High Corrosion Susceptibility Research Articles

Enhancing corrosion and tribology performance of stainless steel with DLC coatings: Effects of doping and multilayered structures

The increasing demand for energy production has expanded oil and gas extraction, particularly in harsh exploration sites with highly corrosive media. In the Brazil's pre-salt layer, rich in oil reserves, high NaCl content and CO2 presence may induce sweet corrosion. Corrosion resistant alloys are often used for better performance, and among them, austenitic stainless steels (SS) offer good balance of cost and properties. However, pre-salt acidic and salty environment may induce localized corrosion, making protective coatings a viable option to prolong the lifespan of components exposed to these environments. Diamond-like carbon (DLC) coatings are a great alternative, as besides being chemically stable, they improve mechanical properties of the coated material, such as higher hardness and wear resistance and lower friction coefficient. Therefore, the performance of different types of DLC on the anti-corrosion protection of SS was evaluated. Four DLC types were tested: a hydrogenated amorphous DLC; a multilayered film (DLC-M); and films with fluorine (DLC-F) and silicon (DLC-S). The films showed chemical and structural differences, evidenced by Raman, SEM/EDS and XPS analysis. Their tribological performances were evaluated through scuffing resistance tests; the base DLC showed the highest resistance, followed by DLC-F and DLC-M. DLC-S films didn't exhibit satisfactory tribological performance. For corrosion characterization, potentiodynamic polarization tests were conducted in NaCl and CO2-saturated NaCl solutions. In the NaCl tests, DLC films exhibited impressive anti-corrosion properties, with DLC-F delivering the highest performance, followed by DLC-M, DLC-S, and base DLC. 316 L SS showed high corrosion susceptibility in the CO2-saturated solution, but the coatings also improved corrosion resistance in this setting. The DLC, DLC-S and DLC-M showed similar Ecorr and jcorr values, while DLC-F demonstrated superior corrosion resistance with higher Ecorr and lower jcorr values.

Unexpectedly high corrosion susceptibility near fusion boundaries of Inconel 625 manufactured by laser powder bed fusion

The intergranular corrosion (IGC) resistance of Inconel 625 produced by laser powder bed fusion was investigated according to ASTM-G28 method A. Unexpected severe corrosion near fusion boundaries was found. The initiation and expansion of corrosion along fusion boundaries and the relationship between microstructure and corrosion behavior were analyzed. This unusual corrosion behavior was related to the Volta potential variation near fusion boundaries. This Volta potential difference was caused by the Al2O3 nanoparticles and Mo, Nb-rich precipitates near the fusion boundaries. This finding may enhance the understanding of corrosion behavior of LPBFed nickel alloys.

Preparation of corrosion‐resistant composite coating on AZ91D magnesium alloy through hydrothermal method

AbstractThe high corrosion susceptibility of magnesium alloy has become a practical problem which restricts its wide application in many fields. To improve its surface properties, a composite coating has been successfully prepared on the surface of AZ91D magnesium alloy using a one‐step hydrothermal method. The coating surface possesses a dense structure in the form of scales and has an adhesion strength of 3B. The effect of different preparation conditions on the coating thickness and corrosion resistance is discussed. The coating heated at 180°C for 2 h showed the best corrosion resistance in a 3.5 wt% sodium chloride solution, with a reduction in corrosion current density of 5 orders of magnitude compared to the bare sample. This solution significantly improved the corrosion resistance of the magnesium alloy and helped to further realize the application of magnesium alloys in corrosive environments.

Galvanic corrosion of AA5052/304SS welded joint with Zn-based filler metal in marine engineering

Galvanic corrosion and localized corrosion behavior of AA5052/weld seam/304SS tri-metallic couples were examined by EIS, ZRE, SKP and SVET tests after tungsten inert gas (TIG) arc welding. The results showed that the weld seam had a relatively high corrosion susceptibility. The asymmetric corrosion of weld seam was attributed to the macro-galvanic effect between the weld seam/AA and the weld seam/SS. Localized corrosion of Zn in δ-FeZn10 induced the corrosion trenches and channels initiation. The deep corrosion propagation at the weld seam/SS interface was brought on by local acidity and micro-galvanic effect.

Characterization and evaluation of stable localized corrosion in a 7075-T6 aluminum alloy FSW joint before and after anodizing treatment

The microstructure and corrosion processes of a friction stir welded (FSW) 7075-T6 aluminum alloy joint, before and after anodizing surface treatment, have been characterized by advanced techniques, and the feasibility of anodizing treatment as a corrosion mitigation method has been evaluated. The results showed that different zones of the FSW joint had distinctly different microstructure and consequently different corrosion behavior in NaCl solution. Stable localized corrosion occurred in the transitional regions between the thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ), and was characterized by intergranular corrosion. The intergranular corrosion was ascribed to the galvanic coupling effect between Cu-rich grain boundary precipitates and the precipitates free zones (PFZs). Although anodizing and the subsequent sealing treatments could greatly improve the corrosion resistance of the base metal, the TMAZ/HAZ transition regions still showed much higher corrosion susceptibility than other regions. The high corrosion susceptibility of the FSW joint after anodizing treatment is not ascribed to the difference of the anodic oxide film in the regions, but the heterogeneous microstructure of the alloy beneath the anodic film. The present paper has shown that the stable localized corrosion in the FSW joint is intrinsically stemmed from the welding process itself and traditional mitigation method such as anodizing treatment cannot solve the problem; more effective corrosion mitigation methods are still awaited.

A novel corrosion transformation process in aluminum alloy / galvanized steel welded joint

Replacing steel with aluminum alloy is appealing to realize the lightweight of metal structures. Novelis AC 170 PX aluminum alloy and ST06 Z galvanized steel sheets were lap welded by gas tungsten arc welding (GTAW) with ER4047 filler wire and the corrosion behavior of the joint was characterized. The results revealed that the zinc-rich zone had the highest corrosion susceptibility. The difference of localized corrosion between the adjacent area near the rod-shaped and the layered Fe4Al13 phases was explained by galvanic effect. When Zn in the zinc-rich zone was exhausted, the corrosion process of the joint was controlled by the second phases and corrosion products.

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

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.

Effect of inhomogeneous microstructure evolution on the mechanical properties and corrosion behavior of rotary friction welded AA2024 joints

The intrinsic flaws of radial gradient heat generation and uneven deformation during rotary friction welding process will damage the structural integrity of the resultant joint but almost no attention has been paid before. The relationship between radial inhomogeneous microstructure, mechanical properties and corrosion behavior of rotary friction welded 2024 aluminum alloy joint was thus systematically investigated to reveal the impact. The results showed that the highest and lowest tensile strength appeared in 0.25R and 0.75R positions along radius, respectively. And the texture evolution in 0.25R and 0.75R positions can be summarized as: Copper {112}<111> → S{123}<634> → Brass {011}<211>(strong) → Brass {011}<211> (weak), Copper {112}<111> → S{123}<634> → Rotated Goss {110}<110> → Brass {011}<211> (weak), respectively. The corrosion resistance of rotary friction welded joint is gradually weakened along radius, caused by the different distribution of grain size, second phase particles and residual stress. The heat affected zone (HAZ), thermo-mechanically affected zone (TMAZ) adjacent to HAZ and dynamic recrystallization zone (DRZ) exhibited high corrosion susceptibility and occurred severe exfoliation corrosion. But the TMAZ adjacent to DRZ and base metal acquired the good corrosion resistance due to the dispersive distribution of GPB zones. Furthermore, the qualitative relationship between microhardness and corrosion susceptibility was revealed. The regions with low microhardness exhibited high corrosion susceptibility while the regions with high microhardness (except DRZ) presented good corrosion resistance. • Microstructure and mechanical properties of joints unevenly distributed along radius. • Texture evolution in 0.25R and 0.75R position was systematically investigated. • The corrosion resistance in TMAZ adjacent to DRZ is the highest. • Qualitative relation between microhardness and corrosion susceptibility was revealed.

Influence of aging treatment on the microstructure, mechanical properties and corrosion behavior of spray deposited Al-Mg-Li-Sc-Zr alloy

Correlation among microstructural, strengthen mechanism, corrosion resistance, and aging treatment of a lightweight Al-5.45Mg-1.86Li-0.38Sc-0.12Zr alloy fabricated by spray deposition and hot extrusion were investigated. The results revealed that Al3Li and S1 (Al2MgLi) were the main precipitated phases in the alloy after solution and aging treatments. The increase of aging time from 12 h to 20 h at 120 °C significantly improved the alloy strength due to the fine and homogeneously dispersed Al3Li precipitates. With further prolonging the aging time from 20 h to 35 h, dislocation bypasses the Al3Li precipitates by the Orowan mechanism, and the S1 phases located at the grain boundaries undermine the continuity of the grain boundary. This led to a decrease in the mechanical properties and corrosion resistant of the alloy. The high corrosion susceptibility from prolonging the aging time is caused by the coarsening of S1 precipitates.

Effect of Homogenization Temperature and Soaking Time on the Microstructure and Corrosion Properties of a Twin Roll Casted AA3003

The AA3003 alloy is widely used as fin material in heat exchangers. The lifetime of these heat exchangers is mostly determined by their corrosion properties. Twin roll casting (TRC) of AA3003 material is known to often result in the formation of a macrosegregation area of alloying elements toward the center plane of the casted strip (center line segregation = CLS). Considering the potential exposure of cross-sectional areas of TRC material in the heat exchanger fin application, and the relatively high corrosion susceptibility of the CLS, the study of this region is of key importance to understand the microstructural effects on the resulting corrosion mechanisms and kinetics for these materials. Typically the alloys are homogenized to bring the microstructures closer to an equilibrium state, but the impact of this heat treatment on the corrosion properties is insufficiently studied. Therefore, this study investigates the effect of different homogenization procedures on the corrosion properties of the CLS and the interaction of the intermetallic particles with the surrounding aluminum matrix. This work shows that the pitting corrosion resistance is greatly dependent on the homogenization temperature, with better corrosion resistance obtained with higher temperature, especially near the CLS. This difference in corrosion behavior is completely attributed to a difference in microstructure and not to an oxide layer effect. Furthermore, it is observed that not only temperature will have a large influence on the corrosion resistance, but duration of the heat treatment as well.

Fabrication of low-cost Ni-P composite coating on Mg alloys with a significant improvement of corrosion resistance: Critical role of mitigating the galvanic contact between the substrate and the coating

High galvanic corrosion susceptibility and expensive Pd-activation process are two critical obstacles for the application of electroless nickel (EN) plating on Mg alloy. In this work, the plasma electrolytic oxidation (PEO) coating was sealed by chemical conversion post-treatment to obtain an intermediate layer with high electrical resistance, aiming to minimize the susceptibility of galvanic corrosion. A low-cost Ag-activation technique was proposed to catalyze the EN plating process. Results indicate a dramatic improvement of corrosion resistance of EN composite coating. In addition, the composite coating also exhibits high adhesion, hardness, electrical conductivity and low magnetism.

Corrosion Behavior of High-Mn Austenitic Fe-Mn-Al-Cr-C Steels in NaCl and NaOH Solutions.

The corrosion behavior of austenitic Fe–Mn–Al–Cr–C twinning-induced plasticity (TWIP) and microband-induced plasticity (MBIP) steels with different alloying elements ranging from 22.6–30 wt.% Mn, 5.2–8.5 wt.% Al, 3.1–5.1 wt.% Cr, to 0.68–1.0 wt.% C was studied in 3.5 wt.% NaCl (pH 7) and 10 wt.% NaOH (pH 14) solutions. The results obtained using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques, alongside optical microscopy analysis, revealed pitting as the dominant corrosion mechanism in high-Mn TWIP steels. An X-ray diffraction analysis of the surface revealed that the main corrosion products were hematite (Fe2O3), braunite (Mn2O3), and hausmannite (Mn3O4), and binary oxide spinels were also identified, such as galaxite (MnAl2O4) and jacobsite (MnFe2O4). This is due to the higher dissolution rate of Fe and Mn, which present a more active redox potential. In addition, a protective Al2O3 passive film was also revealed, showing enhanced corrosion protection. The highest corrosion susceptibility in both electrolytes was exhibited by the MBIP steel (30 wt.% Mn). Pitting corrosion was observed in both chloride and alkaline solutions.

Insight into the corrosion behaviour and degradation mechanism of pure zinc in simulated body fluid

Zn is considered as a promising degradable biomaterial. However, concerns exist for its application as the degradation mechanism of pure Zn in physiological solutions is still not clear. Results indicated that the corrosion product film showed a laminated structure with complex layers, which were ZnO/Zn(OH)2, a Ca/P phase, zinc compounds, and a Ca/P phase from the inside out, respectively. The localized corrosion initiated at grain boundaries and expanded towards the interior of grains with higher corrosion susceptibility, or advanced towards the depth. Additionally, the nature of the corrosion product film and localized corrosion synergistically determined the degradation rate.

Deposition of anti-corrosion hybrid film of hexamethylene diaminetetrakis (methylene phosphonic acid)/hydroxyapatite on biodegradable Mg: Influence of deposition procedures

Magnesium and its alloys are promising biodegradable materials because of their light weight and superior mechanical properties. However, the high corrosion susceptibility of magnesium is the main obstacle that hinders the application of Mg in biomedical applications. In this article, two approaches have been employed to fabricate hybrid films of hexamethylene diamine tetrakis (methylene phosphonic acid) (HMDTMPA) and hydroxyapatite (HA) on Mg. The direct dipping method involves an immersion in a single solution containing both calcium, phosphate, and the organic compound. However, it results in poor-quality loose films, due to unstable film of monocalcium phosphate monohydrate (MCPM). The other method involves immersion in two separated solutions: Ca-P solution and HMDTMPA solution. Our results showed that the corrosion resistance was enhanced about 12-times compared with HMDTMPA film due to the formation of a stable hybrid film of dicalcium phosphate dihydrate (DCPD). The mechanism of formation of anti-corrosion DCPD was discussed on the light of SEM, EDS, FTIR, XRD and XPS.

Effects of quenching agents, two-step aging and microalloying on tensile properties and stress corrosion cracking of Al-Zn-Mg-Cu alloys

In this paper, the tensile properties and stress corrosion resistance of two Al-Zn-Mg-Cu alloys were tested by tensile test and slow stress rate tensile test. The microstructures of the precipitation were observed by transmission electron microscopy, and the proportion and size of the precipitates were measured by ImageJ software. This work revealed that Sc and Zr microalloying will instead reduce the SCC resistance of Al-Zn-Mg-Cu alloys and increase the strength reduction of Al-Zn-Mg-Cu alloys, under certain heat treatment. The area fraction of GBP can be effectively adjusted by the combine of changing quenching agents, step-aging and minor additive of Sc and Zr. With the increase of area fraction of precipitates at the grain boundary, the slow stress corrosion susceptibility decreased first and then increased. This is because when the area fraction exceeds 22.3%, the low stress cracking mechanism will change from hydrogen embrittlement mechanism to anodic dissolution mechanism. The combination of heat treatment and Sc, Zr microalloying enable the area fraction reach approximately 22.3 %, which will make the Al-Zn-Mg-Cu alloys have high strength and low slow stress corrosion susceptibility.

Corrosion and wear protection of mild steel substrates by innovative PVD coatings

Today, innovative coatings must ensure wear protection and corrosion resistance for engineering materials with high corrosion susceptibility, e.g. mild steels, as well as the current sustainability criteria in terms of environment protection and health.PVD technology fulfils most of these demands, but unfortunately, the corrosion protection performance is unsatisfactory due to the typically low coating thicknesses of only few micrometres.One solution to overcome the corrosion problem are TiMgREN (RE = Rare Earth) based coatings, which were developed by the authors. Even with 5 μm thick monolithic TiMgGdN coatings a corrosion resistance of at least 800 h could be achieved in the salt spray test without any macroscopic corrosion attack.In the present work, the influence of the coating composition, the substrate material and the surface roughness on the corrosion properties was examined. Besides, the application of Gd as alloying element, the influence and the effect of other rare earth metals (La, Ce) on the corrosion performance were investigated.As benchmark, the TiMgGdN coatings were compared with industrial standard PVD coatings, DLC and electroplated Cr regarding the corrosion and the wear performance.The coatings were characterized concerning their microstructural, mechanical and chemical properties. Salt spray tests as well as electrochemical measurements were carried out to examine the corrosion properties of the coated specimens. Furthermore, ball on disk wear tests were conducted by reciprocal dry sling tests by using a SRV 3 tribometer.It was shown that by variation of the deposition parameters, the coating properties could be improved concerning both, corrosion and wear performance. Furthermore, the effect of the used rare earth metal type and the rare earth metal content on the coating properties was investigated. The TiMgGdN coatings exhibit superior corrosion properties in comparison to the industrial standard coatings.

Enhanced Electrochemical and Tribological Properties of AZ91D Magnesium Alloy via Cold Spraying of Aluminum Alloy

Magnesium (Mg) alloys have remarkable physical and mechanical properties for various aerospace applications. However, the high corrosion susceptibility and low wear resistance of Mg alloys restrict their wider use. To overcome these problems, 6061 Al alloy coatings were fabricated via the cold spraying process on the AZ91D Mg alloy substrate and a detailed comparative study on the wear and corrosion properties was carried out. The microstructure analysis of the compact coatings revealed low porosity with no phase change during the deposition process. The coatings showed improved corrosion resistance up to seven times as confirmed by potentiodynamic polarization and electrochemical impedance spectroscopy measurements in 3.5 wt.% NaCl aqueous solution. The as-deposited coatings were also compared with commercial bulk alloys of similar composition for their suitability to industrial applications. The tribological behavior of the coatings and substrate was investigated using tribometer. The wear resistance of the coatings improved more than two orders of magnitude as compared to the substrate. Abrasive and oxidative wear mechanisms were dominant in the coatings and substrate. The results showed that cold spraying of 6061 Al alloy on AZ91D Mg alloy could be an auspicious process to overcome the poor corrosion and wear resistance of this Mg alloy for practical industrial applications.

Corrosion behaviour of laser powder bed fused bulk pure magnesium in hank’s solution

Laser powder bed fusion (LPBF) can be used to additively manufacture magnesium(Mg)-based biodegradable materials. However, the influence of the processing parameters on the microstructure and consequent corrosion behaviour of bulk pure Mg fabricated by LPBF needs to be investigated. Electrochemical measurements and mass loss tests were carried out to evaluate the corrosion resistance of Mg components manufactured by LPBF. It was found that the laser-introduced defects initiated localised corrosion and lowered the overall corrosion resistance. Loosely fused Mg materials had high corrosion susceptibility. Hence, the processing parameters should be carefully selected to obtain favourable corrosion resistance of Mg manufactured by LPBF.

Effect of thermal aging on oxide film of stainless steel weld overlay cladding exposed to high temperature water

Characteristics of the oxide film formed on stainless steel weld overlay cladding aged at 400 °C for different times in high temperature water were studied. The results showed that thermal aging showed no obvious effect on the volume fraction of ferrite phase but resulted in high corrosion susceptibility of the aged ferrite phase mainly. The oxide film formed on the unaged cladding material consisted of 100-nm-thick inner oxide layer (FeCr2O4 and Cr2O3) and Fe-rich outer oxide particles (Fe3O4) with a size of <500 nm. By comparison, 300-nm-thick Fe-Cr inner oxide layer (FeCr2O4, Cr2O3 and Fe3O4) and outer oxide particles (Fe3O4 and FeCr2O4) with a size of <700 nm formed on the aged ferrite phase. Spinodal decomposition was considered as the main factor to promote the corrosion of the aged ferrite phase, and existence of carbides along phase boundary facilitated corrosion of the cladding material in high temperature water.

Corrosion in Tap Water and Hot Water Supply Facilities of Stainless Steel Type 304 Pipes

We performed corrosion case study and corrosion tests to assess the corrosion resistance of stainless steel type 304 pipes in tap water and hot water facilities. Circulating test equipment used for corrosion tests and two types of sample, plates and straight pipe specimens, were examined under different conditions of residual chlorine concentration in the test water. The results of case study analysis indicated that high degrees of pitting corrosion occurred on straight pipes with inner diameter < 50 mm. The results of corrosion tests showed that the residual chlorine concentration around the pitting corrosion of stainless steel type 304 was greater than 0.3 mg/L in the plate, regardless of the remaining chlorine concentration in the straight pipe specimens. These results suggest that straight pipes have higher corrosion susceptibility because of bending during production.