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1.
A. Roy 《Corrosion Science》2007,49(6):2486-2496
The electrochemical response of Al94−xNi6Lax alloys (x = 4, 5, 6, 7) after different stages of devitrification was studied in 0.05 M Na2SO4 as well as in different concentrations [0.001 M, 0.01 M and 0.1 M] NaCl solutions. Complementary crystallization studies were carried out to elucidate the composition dependent phase evolution in these alloys. It was observed that the primary crystallization did not cause any deterioration in the corrosion resistance of the alloys as compared to the amorphous alloys. In the case of Al87Ni6La7, there was actually an improvement in the passivating ability in benign media. The various primary crystalline phases in the different alloys investigated did not cause different electrochemical responses. However, the onset of secondary crystallization caused a reduction in the corrosion resistance in the NaCl media through a loss in passivating ability of all the alloys. This is due to increased galvanic activity as well as the loss of the amorphous phase. 相似文献
2.
Electrochemical behaviour of Ni-base alloys exposed under oil/gas field environments 总被引:1,自引:0,他引:1
The electrochemical behaviour of Ni-base alloys (Inconel 625, Inconel 718, G3 and Incoloy 825) is carried out at 80 °C in CO2/H2S corrosion environments using cyclic potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. The passivity mechanisms are analysed and discussed. In addition, some significant characterisation parameters such as Ecorr, Ipass, Epit, Epp, ΔE and Ipass in cyclic polarisation curves are analysed and compared to reveal the corrosion resistance of various Ni-base alloys. The equivalent circuit model and ZsimpWin software are utilised to discuss the Nyquist plots of various Ni-base alloys. The diffusion mechanism in EIS measurement is discussed. The result shows that the corrosion resistance of the Ni-base alloys to CO2 corrosion or CO2/H2S corrosion follows the sequence: Inconel 625 > G3 > Inconel 718 > Incoloy 825. H2S works as a cathodic depolariser with accelerating initiation of the corrosion process. 相似文献
3.
The EIS technique was used to analyze the electrochemical reaction behavior of Alloy AZ91 in H3PO4/KOH buffered K2SO4 solution at pH 7. The corrosion resistance of Alloy AZ91 was directly related with the stability of Al2O3 · xH2O rich part of the composite oxide/hydroxide layer on the alloy surface. The break down of the oxide layer was estimated to occur mainly on the matrix solid solution phase in Alloy AZ91. The mf capacitive loop arose from the relaxation of mass transport in the solid oxide phase in the presence of Al2O3 · xH2O rich part and from Mg+ ion concentration within the broken area in the absence of Al2O3 · xH2O rich part in the composite oxide structure on the alloy surface. The lf inductive loop had tendency of disappear when the dissolution rate of the alloy decreased as a result of the formation of the protective oxide layer. 相似文献
4.
Fe1−xMgx alloy films (with x ? 43.4 at.% Mg) were deposited by dc magnetron sputtering onto glass slide substrates. The objective of this study was to characterise the corrosion properties of these alloys in saline solution for application as new friendly environmentally sacrificial coatings in the protection of steel structures. The morphological and structural properties of the alloys were systematically studied prior to electrochemical experiments, and then the degraded surfaces were analysed to determine the composition and nature of corrosion products. Alloys with <25 at.% Mg were single-phase body-centred cubic (bcc) with enlarged lattice parameters, whereas for magnesium contents above 25 at.%, amorphisation occurred. The reactivity of the alloys in saline solution is strongly dependent on the Mg content and the alloy structure. The incorporation of magnesium leads to an open circuit potential shift of the alloy towards more negative values, that confers an attractive interest of these alloys as sacrificial coatings. A transition in corrosion activity is observed at 25 at.% Mg from which the reactivity decreases with the magnesium content increase. The evolution of the alloy corrosion behaviour is discussed in terms of structural and corrosion products evolution versus magnesium content. 相似文献
5.
J.G. Gonzalez-Rodriguez E. Mejia V.M. Salinas-Bravo A. Martinez-Villafañe 《Corrosion Science》2009,51(8):1619-1627
A study of the effect of lithium content (1, 3 and 5 wt.%) and heat treatment (400 °C during 144 h) on the corrosion behavior of Ni3Al alloy has been carried out in a 62 mol.%Li2CO3-38 mol.%K2CO3 mixture at 650 °C using electrochemical techniques. Employed electrochemical techniques included potentiodynamic polarization curves, linear polarization resistance, LPR, electrochemical impedance spectroscopy, EIS, and electrochemical noise, measurements EN. Results have shown that the alloys exhibited an active-passive behavior regardless of the heat treatment. For alloys without heat treatment, the most corrosion resistant was the Ni3Al base alloy, but when they were heat treated, the most corrosion resistant was the alloy containing 3%Li. EIS results showed that for short immersion tests, the corrosion process was under diffusion control, but for longer exposure times, the presence of a protective scale was evident. All the alloys were highly susceptible to a localized type of corrosion according to EN measurements and supported by SEM micrographs. 相似文献
6.
On the corrosion of binary magnesium-rare earth alloys 总被引:1,自引:0,他引:1
The corrosion properties of high-pressure die cast (HPDC) magnesium-rare earth (RE) based alloys have been studied. Binary additions of La, Ce and Nd to commercially pure Mg were made up to a nominal 6 wt.%. It was found that the intermetallic phases formed in the eutectic were Mg12La, Mg12Ce and Mg3Nd, respectively. Results indicated that increasing RE alloying additions systematically increased corrosion rates. This was also described in the context of the electrochemical response of Mg-RE intermetallics - which were independently assessed by the electrochemical microcapillary technique.This study is a discrete effort towards revealing the electrochemical effect of carefully controlled binary alloying additions to magnesium in order to elucidate the microstructure-corrosion relationship more generally for HPDC Mg alloys. Such fundamental information is seen to not only be useful in understanding the corrosion of alloys which presently contain RE additions, but may be exploited in the design of magnesium alloys with more predictable corrosion behaviour. There is a special need to understand this relationship - particularly for magnesium that commonly displays poor corrosion resistance. 相似文献
7.
The corrosion of three Fe-xCr alloys (x = 8, 12, 18 wt.%) was examined at 600 °C in reducing atmospheres containing HCl and H2S with two different H2S contents and compared with the behavior of the same materials in H2S-free H2-CO2 and H2-HCl-CO2 mixtures producing similar oxygen and chlorine pressures. Exposure to the low-H2S gas mixture had only a reduced effect on the behavior of Fe-8Cr and Fe-18Cr, but increased significantly the corrosion rate of Fe-12Cr. Increasing the H2S level accelerated the corrosion of all the alloys, but particularly that of Fe-18Cr. In both cases only minor amounts of sulfur and chlorine were present close to the alloy/scale interface. An increase of the Cr content reduced the corrosion rate in both H2S gas mixtures, especially in the range 8-12 wt.% Cr, due to a larger volume fraction of Cr2O3 in the scale. The results have been discussed on the basis of the thermodynamic stability diagrams of the Fe-O-Cl-S and Cr-O-Cl-S systems. 相似文献
8.
Electrochemical techniques were used to characterize the corrosion behavior of four new binary alloys xSn-Ag (x = 26, 50, 70 and 96.5 wt%) alloys and their individual metal components in nitric acid solutions. The experimental data were collected by using open-circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Over the concentration range studied (0.075-4.5 M), each of the two corrosion parameters (Ecorr and icorr) shows a regular dependency on both the alloy composition and the solution concentration. In general, for all studied samples, especially pure Ag and those with lower Sn contents (26 and 50 wt%), increasing the acid concentration increases icorr, meanwhile causes a shift of the corresponding Ecorr towards more positive values. This is probably due to the increase in the effect of cathodic depolarizer as the nitric acid concentration is increased. EIS results at the free corrosion potential confirmed well this behavior, where at concentrations ?1.5 M the thickness of the surface film increases while its resistance decreases with increasing tin wt%, indicating formation of less protective thicker film. However, at higher concentrations all samples exhibit identical behavior. 相似文献
9.
The relation between corrosion resistance and microstructure of Mg-Zn-Y alloys with a long period stacking ordered (LPSO) phase has been investigated. In order to clarify the influence of microstructure evolution by rapid solidification on the occurrence of localized corrosion such as filiform corrosion, several Mg97.25Zn0.75Y2 (at. %) alloys with different cooling rates were fabricated by the gravity casting, copper mould injection casting and melt-spinning techniques and their corrosion behavior and microstructures were examined by the salt immersion tests, electrochemical measurements, XRD and TEM. When the cooling rate was less than 3 × 104 K s−1, filiform corrosion propagated in the early stage of salt immersion test, due to formation of a massive block-shaped LPSO phase during casting. On the other hand, when the cooling rate was increased up to 3 × 104 K s−1, rapidly solidified (RS) alloys exhibited excellent corrosion resistance because of grain refinement and formation of a supersaturated single-phase solid solution. Large-sized Mg97.25Zn0.75Y2 alloys fabricated by consolidation of the RS ribbons also exhibited excellent corrosion resistance with passivity. Enhancement of microstructural and electrochemical homogeneities in the Mg-Zn-Y alloys by rapid solidification techniques results in the passivity of substrate materials. 相似文献
10.
Electrochemical passive properties of AlxCoCrFeNi (x = 0, 0.25, 0.50, 1.00) alloys in sulfuric acids
This study investigates the electrochemical passive properties of AlxCoCrFeNi alloys in H2SO4 by potentiodynamic polarization, EIS, and weight loss tests from 20 to 65 °C. Experimental results indicate that Al harms the corrosion resistance in H2SO4 at temperatures exceeding 27 °C owing to the porous and inferior nature of the protection oxide film of Al in these alloys. Closely examining the Arrhenius plots of corrosion current density reveals that both pre-exponential factor A and activation energy Ea increase with Al content. However, A affects corrosion current density more significantly than Ea at higher temperatures and, conversely, at lower temperatures. 相似文献
11.
The purpose of this study is to investigate the electrochemical properties of the Co1.5CrFeNi1.5Ti0.5Mox high-entropy alloys in three aqueous environments which simulate acidic, marine, and basic environments at ambient temperature (∼25 °C). The potentiodynamic polarisation curves of the Co1.5CrFeNi1.5Ti0.5Mox alloys, obtained in aqueous solutions of H2SO4 and NaOH, clearly revealed that the corrosion resistance of the Mo-free alloy was superior to that of the Mo-containing alloys. On the other hand, the lack of hysteresis in cyclic polarisation tests and SEM micrographs confirmed that the Mo-containing alloys are not susceptible to pitting corrosion in NaCl solution. 相似文献
12.
High-entropy alloys (HEAs) are a newly developed family of multi-component alloys. The potentiodynamic polarization and electrochemical impedance spectroscopy of the AlxCrFe1.5MnNi0.5 alloys, obtained in H2SO4 and NaCl solutions, clearly revealed that the corrosion resistance increases as the concentration of aluminium decreases. The AlxCrFe1.5MnNi0.5 alloys exhibited a wide passive region, which extended >1000 mV in acidic environments. The Nyquist plots of the Al-containing alloys had two capacitive loops, which represented the electrical double layer and the adsorptive layer. SEM micrographs revealed that the general and pitting corrosion susceptibility of the HEAs increased as the amount of aluminium in the alloy increased. 相似文献
13.
An exploratory study of the corrosion of Mg alloys during interrupted salt spray testing 总被引:3,自引:0,他引:3
A first systematic investigation was carried out to understand the corrosion of common Mg alloys (Pure Mg, AZ31, AZ91, AM30, AM60, ZE41) exposed to interrupted salt spray. The corrosion rates were also evaluated for these alloys immersed in 3 wt.% NaCl by measuring hydrogen evolution and an attempt was made to estimate the corrosion rate using Tafel extrapolation of the cathodic branch of the polarisation curve. The corrosion of these alloys immersed in the 3 wt.% NaCl solution was controlled by the following factors: (i) the composition of the alpha-Mg matrix, (ii) the volume fraction of second phase and (iii) the electrochemical properties of the second phase. The Mg(OH)2 surface film on Mg alloys is probably formed by a precipitation reaction when the Mg2+ ion concentration at the corroding surface exceeds the solubility limit. Improvements are suggested to the interrupted salt spray testing; the ideal test cycle would be a salt spray of duration X min followed by a drying period of (120-X) min. Appropriate apparatus changes are suggested to achieve 20% RH rapidly within several minutes after the end of the salt spray and to maintain the RH at this level during the non-spray part of the cycle. The electrochemical measurements of the corrosion rate, based on the “corrosion current” at the free corrosion potential, did not agree with direct measurements evaluated from the evolved hydrogen, in agreement with other observations for Mg. 相似文献
14.
《Intermetallics》2015
Fe-based soft-magnetic metallic glasses (MGs) of Fe80−xCrxP9C9B2 (x = 0, 2, 5, 8 and 16 at.%) with high glass-forming ability (GFA), good soft-magnetic properties and high corrosion resistance are fabricated. With the addition of Cr to FePC-based alloys, the GFA and saturation magnetization (Ms) slightly decrease while the corrosion resistance effectively increases. The Fe–Cr–P–C–B BMGs exhibit good GFA and fully glassy rods can be produced up to 1.8 and 1.5 mm in diameter for the 2 and 5 at.% Cr added alloys, respectively. The alloys with 2 and 5 at.% Cr addition also show good soft-magnetic properties featured by high Ms of 1.16 and 1.04 T, low coercivity of 2.7 and 2.2 A/m, respectively. Besides, the corrosion behavior of the alloys was studied by immersion tests and potentiodynamic polarization measurements. It was found that the addition of Cr efficiently enhances the corrosion resistance of Fe–Cr–P–C–B alloys and the glassy alloy with 5 at.% Cr addition exhibits better corrosion resistance in comparison with the stainless steel SUS304 in 3 mass% NaCl solution. The combination of large GFA, good soft-magnetic properties, high corrosion resistance as well as low cost makes the Fe–Cr–P–C–B alloys as promising soft-magnetic and anti-corrosive materials for industrial applications. 相似文献
15.
The corrosion resistance of three indigenous nitric acid grade (NAG) type 304L stainless steel (SS), designated as 304L1, 304L2 and 304L3 and two commercial NAG SS designated as Uranus-16 similar to 304L composition and Uranus-65 similar to type 310L SS were carried out in nitric acid media. Electrochemical measurements and surface film analysis were performed to evaluate the corrosion resistance and passive film property in 6 N and 11.5 N HNO3 media. The results in 6 N HNO3 show that the indigenous NAG 304L SS and Uranus-65 alloy exhibited similar and higher corrosion resistance with lower passive current density compared to Uranus-16 alloy. In higher concentration of 11.5 N HNO3, transpassive potential of all the NAG SS shows a similar range, except for Uranus-16 alloy. Optical micrographs of all the NAG SS revealed changes in microstructure after polarization in 6 N and 11.5 N HNO3 with corrosion attacks at the grain boundaries. Frequency response of the AC impedance of all the NAG SS showed a single semicircle arc. Higher polarization resistance (RP) and lower capacitance value (CPE-T) revealing higher film stability for indigenous NAG type 304L SS and Uranus-65 alloy. Uranus-16 alloy exhibited the lowest RP value in both the nitric acid concentration. Auger electron spectroscopy (AES) study in 6 N and 11.5 N HNO3 revealed that the passive films were mainly composed of Cr2O3 and Fe2O3 for all the alloys. The corrosion resistance of different NAG SS to HNO3 corrosion and its relation to compositional variations of the NAG alloys are discussed in this paper. 相似文献
16.
The corrosion inhibition behavior of benzotriazole, Na3PO4 and their mixture on carbon steel in 20 wt.% (0.628 mol l−1) tetra-n-butylammonium bromide aerated aqueous solution was investigated by weight-loss test, potentiodynamic polarization measurement, electrochemical impedance spectroscopy and scanning electron microscope/energy dispersive X-ray techniques. The inhibition action of BTA or SP or inhibitors mixture on the corrosion of carbon steel is mainly due to the inhibition of anodic process of corrosion. The results revealed that inhibitors mixtures have shown synergistic effects at lower concentration of inhibitors. At 2 g l−1 BTA and 2 g l−1 SP showed optimum enhanced inhibition compared with their individual effects. 相似文献
17.
Early stages of the evolution of Al2O3 scales formed on a FeCrAlRE alloy (Kanthal AF) have been investigated by analytical TEM. The samples were oxidized isothermally at 900 °C in dry O2 or O2 + 40% H2O for 1 h or 24 h. All oxide scales exhibited a two-layered structure, with a continuous inward growing α-Al2O3 inner layer and an outward growing outer layer. After 1 h, the outer oxide layer consisted of γ-Al2O3 in both environments. After 24 h exposure in dry O2, the γ-Al2O3 in the outer oxide layer was partly transformed to α-Al2O3 and spinel oxide (Mg1−xFexAl2O4). In contrast, the γ-Al2O3 in the outer layer was not transformed after 24 h in O2 + 40% H2O, showing that water vapour stabilizes γ-Al2O3. All oxide scales contained a Cr-rich band, a product of the initial oxidation. The inner α-Al2O3 layer is suggested to nucleate on Cr2O3 or Cr2−xFexO3 in the initial oxide. 相似文献
18.
Corrosion of Mg-Y alloys was studied using electrochemical evaluations, immersion tests and direct observations. There were two important effects. In 0.1 M NaCl, the corrosion rate increased with increasing Y content due to increasing amounts of the Y-containing intermetallic. In 0.1 M Na2SO4, the corrosion rate decreased with increasing Y content above 3%, attributed to a more protective surface film, despite the intermetallic. The corrosion rate evaluated by electrochemical impedance spectroscopy was somewhat smaller than that evaluated from H evolution as expected from the Mg corrosion mechanism. A mechanism is proposed for filiform corrosion. Direct in situ corrosion observations revealed that a predominant feature was hydrogen evolution from particular parts of the alloy surface. 相似文献
19.
Yuming Xiong 《Corrosion Science》2008,50(1):15-22
In the present paper, the corrosion behavior of Ti60 alloys with an aluminide, TiAlCr, and enamel coatings in moist air containing NaCl vapor at 700-800 °C were studied. The results showed that the TiAlCr and aluminide coatings failed to protect the substrate from corrosion due to the cyclic formation of volatile products during corrosion at 800 °C. However, an uneven continuous protective Al2O3 scale could form on the aluminide coating during corrosion at 700 °C. And the enamel coating could protect Ti60 from corrosion due to its high thermochemical stability and matched thermal expansion coefficient with substrates of Ti-base alloys during corrosion. 相似文献
20.
《Intermetallics》2014
Sintered Nd–Fe–B magnets with and without Dy2O3 were prepared by powder blending method. The temperature-dependent magnetic properties, thermal stability, microstructure and corrosion resistance of sintered magnets were investigated. The temperature-dependent magnetic properties revealed that with intergranular addition of Dy2O3, the reversible temperature coefficients β and α in the range of 293–373 K were both lowered, indicating that the thermal stability was effectively improved. This was also verified by the decreased irreversible flux loss (hirr) and the increased maximum operating temperature (MOT). Moreover, the electrochemical and accelerated corrosion results clearly evidenced that the corrosion resistance of Nd–Fe–B magnet was also modified by addition of Dy2O3. Furthermore, the related mechanisms on improved thermal stability and corrosion resistance were systematically discussed. 相似文献