Deterioration Of Corrosion Resistance Research Articles

Effects of Fe addition on the mechanical and corrosive properties of biomedical Co-Cr-W-Ni alloys for balloon-expandable stents

Co-20Cr-15W-10Ni (mass%, CCWN) alloy is extensively used as a platform material for balloon-expandable stents. In this study, the mechanical properties of CCWN alloy are improved following the addition of Fe, and the effects of Fe addition on the mechanical and corrosive properties of the alloy are investigated. As-cast specimens were fabricated by adding pure Fe to a commercially available CCWN alloy (base alloy) such that the resulting alloys contained 4, 6, and 8 mass% Fe. The as-cast specimens were subjected to homogenization heat treatment at 1523 K for 7.2 ks and then hot-forged at 1473 K (as-forged specimens). The as-forged specimens were cold-rolled at a reduction rate of 30% and heat-treated at 1473 K for 300 s (recrystallized specimens). The matrix of the recrystallized base- and Fe-containing alloys consisted of a single γ (face-centered cubic)-phase. The Fe-added alloys revealed precipitates composed of the η-phase (M6X-M12X-type phase, M: metallic element, X: C and/or N). The average grain size of the recrystallized base and Fe-added alloy specimens was approximately 34 μm and the amount of added Fe had no significant effect on the static recrystallization behavior of the resulting alloys. Alloys containing 6 mass% or more Fe showed improvements in strength and ductility compared with the base alloy. When the Fe-added alloys were compared, their strength decreased whereas their ductility increased when the added Fe increased. Because Fe acts as a γ-phase-stabilizing element for Co, Fe addition increases the stacking fault energy of the base alloy, resulting in the formation of the ε (hexagonal close-packed)-phase owing to the suppression of strain-induced martensitic transformation (SIMT), and improvements in ductility. No deterioration in corrosion resistance was observed following the addition of up to 8 mass% Fe to the base alloy. Based on these results, the addition of Fe to CCWN alloy may be considered an effective method to improve its mechanical properties, especially ductility, without impairing its corrosion resistance. The results of this study will be useful for the future development of Ni-free Co-Cr alloys for next-generation, small-diameter stents.

Formation of heterogeneous microstructure and its effect on corrosion properties of high-silicon stainless steel S38815 weldment

This study aims to clarify the formation of heterogeneous microstructure and its effect on corrosion properties of high-silicon stainless steel (high-Si SS) S38815 weldment. A series of tests about microstructure and electrochemical characteristics were performed, including the electron backscatter diffraction (EBSD) analysis, Mott-Schottky tests, electrochemical impedance spectroscopy (EIS) tests, potentiodynamic and potentiostatic polarization tests. The formation mechanism of heterogeneous microstructure related to high-silicon and its correlation on corrosion was discussed extensively. The results show that the significantly deformed and recrystallised grains were observed at the low temperature heat affected zone (LT-HAZ) and high temperature heat affected zone (HT-HAZ) respectively. The metastable pitting and low impedance values were formed in the above region, despite their low donor density. The deterioration in corrosion resistance of S38815 weldment as a result of high-angle grain boundaries (HAGBs) and carbides is more pronounced than the beneficial impact of Cr and Si oxidation. This study provides valuable references to the manufacturing and enhancing the anti-corrosion properties of this high-Si SS.

Room Temperature Corrosion Behavior of Selective Laser Melting (SLM)-Processed Ni-Fe Superalloy (Inconel 718) in 3.5% NaCl Solution at Different pH Conditions: Role of Microstructures

Inconel 718 (UNS N07718) is a nickel-base superalloy containing iron that is used at cryogenic temperatures (arctic pipe components) and at high temperatures (gas turbines). This alloy is also used in off-shore oil drilling due to its high overall strength and resistance to corrosion. Inconel 718 components are created by a selective laser melting (SLM) additive manufacturing route and result in isotropic fine-grained microstructures with metastable phases (such as Laves phases) that are not usually present in conventional manufacturing processes. In this work, SLM Inconel 718 alloy specimens were investigated in four different conditions: (1) As-manufactured (AS-AM), (2) Additively manufactured and hot isostatically pressed (AM-HIP), (3) As-manufactured and heat-treated (solution annealing followed by two-step aging), and 4) AM-HIP and heat-treated. Localized corrosion behavior was evaluated at room temperature in a 3.5% NaCl solution at three different pH conditions (pH 1.25, 6.25, and 12.25). Electrochemical tests, including linear polarization, cyclic polarization, potentiostatic conditioning, electrochemical impedance spectroscopy, and Mott–Schottky analyses, were used to compare the corrosion behaviors of the SLM specimens with that of the conventionally wrought IN718 samples. The results showed that the additively manufactured specimens showed better corrosion resistance than the wrought material in the acidic chloride solution, and the AM-HIP specimens exhibited superior corrosion resistance to the as-manufactured ones. Hot isostatic pressing resulted in the visible elimination of the dendritic structure, indicating compositional homogeneity as well as a significant decrease in porosity. In addition, the deleterious secondary phases, such as Laves and δ phases, were not observed in the microstructure of the HIPed samples. The AM-HIP material showed the highest corrosion resistance in all the pH conditions. The two-step aging treatment, in general, resulted in the deterioration of corrosion resistance, which could be attributed to the formation of γ′ and γ″ precipitates that increased the cathodic reaction catalytic activities. In the additively manufactured samples, the presence of the Laves phase was more detrimental to corrosion resistance than any other phases and MC carbide and grain boundary δ phase increased the susceptibility to corrosion in wrought materials.

Electrochemical behavior and passive film properties of Ce-added AlCoCrFeNi2.1 eutectic high-entropy alloys in sulfuric acid solution

Eutectic high-entropy alloys (EHEAs), represented by AlCoCrFeNi2.1, are considered to be promising materials. However, the study of the corrosion behavior of EHEAs remains limited, which hinders further development. This study investigated the effect of Ce addition on the electrochemical behavior and passive film properties of AlCoCrFeNi2.1 EHEAs in H2SO4 solutions. The results show that the addition of Ce changed the properties of the passive film formed on the alloys, resulting in reduction in the proportion of Cr2O3, and thereby reduced the corrosion resistance. Moreover, a higher Ce content in the EHEAs was found to correspond to a more pronounced deterioration in corrosion resistance. Compared with the film formed at 0.2 Vvs SCE, the film formed at 0.5 Vvs SCE exhibited more optimal physicochemical properties, leading to a decrease in the passive current density. Notably, Ce was absent in the film formed at 0.2 Vvs SCE, but present at 0.5 Vvs SCE.

On the evolution of protective oxide chemistry and corrosion resistance of electrodeposited FeCrMnNiCo-carbon nanotube composite coatings

ABSTRACT Reinforcement of carbon nanotube (CNT) into FeCrMnNiCo High Entropy Alloys (HEA) was carried out using electrodeposition method. Different volume fractions of functionalised CNTs (0.5, 1.0, 5.0, 10.0, 20.0, 30.0 mg/L) were dispersed in the aqueous electrolyte bath to synthesise HEA-CNT composite coatings. Effect of CNT addition on the phase constitution, morphology, composition, roughness, contact angle and ultimately on corrosion resistance of the pristine coating was investigated. The study revealed that the corrosion behaviour of the composite coatings was highly sensitive to the volume fraction of CNTs in the coatings. The change in the corrosion rate was, however, not monotonic and it was observed that the corrosion rate decreased progressively with CNT addition reaching a minimum followed by a sharp increase in corrosion rate thereafter. The protection efficiency of pristine coating was enhanced remarkably by 74.27% with the addition of an optimum amount (10 mg/L) of CNTs. The enhanced corrosion resistance was due to fine-grained morphology, reduced surface roughness from 1194. 9 ± 3.6 nm for pristine coating to 721.3 ± 1.8 nm for the highest corrosionresistant coating, enhanced hydrophobicity with a tremendous increase in water contact angle from 85.2° to 152.8°. Additionally, the dominance of more stable oxides of chromium (Cr2O3) and nickel (NiO) on the passive oxide layer made the coating less susceptible to corrosive media. Beyond the optimum CNT volume fraction, the drastic deterioration in corrosion-resistance observed beyond the optimum was attributed to increased surface defects in the forms of cracks due to the incorporation of agglomerated CNTs into the coating matrix.

Effect of TiC precipitation on the corrosion behavior of Monel K500 alloy in 3.5 wt.% NaCl solution

The microstructure of Monel K500 alloy was investigated consisting of (Ni-Cu-Al) solid solution matrix distributed with TiC precipitates. The semi-coherent interface was formed between the precipitates and the matrix, which reduced the phase boundary energy, resulting in the preferential corrosion of matrix instead of the interface in 3.5 wt.% NaCl solution. Immersion experiment combined with electrochemical test exhibited the uniform corrosion behavior of the alloy, covered with passivation film consisted of surface polycrystal layer and inner amorphous layer. Moreover, the accumulation of CuO in the film with time, led to generation of microcracks as well as deterioration of corrosion resistance.

Influence of Post Heat Treatment Condition on Corrosion Behavior of 18Ni300 Maraging Steel Manufactured by Laser Powder Bed Fusion.

Laser powder bed fusion (LPBF) is a promising additive-manufacturing process for metallic materials. It has the advantage of flexibility in product design, such that various mechanical parts can be fabricated. However, because metal parts are built-up in a layer-by-layer manner, the material fabricated by LPBF has an anisotropic microstructure, which is important for the design of materials. In this study, the corrosion resistance of 18Ni300 maraging steel (MS) fabricated by LPBF was explored considering the building direction. Furthermore, the effects of heat treatment and aging on the microstructure and corrosion resistance were investigated. Sub-grain cells formed by rapid cooling in LPBF improve the corrosion resistance of MS. As a result, the as-built MS has the highest corrosion resistance. However, the sub-grain cells are eliminated by heat treatment or aging, which causes the deterioration of corrosion resistance. In the case of 18Ni300 MS, the cylindrical sub-grain cells are formed and aligned along the heat dissipation direction, which is similar to the building direction; thus, a significant anisotropy in corrosion resistance is found in the as-built MS. However, such anisotropy in corrosion resistance is diminished by heat treatment and aging, which eliminates the sub-grain cells.

Effect of Reprocessing on Microstructure and Corrosion Resistance of Zr-Sn-Nb Alloy

To study the effect of reprocessing on the microstructure and corrosion resistance of Zr-Sn-Nb alloy, the original plates of Zr-Sn-Nb alloy were hot-rolled, cold-rolled and recrystallized to obtain the reprocessed plates. The microstructure of both plates was observed with a scanning electron microscope (SEM), a transmission electron microscope (TEM) and electron backscattering diffraction (EBSD). The original plates and reprocessed plates were put into a static autoclave for 300 days in 360 °C/18.6 MPa water. The relationship between the microstructure and corrosion resistance of the Zr-Sn-Nb alloy was discussed. The coarse deformation grains with twins and fine recrystallized grains were obtained, and grain sizes became smaller. The Ostwald ripening of second phase particles (SPPs) happened, and the average size of SPPs increased. Some SPPs changed from an HCP structure to an FCC structure. Reprocessing made the transition advance, which is related to the accelerated evolution of cracks in the oxide film and the increase in metal-oxide film interface roughness. The deterioration of corrosion resistance is closely related to the change of grain size, SPP size and SPP structure.

Development of a Thermomechanical Treatment Mode for Stainless-Steel Rings.

This article describes a technology for the thermomechanical treatment of stainless-steel piston rings. This technology makes it possible to obtain rings with an optimal combination of plastic and strength properties that is essential for piston rings. The following thermomechanical treatment is suggested for piston rings manufacturing: quenching at 1050 °C, holding for 30 min and cooling in water, then straining by the HPT method for eight cycles at cryogenic temperature and annealing at a temperature up to 600 °C. The resulting microstructure consisted of fine austenite grains sized 0.3 μm and evenly distributed carbide particles. Annealing above this temperature led to the formation of ferrite in the structure; however, preserving the maximum fraction of austenitic component is very important, since the reduction of austenite in the structure will cause a deterioration of corrosion resistance. The strength properties of steel after such treatment increased by almost two times compared with the initial ones: microhardness increased from 980 MPa to 2425 MPa, relative elongation increased by 20%. The proposed technology will improve the strength and performance characteristics of piston rings, as well as increase their service life, which will lead to significant savings in the cost of repair, replacement and downtime.

Electrochemical corrosion behavior of Ti‐3Mo alloy under different accelerated corrosion tests

AbstractThe electrochemical corrosion behavior of Ti‐3Mo alloys under different accelerated corrosion tests including seawater corrosion, soil corrosion, and stray current corrosion was investigated. Results showed that the icorr value gradually increased with the increase of NaCl/Na2SO4 concentration, indicating a worsening corrosion resistance of Ti‐3Mo alloy. The presence of stray current seriously destroyed the oxide film on the sample surface, and inhibited the regeneration of oxide film, thereby resulting in the deterioration of corrosion resistance. Besides this, the potential difference between duplex phases was prone to form a microgalvanic coupling, which promoted the dissolution of local regions.

Properties of SrCe0.95M0.05O3 (M = La, Pr, Y, Sn) thermal barrier materials

The lightly doped strontium cerates SrCe0.95M0.05O3, where М = Pr, Y, La, and Sn, are shown to maintain an invariable Pnma structure at heating in the air up to 1773 K. The decrease in the size of the doping atoms is found to be beneficial for tuning up the thermal expansion coefficient, reducing the average grain size and sinterability of ceramic samples. The doping with large atoms is accompanied by a deterioration in corrosion resistance in the melt of CMAS because of the formation of aluminates and silicates. The tin–doped derivative is not sufficiently stable because of the leaching of tin from the structure. The penetration of the CMAS melt into surface cracks and pores facilitates exfoliation of flakes from the surface, thus contributing to the degradation of cerite ceramics. The combination of small grain size and porosity, optimized thermal expansion, chemical robustness in the melts of CMAS, and high hardness distinguishes SrCe0.95Y0.05O3 as a promising thermal barrier coating material.

Intergranular precipitation-enhanced wetting and phase transformation in an Al0.4CoCrFeNi high-entropy alloy exposed to lead-bismuth eutectic

After exposure to oxygen-poor (10−13–10−14 wt%) liquid lead-bismuth eutectic (LBE) at 500 °C for 500 h, LBE penetrates more than one order of magnitude deeper in an FCC Al0.4CoCrFeNi high-entropy alloy (HEA) decorated with a network of BCC (Ni, Al)-rich intergranular (IG) precipitates than in a single-phase, FCC Al0.3CoCrFeNi HEA without the IG precipitate network. This deterioration of corrosion resistance is attributed to the energetic nature of the BCC/FCC interphase boundaries (IBs) and resultant IB wetting. The LBE ingress film selectively leaches nickel located at those low-indexed crystalline planes, resulting in phase transformation from FCC to BCC structure.

Evaluation of the Possibility of Using 1.4462 and 1.4501 Steel as a Construction Material for Apparatus Operating at an Increased Temperature and with Corrosive Factors.

The objective of this study was to determine the requirements for steels used as construction materials for chemical apparatus operating at an elevated temperature and to correlate them with the properties of the tested steels. The experimental part examined the influence of the annealing process on the structure and properties of X2CrNiMoN22-5-3 (1.4462) and X2CrNiMoCuWN25-7-4 (1.4501) steel. Heat treatment was carried out on the tested samples at a temperature of 600 °C and 800 °C. Changes were observed after the indicated time intervals of 250 and 500 h. In order to determine the differences between the initial state and after individual annealing stages, metallographic specimens were performed, the structure was analyzed using an optical microscope and the micro-hardness was measured using the Vickers method. Potentiostatic tests of the samples were carried out to assess the influence of thermal process parameters on the electrochemical properties of the passive layer. An increase in the hardness of the samples was observed with increasing temperature and annealing time, the disappearance of magnetic properties for both samples after annealing at the temperature of 800 °C, as well as a significant deterioration in corrosion resistance in the case of treatment at a higher temperature.

Study on Wettability and Corrosion Behavior of Al2O3 Doped Polyurea Coatings

The Al2O3 powder was added as a filler to polyurea and the effect of doping amount on Shore hardness and wetting property were investigated. The electrochemical impedance spectroscopy (EIS) was used to investigate the corrosion resistance of coating/aluminum alloy system in 0.1 mol/L NaOH solution. The results showed that with the increase of the doping amount, the Shore hardness of the coating increased and the contact angle on the aluminum alloy matrix decreased. By analyzing the results of the characteristics of EIS and the fitting results, doped Al2O3 powder can improve the coating corrosion resistance, but it may affect the density of the coating and reduce the impedance modulus during the initial stage of immersion. The relationship between the doping amount of Al2O3 powder and the corrosion resistance in this test was 5 wt % > 10 wt % > 15 wt % > 0 wt %. In general, in the doping range of this test, since the powder was uniformly distributed in the polyurea coating, the cohesive force of the polyurea can be lowered to cause an increase in the wetting property. At the same time, excessive dopped Al2O3 powder may deteriorate the compactness of the polyurea and the binding property of the polyurea itself may decrease, resulting in deterioration of corrosion resistance. However, the proper doping of Al2O3 powder in polyurea improves its overall performance.

Corrosion resistance of amorphous carbon film in 3.5 wt% NaCl solution for marine application

In this work, we fabricated the tetrahedral amorphous carbon (ta-C) films with thicknesses of 20 nm, 40 nm and hydrogenated diamond-like carbon (DLC:H) film with thickness of 1.1 μm on 316 stainless steel substrate (316SS). The electrochemical corrosion performances of two typical amorphous carbon (a-C) films in 3.5 wt% NaCl solution were focused. Results revealed that both ultrathin ta-C films exhibited superior corrosion resistance than that of DLC:H film, because the high content of sp3 bonded carbon and low porosity in ta-C films significantly suppressed the diffusion of corrosion media. However, a thickness threshold beyond 20 nm was proposed to obtain the superior corrosion resistance for ta-C films due to the emerged pitting of 316SS. For DLC:H film, the deterioration of corrosion resistance could be attributed to the hydrogen-containing interface, the large sp2 clusters with high electron transport, and the higher porosity density in carbon matrix.

Effect of synovial fluid temperature on the corrosion resistance of Ti6Al4V, Ti6Al7Nb, and CoCrMo alloys

AbstractThe frictional heat generated during the operation of the joint prosthesis in vivo could change the corrosion resistance of the prosthesis material. In this paper, the corrosion behavior of three medical alloys at different synovial fluid temperatures was analyzed using electrochemical measurement technology. Furthermore, the scanning electron microscope and energy‐dispersive spectrometer were used to characterize the surface morphology and composition of the alloys after long‐term immersion. The results show that increasing temperature causes the open‐circuit potential of titanium alloy to shift negatively and the corrosion tendency to increase. The increasing temperature leads to the decrease of activation energy of titanium alloy, which in turn results in the increase of corrosion current density and accelerated corrosion. The results of Nyquist curves confirmed that the radius of the capacitive arc decreased with the increase of temperature, indicating the deterioration of corrosion resistance. The CoCrMo alloy shows the same regularity as the titanium alloy in 0.9% NaCl, though no obvious regularity in 25% newborn bovine serum; this may be related to the complexity of the corrosion system.

Overview of cold gas dynamic dusting: problems and prospects

Problem. At present, the method of cold gas-dynamic coating for application of protective and restorative coatings is widely used in aerospace, automotive and other industries. Along with the excellent operational properties of the equipment for the method of CS there are also disadvantages: low coefficient of material use, possible porosity, which leads to a decrease in strength and deterioration of corrosion resistance. To eliminate the aforementioned shortcomings, high-pressure equipment is used to ensure the specified properties of surfaces and expand the application of the method of cold gas-dynamic spraying, at the same time, the costs of equipment and associated costs are multiplied by several levels. Goal. The analysis of the current state of the problem in the field of low pressure cold gasdynamic spraying (CS) on the possibility of influencing the quantitative and qualitative indices of the protective and restorative coatings created by this method and the study of the properties of such coatings was conducted in order to gain experience for further research in this field. Methodology. An analysis of literary sources led to the conclusion that it is necessary to revise the principle of modeling and development of equipment for producing coatings by the method of cold gas-dynamic spraying.. Results. The analysis of the current state of the issue in the field of influence on the quantitative and qualitative indicators of the protective and restorative coatings created by this method and the study of the properties of such coatings obtained by the method of CS showed that a more profound study of the influence on the temperature-speed parameters of particles of the spray material by gas-dynamic and external forces is required.Originality. The increasing demand for low-energy, environmentally safe, efficient and lowcost coating processes stimulates the search for and development of new alternative methods, one of which is cold spraying. Practical value. A third-party effect on the particle speed of the sprayed powder will not only reduce the temperature effect and, as a result, possible negative effects, but also significantly reduce the energy and material costs of the process, due to the rejection of expensive high-pressure equipment, as well as increase the efficiency of the process when working with low pressure.

Relation Between Zn Additions, Microstructure and Corrosion Behavior of New Wrought Mg-5Al Alloys

In the present study, the effect of varying Zn additions (0.93–3.16 wt%) on the corrosion resistance of wrought Mg-5Al alloys was studied and related to the microstructure changes. Three secondary phases were found: Al–Mn, β-Mg17Al12 enriched with Zn, and Φ-Mg21(Al, Zn)17; the latter observed only in alloys with relatively high Zn content. The corrosion behavior in short periods of immersion is related to pitting corrosion, and strongly influenced by micro-galvanic effects between the secondary phase particles and the α-Mg matrix. In long periods of immersion, a protective layer is formed, and filiform corrosion observed for alloys with Zn content above 1 wt%. However, the micro-galvanic effects still play a crucial role in deterioration of corrosion resistance in alloys with relatively high Zn content. These effects depend on the cathodic behavior of the particles, and on the total number of the particles presented on the alloy’s surface.

The influence of Mg addition and hydrostatic extrusion HE on the repassivation ability of pure Al, AlMg1 and AlMg3 model alloys in 3.5 wt-% NaCl

ABSTRACTCommercially pure aluminium and two model aluminium–magnesium alloys were subjected to hydrostatic extrusion (HE). The microstructure of materials was observed using optical microscopy (OM). All materials were subjected to electrochemical corrosion tests in the 3.5 wt-% water solution of sodium chloride. The potentiodynamic polarisation measurements and electrochemical impedance spectroscopy were performed after samples’ immersion in open circuit potential. The surface of samples after corrosion examination was observed with the use of scanning electron microscopy. It was stated that all undeformed materials underwent pitting corrosion and further pits repassivation, while after HE pitting was also observed, but pit repassivation did not occur. This may be related to the microstructural changes caused by deformation, such as grain refinement. What is more, the pits character changed with the addition of a different amount of Mg to Al. Deterioration of corrosion resistance was also observed for all materials after HE.

Microstructure, corrosion behavior, and surface mechanical properties of Fe oxide coatings on biomedical ZK60 Mg alloy

The Mg‐5.5Zn‐0.6Zr (in wt%, ZK60) alloy has been surface modified by dual Fe&O ion implantation and deposition (II&D) under different O2 fluxes from 0 to 40 sccm. The microstructure is investigated by glancing angle X‐ray diffraction, atomic force microscope, and scanning electron microscopy. The results show that the modified layers, with a gradient microstructure of outer deposition region and inner implantation region, are composed of α‐Fe + Fe&Mg mixture, FeO/Fe‐rich oxide + Fe&Mg mixture, and α‐Fe2O3/Fe‐rich oxide + Fe&Mg mixture for 0, 10, and 40 sccm O2 fluxes, respectively. The electrochemical and immersion tests in 37°C Hank's solution indicate an improvement in corrosion behavior under 0 and 10 sccm O2 fluxes, but a deterioration in corrosion resistance under 40 sccm O2 flux. In addition, the nanoindentation tests suggest that the dual Fe&O II&D simultaneously enhances the surface hardness and elastic modulus due to the formation of Fe and its oxide coatings.