Electrochemical behavior of multicomponent amorphous and nanocrystalline Zr-based alloys in different environments

Electrochemical behavior of multicomponent melt spun Zr-based amorphous as well as nanocrystalline alloys have been studied in three different corrosive media (neutral NaCl, basic NaOH and acidic H₂SO₄ solutions). Due to the presence of strong passivating elements, (Zr and Ti) melt spun ternary alloys (Zr₅₅Ti₂₅Ni₂₀) have shown complete passivation in NaCl solution even as they contain a small amount of crystallinity. Amorphous multicomponent alloys containing Cu (Zr₅₈Cu₂₈Al₁₀Ti₄ and Zr₆₅Cu_7.5Al_7.5Ni₁₀Pd₁₀) show active nature in NaCl solution and this is strongly related to selective dissolution of base metal (Zr) and enrichment of Cu in the pit region. In NaOH and H₂SO₄ solutions, all the alloys have shown complete passivation irrespective of the alloy composition.     

Oxidation behavior of amorphous and nanoquasicrystalline Zr–Pd and Zr–Pt alloys

Oxidation behavior of amorphous and nanoquasicrystalline Zr₇₀Pd₃₀ and Zr₈₀Pt₂₀ alloys melt-spun at different wheel speeds has been studied in air by non-isothermal and isothermal techniques. Oxidation resistance of amorphous alloys has been found to be the lowest in comparison to the partially and fully crystallized Zr alloys. It has also been observed that oxidation does not induce crystallization of the amorphous phase. It has been shown that the oxygen diffusion rate increases gradually in the order of crystalline, nanoquasicrystalline, partially nanocrystalline and amorphous states of these alloys. Possible micromechanism of oxidation and the role of different grain/interface boundaries on the oxygen diffusion has been discussed.     

Corrosion behaviour of Ni-Zr-Ti-Si-Sn amorphous plasma spray coating

Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ amorphous material was deposited by a vacuum plasma spraying technique onto steel and copper substrates in order to investigate their behaviour in a corrosive environment. For comparison, the same alloy was prepared as amorphous ribbons by melt spinning. The amorphous nature of the coatings and ribbons was characterized by XRD, DSC and TEM, while XPS and AES analyses were performed to understand the origin of passivation and mode of corrosion. The corrosion behaviour of the coating was studied in H₂SO₄ and HCl solutions open to air at room temperature. Potentiodynamic polarisation and galvanic coupling tests were carried out on the substrate and the coating. It was found that the formation of Zr-, Ti- and Si-rich passive oxide layers provide a high corrosion resistance in H₂SO₄ solution while the breakdown of the passive layer by chloride ion adsorption was responsible for pitting corrosion of the Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ amorphous ribbons in HCl solution. Galvanic corrosion was the dominant corrosion mechanism for the coating/copper hybrid structure, in contrast to the Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ amorphous coating, which efficiently protected the steel substrate in the corrosive environment.     

Electrochemical response of AlNiLa amorphous and devitrified alloys

The electrochemical response of Al_94−xNi₆La_x 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.     

Electrochemical corrosion behaviors of straight WC–Co alloys: Exclusive variation in grain sizes and aggressive media

The electrochemical corrosion behaviors of straight WC–10Co cemented carbides with grain sizes of 1.2, 2.6, 6.1 and 8.2 μm, were comparatively investigated in the solutions of NaOH (pH = 13), Na₂SO₄ (pH = 7) and H₂SO₄ (pH = 1) respectively. To insure a sole variable of WC grain sizes, specific magnetic saturation values of the alloys are adjusted to be identical. The results show a good linear dependence for R_ct (charge transfer resistance) and I_corr (corrosion current density) against the grain sizes. A high sensitivity of the grain sizes to both R_ct and I_corr are identified in NaOH and H₂SO₄. In the solutions of NaOH and Na₂SO₄, the alloys with smaller WC grain sizes exhibit better corrosion resistances, while the alloys with larger WC grain sizes exhibit better corrosion resistances in H₂SO₄. Additionally, in terms of the corrosiveness, NaOH is the weakest and H₂SO₄ is the most aggressive for all the alloys. The corrosion mechanisms were discussed in light of the SEM surface observation, X-ray photoelectron spectroscope analysis and the electrical equivalent circuits for electrochemical impedance spectroscopy.     

The effect of molybdenum on the corrosion behaviour of the high-entropy alloys Co1.5CrFeNi1.5Ti0.5Mox in aqueous environments

The purpose of this study is to investigate the electrochemical properties of the Co_1.5CrFeNi_1.5Ti_0.5Mo_x 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 Co_1.5CrFeNi_1.5Ti_0.5Mo_x 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.     

Electrochemical properties and surface analysis of Cu–Zr–Ag–Al–Nb bulk metallic glasses

The electrochemical properties and surface characteristics of Cu–Zr–Ag–Al–Nb bulk metallic glasses (BMGs) were investigated. The alloys exhibit excellent corrosion resistance after immersion in 1N H₂SO₄ and 1N NaOH. The corrosion rates of the alloys in chloride-ion-containing solutions significantly decrease by alloying with Nb element. The formation of Zr- and Nb-enriched surface films could be responsible for the high corrosion resistance.     

Leaching of heavy metal elements in solder alloys

Leaching behavior of heavy metal elements from Sn–3.5Ag–0.5Cu, Sn–9Zn, and Sn–37Pb solder alloys and their joints was investigated in typical H₂SO₄, NaCl and NaOH solutions. The leaching amount of Sn from solder joints was more than that from solder alloys and the leaching amount of Sn from Sn–3.5Ag–0.5Cu solder joint in the NaCl solution was the most. The surface corrosion products on the solder and their joints were composed of oxide, oxide hydroxide or oxychloride of the component element. Much more surface oxides for the samples treated in the NaCl solution produced than that in the NaOH and H₂SO₄ solutions.     

Ni对Zr-Cu-Al系非晶合金在NaCl溶液中腐蚀性能的影响

利用动电位极化和电化学阻抗谱研究了Ni元素对Zr-Cu-Al系非晶合金在3.5wt.%NaCl中性溶液中的电化学腐蚀行为的影响规律。结果表明：含Ni元素的Zr₅₅Cu₃₀Ni₅Al₁₀比Zr₅₅Cu₃₅Al₁₀非晶合金在NaCl溶液中具有更优异的耐腐蚀性能。Zr-Cu-Al系非晶合金在NaCl溶液中发生点腐蚀,圆形腐蚀坑内布满泡沫状孔洞。通过腐蚀前后的元素分布对比,发现Zr-Cu-Al非晶合金在Cl^_-作用下合金元素选择性溶解。含Ni元素的非晶合金形成致密的钝化膜,抑制了金属元素的选择性溶解,从而提高了耐腐蚀性能。研究结果可为耐Cl^_-环境腐蚀非晶合金成分设计及其应用提供参考。     

Comparative studies on the corrosion properties of a Fe-Mn-Al-Si steel and an interstitial-free steel

Recent developments in a group of super ductile Fe-Mn-Al-Si steels with high-manganese content demands for more research in the corrosion behavior of such steels. The corrosion properties of the Fe-Mn-Al-Si steel was studied in acidic (0.1 M H₂SO₄), alkaline (0.1 M NaOH) and chloride-containing (3.5% NaCl) environments, using immersion and polarization experiments and compared with that of interstitial-free (IF) steel. In acidic solution, the Fe-Mn-Al-Si steel exhibited significantly lower corrosion resistance than that of IF steel. Though the Fe-Mn-Al-Si steel showed lower corrosion resistance as compared to IF steel in chloride solution, the difference was not as substantial as observed in acidic medium. However, in alkaline solution, the Fe-Mn-Al-Si steel showed no significant difference in the corrosion resistance in comparison with that of IF steel, and moreover exhibited substantially high corrosion resistance than in acidic and chloride solution. The post-corrosion characterization studies showed higher corrosion attack of the Fe-Mn-Al-Si steel exposed to acidic solution as compared to that in alkaline and chloride solutions, which is consistent with the corrosion measurement data.     

Corrosion property of copperized layer on Zr formed by double glow plasma surface alloying technique

Zr and its alloys have excellent mechanical properties as new structural material,but in specific application environment,its corrosion resistance still needs to be further explored.In this work,double glow plasma surface alloying technique was used for copperizing on pure Zr surface.Besides,X-ray diffraction(XRD),scanning electron microscope(SEM) and energy dispersion spectrum(EDS) were employed to characterize the samples.Furthermore,research was also conducted on the polarization curve of the samples in different solutions.Copperizing on surface can improve corrosion resistance of pure Zr in 3.5 % Na Cl and 0.5 moláL-1Na OH solutions.Especially in 0.5 moláL-1Na OH solution,the corrosion resistance can achieve significant improvement.However,copperizing has no influence on the improvement of corrosion resistance of pure Zr in 0.5 moláL-1H2SO4 solution.The results may provide new insight into way for improving the corrosion property of zirconium alloys.     

Corrosion behaviour of Fe80-xCoxB10Si10 metallic glasses in sulphate and chloride media

The corrosion behaviour of a series of glassy alloys, Fe_80-xCo_xB₁₀Si₁₀ (x = 0, 15, 30, 55, 70, 80), well known for their magnetic properties, has been investigated in sulphate- and chloride-containing solutions of different pH, employing weight loss measurements. In order to point out preferential dissolution reactions of metallic glasses constituent elements, analyses of the solutions were performed after corrosion tests by means of plasma source mass spectrometry and optical emission spectroscopy. A higher aggressivity of the sulphate containing solutions has been observed. The amorphous alloys exhibit an increased corrosion resistance with the increase of cobalt content. Increasing the pH of the aggressive media from 1.5 to 5.6 a decrease of two orders of magnitude in the corrosion rates has been observed. The corrosion products have been investigated by means of X-ray diffraction and scanning electron microscopy. Hydrated iron oxide Fe₂O₃ · H₂O was the major constituent of the film formed on iron-rich amorphous alloys immersed in sulphate-containing media.     

On the role of Ca in suppressing the corrosion of Pb anode in H2SO4

Abstract-The anodic behaviour of some Pb-Ca (0·2–0·8 per cent) alloys in H₂SO₄ solutions has been studied both under potentiostatic and galvanostatic conditions. It has been shown that the protective nature of the PbSO₄ film is markedly improved by alloying Ca with Pb. The role of Ca in increasing the corrosion resistance of Pb in H₂SO₄ is discussed.     

Effect of the aluminium content of AlxCrFe1.5MnNi0.5 high-entropy alloys on the corrosion behaviour in aqueous environments

High-entropy alloys (HEAs) are a newly developed family of multi-component alloys. The potentiodynamic polarization and electrochemical impedance spectroscopy of the Al_xCrFe_1.5MnNi_0.5 alloys, obtained in H₂SO₄ and NaCl solutions, clearly revealed that the corrosion resistance increases as the concentration of aluminium decreases. The Al_xCrFe_1.5MnNi_0.5 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.     

Electrochemical behavior of Ti-Mo alloys applied as biomaterial

Electrochemical investigation on the as-cast Ti-Mo alloys (4-20 Mo wt.%) applied as biomaterials in Na₂SO₄ and Ringer physiological solutions is reported. Analyses of the open-circuit potential indicated that all alloys present spontaneous passivation. SEM and cyclic voltammograms obtained in the Ringer solution showed that the samples studied do not present pitting corrosion at potentials up to 8 V (SCE), indicating high corrosion resistance. Open-circuit potential profiles of the anodic oxides growth in both solutions show that the presence of chloride ions during the anodization does not influence the oxides’ chemical stability, and also clearly indicate that adding Mo to pure Ti improves the stability of the anodic oxides. All these results suggest Ti-Mo alloys promissory to be applied as biomaterials.     

Corrosion behavior of nanocrystalline (Ni70Mo30)90B10 alloys in 0.8 M KOH solution

Nanocrystalline materials are claimed to exhibit improved properties as a result of their novel microstructure. The corrosion behavior of nanocrystalline (Ni₇₀Mo₃₀)₉₀B₁₀ alloys prepared by crystallization from the amorphous state was studied and compared with that of their amorphous and coarse-grained counterparts. Special emphasis was given to the relationship between microstructure and corrosion resistance. It was concluded that nanocrystalline (Ni₇₀Mo₃₀)₉₀B₁₀ alloys are less sensitive to corrosion in alkaline solutions than the coarse-grained material. This behavior was related to their small grain size and homogeneous single phase microstructure. They provide a uniform substrate where it is easy to form a passive film, consisting essentially of Ni(OH)₂ for the alloy studied.     

Corrosion behaviour of die-cast AZ91D magnesium alloy in aqueous sulphate solutions

The corrosion behaviour of die-cast AZ91D magnesium alloys in sulphate solutions was investigated by SEM, FTIR and polarization measurements. For immersion times less than 48 h, no pitting corrosion occurred and only generalized corrosion was apparent. According to the polarization curves, the corrosion rate order of the die-cast AZ91D Mg alloy in three aqueous solutions was: NaCl > MgSO₄ > Na₂SO₄. The main corrosion products were Mg(OH)₂ and MgAl₂(SO₄)₄·22H₂O in the sulphate solutions and the product film was compact. Precipitation of MgAl₂(SO₄)₄·22H₂O required a threshold immersion time.     

Cr元素对Fe基块体非晶合金形成能及腐蚀性能影响的研究

利用微合金化技术,制备了Fe_68.4-xCo_7.6Si₇B₁₀P₅C₂Cr_x (x=0, 1, 2, 3)非晶合金,并分别使用单辊急冷甩带法和铜模铸造法制备了带状和棒状样品。借助XRD、DSC、DTA表征该非晶合金系的热力学性能与非晶形成能;并进一步采用电化学动电位极化曲线法研究了该非晶合金系在硫酸溶液中的的耐腐蚀性能。实验结果表明,通过微量添加Cr元素的方法,使该合金系的非晶形成能普遍提高,当Cr元素添加量为2%时,获得了该系列非晶合金中的最大过冷液体区间(ΔTx=57K),并且成功制备了直径为5mm的圆棒状样品;同时,由于Cr元素的添加,在1N浓度的硫酸溶液中,材料表面上形成富含Cr元素的保护层,可以有效阻止材料内部的进一步腐蚀,耐腐蚀性能明显得到改善。     

Corrosion protection of magnesium alloys by cerium, zirconium and niobium-based conversion coatings

A new Ce, Zr and Nb-based conversion coating was designed for AZ91 and AM50 magnesium alloys. The corrosion protection provided by this coating was evaluated by electrochemical measurements (polarization curves, electrochemical impedance spectroscopy) in Na₂SO₄ electrolyte, and accelerated atmospheric corrosion tests (humid, SO₂ polluted air, and salt spray). Its chemical composition was characterized by X-ray photoelectron spectroscopy (XPS). Electrochemical measurements showed that Mg alloys treated during 24 h in the Ce-Zr-Nb conversion bath exhibit: (i) increased corrosion potential, (ii) decreased corrosion and anodic dissolution current densities, and (iii) increased polarization and charge transfer resistances. The accelerated corrosion tests revealed excellent atmospheric corrosion resistance for all Ce-Zr-Nb-treated samples, with or without an additional layer of epoxy-polyamide resin lacquer or paint. XPS analysis showed that the coating includes CeO₂, Ce₂O₃, ZrO₂, Nb₂O₅, MgO, and MgF₂ as main components. No significant modification of the chemical composition was observed after cathodic and anodic polarization in Na₂SO₄. This new coating provides improved corrosion resistance, and excellent paint adhesion. It offers an alternative to the chromate conversion coating for magnesium alloys.     

Inhibiting effects of butyl triphenyl phosphonium bromide on corrosion of mild steel in 0.5 M sulphuric acid solution and its adsorption characteristics

Butyl triphenyl phosphonium bromide (BuTPPB) has been evaluated as a corrosion inhibitor for mild steel in 0.5 M H₂SO₄ solutions using galvanostatic polarisation and potentiostatic polarisation measurements. The study was also complemented by infra red (IR) spectroscopy, scanning electron microscopy (SEM) and quantum chemical calculations. Galvanostatic polarisation measurements showed that the presence of BuTPPB in aerated 0.5 M H₂SO₄ solutions decreases corrosion currents to a great extent and the corrosion rate decreases with increasing inhibitor concentration at a constant temperature. At 298K, inhibition efficiency was found to be 94.5% for 10⁻⁷ M BuTPPB which increased to about 99% for the BuTPPB concentration of 10⁻² M. The effect of temperature on the corrosion behaviour of mild steel was studied at five different temperatures ranging from 298 to 338K. The polarisation curves clearly indicate that BuTPPB acts as a mixed type inhibitor. Adsorption of BuTPPB on the mild steel surface follows the Langmuir isotherm.Potentiostatic polarisation measurements showed that passivation was observed only for lower BuTPPB concentrations (10⁻⁵ and 10⁻⁷ mol l⁻¹) for the mild steel in 0.5 M H₂SO₄. IR and SEM investigations also confirmed the adsorption of BuTPPB on the mild steel surface in 0.5 M H₂SO₄ solutions. The molecular parameters obtained using PM3 semi-empirical method, were correlated with the experimentally measured inhibitor efficiencies.