 7.5 and 11 wt% Mo aged for 3 h.

A promising perspective in improving corrosion and wear resistance of plain steel through electrodeposition of thick Ni–Mo–W ternary alloy

In this study, thick Ni–Mo–W ternary alloy coatings (∼24 μm) with 13–27 wt% Mo and 4–11 wt% W were electrodeposited from an alkaline citrate-ammonia bath using direct current. The effect of current density (20–100 mA/cm2) on the composition, current efficiency, morphology, structure, surface topography, tribological behavior, and corrosion resistance of coatings was investigated. The findings revealed an advantageous induced co-deposition of Mo in an electrolyte containing equimolar Mo and W ions. While increasing the current density decreased the Mo content of the coatings, they always had more Mo than W. Increasing the current density, according to SEM and AFM observations, changed the smooth and nodular morphology of Ni–Mo–W coatings to a relatively rough and cauliflower shape. The microhardness of the produced nanocrystalline solid solution coatings was 3.8–4.9 times higher than that of the plain carbon steel substrate. While the hardest coating (793 Hv) deposited at 100 mA/cm2 had the best wear resistance with a volume loss value of 0.04 mm3, it had the worst corrosion resistance among the coatings with icorr = 4.4 μA/cm2. The least hard coating (607 Hv), deposited at 40 mA/cm2, with the highest wear volume loss value of 0.11 mm3, however, was the most corrosion resistant sample with icorr = 1.9 μA/cm2.

Corrosion behavior of steel exposed to "zero" pollution atmosphere environment for 20 years

In this study, the corrosion behavior of Q235 carbon steel, 09CuPTiRE weathering steel and X60 pipeline steel after 20 years exposure in "zero" pollution atmosphere environment was investigated by corrosion rate analysis, macroscopic observation, scanning electron microscopy, X-ray diffraction, white light interferometers and electrochemical analysis were conducted to analyze. The results showed that the corrosion rate of the three kinds of steels increases first and then decreases with time, and the results indicated that the empirical formula D=Atn was suitable for corrosion kinetics of three materials, and the three kinds of steels all form a relatively dense rust layer, which can effectively protect the metal matrix, inhibit the corrosion process and reduce the rate of corrosion. Under the same exposure time and the same corrosion conditions, the corrosion degree of the three materials is: X60 pipeline steel > Q235 Carbon steel >09CuPTiRE Weathering steel, three kinds of steel corrosion products are the same, only α-FeOOH and γ-FeOOH exist in the rust layer, and the relative content of α-FeOOH is more than γ-FeOOH of each steel in both skyward side and fieldward sides. X60 Pipeline steel has the worst corrosion resistance, and 09CuPTiRE weathering steel has the best corrosion resistance, so 09CuPTiRE weathering steel has better adaptability to this environment.

Effect of Scanning Strategy on the Manufacturing Quality and Performance of Printed 316L Stainless Steel Using SLM Process.

In this study, the effects of Z-0°, Z-67°, Z-90°, I-67°, and S-67° scanning strategies on the surface morphology, microstructure, and corrosion resistance of the specimens in SLM316L were systematically studied. The results show that the partition scanning path can effectively improve the manufacturing quality of the specimen, reduce the cumulative roughness layer by layer, and increase the density of the specimen. The scan path of the island partition of the fine partition is better than that of the strip partition; moreover, the 67° rotation between each layer reduces the accumulation of the height difference of the melt pool, fills the scanning gap of the previous layer, and improves the molding quality of the sample. Electrochemical tests were performed in an aqueous solution of NaCl (3.5 wt%), including open-circuit potential (OCP), dynamic potential polarization, and electrochemical impedance spectroscopy (EIS). The results show that the specimen with a 67° rotation between each layer achieves stability of the surface potential in a short time, and the I-67° specimen exhibits good corrosion performance, while the Z-0° specimen has the worst corrosion resistance.

Effect of low concentration electrolytes on the formation and corrosion resistance of PEO coatings on AM50 magnesium alloy

In this paper, the formation process, morphology, and electrochemical performance of PEO coatings on AM50 magnesium alloy prepared in low concentration phosphate, aluminate, and phosphate-aluminate electrolytes were systematically studied. The results show that the coatings prepared from the phosphate electrolytes have a higher thickness and better corrosion resistance properties compared to the other electrolytes. The coatings prepared from low concentration phosphate-aluminate mixed electrolytes have slightly thinner thickness, a similar coating structure and an order of magnitude lower value of electrochemical impedance compared with phosphate electrolyte coatings. The Coatings prepared from low concentration aluminate electrolytes have the lowest thickness and the worst corrosion resistance properties which gets close to corrosion behavior of the bare AM50 under the same test conditions. Considering application, coatings prepared from single low concentration phosphate electrolytes and low concentration phosphate-aluminate electrolytes have greater potential than single low concentration aluminate coatings. However, reducing the electrolyte concentrations of coating forming ions too much has negative influence on the coating growth rate.

Corrosion behavior of iron-based and Ni-based alloys melted in NaCl–MgCl2–KCl mixed molten salt under vacuum atmosphere

In this work, static immersion and gravimetric methods were used to study the corrosion behavior of three common stainless steels and four Ni-based alloys in a NaCl–MgCl2–KCl mixed molten salt under vacuum atmosphere. The corrosion test was conducted at 700 °C, with a maximum exposure time of 100 h. Corrosion behavior was determined by measuring the mass loss of the sample at different time intervals and the corrosion rates at 100 h. The microstructure of the alloy was analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), atomic force microscope (AFM), and X-ray diffraction (XRD). The results showed that stainless steels were generally more severely corroded than Ni-based alloys. 304 stainless steel and In800H exhibited the worst corrosion resistance, whereas Ni-based alloy In625 had the best corrosion resistance. Fe and Cr were dissolved in the molten chloride salts and reacted with the molten chloride salts. Mo played a positive role in suppressing the corrosion of the alloys in molten chloride salts by inhibiting the outward diffusion of the elements.

Investigation on mechanical properties and corrosion behavior of dissimilar joints of 5083 and 6005A alloy welded by friction stir welding

AbstractIn this paper, the microstructure, mechanical properties, and corrosion behavior of friction stir welded (FSW) joints of the two aluminum alloys 6005A‐5083 were investigated and their correlation was discussed. In contrast to FSW joints of the same aluminum material, this results in a “V” shape curve of hardness distributed nonsymmetrically along the weld. The lowest hardness area occurs at the interface between the heat‐affected zone and the thermo‐mechanically affected zone of 6005A (6‐HAZ and 6‐TMAZ) due to the transformation of the β" phase under the influence of heat input during the stir friction process. This also leads to all tensile specimens fracturing in this area. The corrosion behavior of the FSW joint in acidic solution containing Cl− was determined by an exfoliation corrosion (EXCO) test, an intergranular corrosion (IGC) test, and potentiodynamic polarization measurements, based on the potential application in acid rain environment. The results showed that the corrosion resistance order in the acidic solution is: 6‐HAZ > NZ > 6‐BM > 5‐HAZ > 5‐BM. The 5‐BM has the worst corrosion resistance due to the high corrosion sensitivity of Al3Mg2 in acidic solution. However, good corrosion resistances are shown in NZ and 6‐HAZ, which is related to a relatively homogeneous microstructure in NZ and a dissolution or coarsening of β" phases in 6‐HAZ because of frictional heat input.

CO2 Corrosion of X80 Steel under High Shear Flow Fields

Corrosion failure accidents owing to flow erosion and pipeline corrosion frequently occur during transportation. In this study, a high wall shear stress (WSS) experimental setup was established to conduct the online electrochemical corrosion test. The corrosion behavior of welded joints in NACE solution was studied by electrochemical experimental methods such as electrochemical impedance spectroscopy (EIS) and wire harness microelectrode (WBE). The results show that different areas of the welded joint show different corrosion phenomena in NACE solution. The weld metal (WM) has the significantly better corrosion resistance, while the base metal (BM) and heat-affected zone (HAZ) have worst corrosion resistance than WM. The current of the WM surface was cathodic current, while the current of the BM and HAZ surface were anode currents.

Corrosion Resistance Enhancement of Selective Laser Melted Cost‐Effective Interstitial Medium‐Entropy Alloy via Deep Cryogenic Treatment

An economically interstitial FeMnCrNiCu medium‐entropy alloy (MEA), which exhibits preferable corrosion resistance in 3.5 wt% NaCl solution, is fabricated by selective laser melting (SLM). Compared with annealing, which is one of the posttreatments for additive manufacturing, deep cryogenic treatment (DCT) also contributes significantly to the alloy properties and is expected to improve corrosion resistance. Herein, the corrosion behavior of SLM‐MEA after DCT in 3.5 wt% NaCl solution is investigated. DCT improves corrosion resistance by promoting the uniform distribution of precipitates in SLM‐MEA and changing the cation ratio in the passive film. After DCT, the corrosion current density of the SLM‐MEA in original and annealed state decreases by 27.07% and 62.69%, respectively. The annealed SLM‐MEA exhibits the worst corrosion resistance as a result of the precipitation of continuous Cr‐rich M23C6 carbides at grain boundaries. The face‐centered cubic structure of MEA does not change after annealing or DCT. Significantly, the number, size, and distribution of the precipitates are greatly affected. DCT after annealing promotes the uniform diffuse distribution of M23C6 carbides and nanoscale Cu‐rich particles while increasing the Cr+Ni/Fe+Mn ratio in the passive film, resulting in a significant improvement in corrosion resistance.

Improved Corrosion and Long‐Term Immersion Behavior in 3.5 wt% NaCl Solution of Laser Powder Bed Fusion Produced Ti5Cu After Heat Treatment

This work investigates the corrosion behavior and mechanism of laser powder bed fusion produced (LPBFed) Ti5Cu and its heat‐treated counterparts in 3.5 wt% NaCl solution. The results indicate that heat treatment can enhance the corrosion resistance of LPBFed Ti5Cu by generating Ti2Cu phase, and heat treatment at higher temperature enhances corrosion resistance by forming a stable oxide film with a lower electron diffusion rate. The existence of Ti2Cu phase in the heat‐treated sample acts as the microanode that decelerates the corrosion on α‐Ti phase (prior dissolution of Ti2Cu phase). The long‐term immersion test results also confirm that the Ti2Cu phase present in HT900 (at higher heat‐treatment temperature) provides a better protective effect against corrosion compared to the one in HT740 and as‐LPBFed samples. Compared with the heat‐treated counterparts, the worst corrosion resistance of the as‐LPBFed Ti5Cu is attributed to that the acidic environment (e.g., Cl−) increases the electron diffusion rate in the film/solution interface, which makes the thermodynamically unstable α'‐Ti phase be preferentially corroded.

Recrystallization effect on surface passivation of Hastelloy X alloy fabricated by laser powder bed fusion

Post-heat treatment is generally adopted in the additive manufacturing field due to its alleviation of high residual stress and modification of rapid-solidified multilevel heterogeneous microstructure, and the related performance of the heat-treated counterparts calls for a systemic investigation to build a criterion of the heat treatment procedure. In this work, we focus on the heat treatment effects on the recrystallization of the Hastelloy X alloy produced by the laser powder bed fusion (LPBF) method, and the related surface passivation of the heat-treated counterparts is meticulously assessed as well. Results show that the multilevel heterostructure for LPBF Hastelloy X alloy consists of sub-micro dislocation cell substructures with Cr/Mo elemental segregation, fine columnar grains, and periodically-distributed molten pools. After heat treatment, partially and fully recrystallized structures for LPBF Hastelloy X alloys were achieved at 1100 and 1200 °C for 1 h, respectively. Furthermore, the as-built LPBF Hastelloy X alloy shows superior corrosion resistance while the heat-treated one (1100 °C) exhibits the worst in the borate buffer solution. The growth of passive film exhibited a highly linear correlation with the nucleation process controlled by diffusion, and high dislocation density and low angle grain boundary decreased the diffusion coefficient of cation vacancies, augmenting the nucleation sites of the passive film and enhancing its growth rate. Moreover, the micro-galvanic effect resulting from the partially recrystallized microstructure actively facilitated the formation of inhomogeneous porous passive films, leading to the worst corrosion resistance.

Effect of Annealing Temperature on Electrochemical Properties of Zr56Cu19Ni11Al9Nb5 in PBS Solution.

The electrochemical properties of as-cast Zr56Cu19Ni11Al9Nb5 metallic glass and samples annealed at different temperatures were investigated using potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) in phosphate buffer saline (PBS) solution. It was shown that passivation occurred for the as-cast sample and the samples annealed at 623-823 K, indicating good corrosion resistance. At higher annealing temperature, the corrosion resistance first increased, and then decreased. The sample annealed at 823 K exhibited the best corrosion resistance, with high spontaneous corrosion potential Ecorr at -0.045 VSCE, small corrosion current density icorr at 1.549 × 10-5 A·cm-2, high pitting potential Epit at 0.165 VSCE, the largest arc radius, and the largest sum of Rf and Rct at 5909 Ω·cm2. For the sample annealed at 923 K, passivation did not occur, with low Ecorr at -0.075 VSCE, large icorr at 1.879 × 10-5 A·cm-2, the smallest arc radius, and the smallest sum of Rf and Rct at 2173 Ω·cm2, which suggested the worst corrosion resistance. Proper annealing temperature led to improved corrosion resistance due to structural relaxation and better stability of the passivation film, however, if the annealing temperature was too high, the corrosion resistance deteriorated due to the chemical inhomogeneity between the crystals and the amorphous matrix. Optical microscopy and scanning electron microscopy (SEM) examinations indicated that localized corrosion occurred. Results of energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) illustrated that the main corrosion products were ZrO2, CuO, Cu2O, Ni(OH)2, Al2O3, and Nb2O5.

Influence of multiphase evolution on corrosion resistance of AlxCoCrFeNi alloys determined by transmission electron microscopy

The atomic structural evolution of the precipitated phase and the metastable pitting corrosion behavior of AlxCoCrFeNi alloys were investigated. With the increase of Al content, the (Cr, Fe)-rich phase in AlxCoCrFeNi alloys changed from FCC (A1 phase) to BCC (A2 phase) structure, and their shapes changed from strip to sphere, but the increase of the (Al, Ni)-rich phase (B2 phase) deteriorated their corrosion resistance. Al0.25CoCrFeNi alloy is single phase FCC structure, while Al0.75CoCrFeNi alloy is FCC + B2 structure, and Al1.0CoCrFeNi and Al1.5CoCrFeNi alloy are A2 + B2 structures. The Al1.5CoCrFeNi alloy had the worst corrosion resistance with the weak potential difference between the precipitated phases. Although the element segregation (nano-B2 phase) and the large potential difference at the interphase boundary were regarded as a factor of galvanic corrosion, the passive film played a key role in the corrosion resistance of AlxCoCrFeNi alloys.

Corrosion behavior and mechanism of X80 pipeline steel welded joints under high shear flow fields

The internal-pipeline local corrosion in the welded joint region has been a widely concerning issue, particularly under the synergistic effect of high shear stress and electrochemical corrosion, which can easily result in pipeline rupture. Classical electrochemical testing techniques and wire beam microelectrode (WBE) are used to investigate the local corrosion behavior of X80 steel welded joints in a CO2-saturated NACE solution at different flow rates (velocities of 3 m/s, 5 m/s and 7 m/s), and the corrosion product composition and characteristics are analyzed via scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and three-dimensional (3D) measuring laser microscopy. The results show that different welded joint zones exhibit different corrosion degrees. The heat-affected zone (HAZ) shows the worst corrosion resistance, whereas the base metal (BM) and weld metal (WM) show similar corrosion resistances. The HAZ is an anode that corrodes unsatisfactorily at high flow rates, and the enhanced wall shear stresses peel off part of the dense corrosion product film, promoting the development of local corrosion. Therefore, the HAZ zone is a weak link in the X80 steel welded joints. This study provides scientific guidelines for the corrosion protection of long-distance oil & gas pipelines.

Combined effects of irradiation and hydrogen on the mechanical and corrosion performances of the ferrite in duplex phase steels

Structural materials in nuclear reactor cores suffer from severe corrosion and weakened mechanical properties under the combined influences of hydrogen and irradiation. In this study, we studied the peak damaged region (PDR) in the ferrite phase of a duplex stainless steel post proton irradiation, which is featured with a relatively higher concentration of hydrogen and level of irradiation damages than that of the uniformly damaged region (UDR). It is found that the irradiation-induced hardening effect is more evident in UDR than in PDR, and the PDR exhibits a much larger drop of electron work function and worse corrosion resistance than the UDR. Moreover, the oxide film on the PDR shows a much lower electrical resistivity than that of the UDR. The degradation of mechanical performance and corrosion resistance is associated with the local enrichment of hydrogen and the formation of G-phase in the PDR under the unique combined influence of hydrogen and irradiation. This study sheds lights on the synergetic effects of hydrogen and irradiation on the degradation of steels in reactor cores.

Microstructure and corrosion behavior of bobbin tool friction stir welded 2219 aluminum alloy

This study employed the bobbin tool friction stir welding (BT-FSW) technique to weld 2219 aluminum alloy with 6 mm thickness. The microstructure investigation revealed that the weld nugget zone (WNZ) has a small number of coarse θ phases, whereas the heat-affected zone (HAZ) exhibits colossal amount of θ' phases. The impedance analysis demonstrated that the corrosion resistance of the WNZ is better than that of other zones. Also, the salt spray corrosion test showed that the WNZ has the best corrosion resistance, whereas the base metal (BM) has the worst corrosion resistance. Therefore, the poor corrosion resistance of the BM can be attributed to a high content of the precipitates.

Calcium-magnesium-alumina-silicate (CMAS) corrosion behavior of A6B2O17 (A=Zr, Hf; B=Nb, Ta) as potential candidate for thermal barrier coating (TBC)

Developing new systems with excellent properties is of great significance to the progress of TBC. We herein study the CMAS corrosion behavior of four A6B2O17 ceramics to evaluate the feasibility for TBC application. Zr6Nb2O17 has the worst corrosion resistance and Hf6Ta2O17 shows the best. The effects of elements A and B are reflected in the differences of corrosion products and reverse dissolution process, respectively. The dense corrosion layer containing CaTa2O6 and HfSiO4 is an important factor for Hf6Ta2O17 to prevent further corrosion. The present results highlight the merit of Hf6Ta2O17 as a promising candidate for CMAS-resisted TBC.