Comparison of Nb- and Ta-effectiveness for improvement of the cyclic oxidation resistance of TiAl-based intermetallics

High-temperature cyclic oxidation resistance of Ti–45.2Al–7.2Nb and Ti–44.8Al–6.6Ta (in at.%) alloys is studied. The alloys were oxidized at 800–1000 °C for up to 380 h and oxidation kinetics was expressed as a function of weight gain versus time. Both as-cast and oxidized alloys were examined by optical and scanning electron microscopy, energy- and wave-dispersion spectrometry, X-ray diffraction and X-ray fluorescence spectrometry. In contrast to previously reported studies, tantalum is found to retard oxidation more effectively than niobium, despite its lower content in the investigated alloy. It also shows a significantly better adherence of oxide scales to the substrate, i.e. a lower tendency to scale spallation, particularly at 1000 °C. Chemical and phase analysis of oxidized alloys reveals considerable differences in element and phase distribution in oxidation-affected zones: 1. Niobium is observed to increase alumina amount in scales more effectively than tantalum. 2. Concentration of tantalum in scales is lower than of niobium. 3. Tantalum causes the occurrence of nitrides both in scales and in metallic substrate, while niobium supports formation of nitrides only in metallic substrate beneath scales. Differences between the investigated alloys are discussed in relation to oxidation mechanism, stability of Ta- and Nb-containing compounds.     

Corrosion resistance of Mg-Mn-Ce magnesium alloy modified by polymer plating

Polymeric nano-film on the surface of Mg-Mn-Ce magnesium alloy was fabricated by polymer plating of 6-dihexylamino-1,3,5-triazine-2,4-dithiol monosodium(DHN) to improve its corrosion resistance.The electrochemical reaction process was analyzed by cyclic voltammetry and two obvious peaks of oxidation reaction were observed.The static contact angle of distilled water on polymer-plated surface can be up to 106.3°while on the blank surface it is 45.8°.Potentiodynamic polarization results show that the polyme...     

Ta等离子体渗氮的非平衡热力学

讨论了Ta表面等离子体渗氨的热力学问题，将超平衡氢和非平衡热力学的反应耦合理论引入离子渗氮反应的计算，从理论上解释了等离子体和氢在Ta表面渗氮过程中的作用，给出了渗氮条件下的Na-N-O非平衡定态相图，与实验验结果符合得较好，实验表明，氢和等离子体的存在，有利于提高氮原子的活度，促进热力学上不稳定的Ta的氮化物的形成，抑制粗糙的Ta的氧化物的形成。     

Effect of Si nanoparticles on the corrosion protection performance of organic coating on carbon steel in chloride environment

This work examines the effect of silicon (Si) nanoparticles on the corrosion protection performance of epoxy coating over carbon steel by Electrochemical Impedance Spectroscopy (EIS) and Transmission Electron Microscopy. The EIS was performed in a 0.1 M NaCl solution after a wet/dry cyclic corrosion and continuous immersion test. The addition of Si nanoparticles increased the film resistance (R_f) and the charge transfer resistance (R_ct) of the coated steel. The surface analysis showed that uniform and fine Si-Fe complex oxides layers were formed acting as barrier layers that enhanced the corrosion protection of the coated steel in the wet/dry cyclic corrosion test. The results of the EIS of the coated steel with Si nanoparticles suggested that Si nanoparticles play a beneficial role in enhancing the corrosion resistance of organic coated steel.     

纯镁在1.0%NaCl中性溶液中的腐蚀与电化学行为(英文)

研究纯镁在1.0%NaCl中性溶液中的腐蚀行为及其相应的电化学阻抗谱(EIS)和极化曲线,探讨不同时间段EIS的分形维数。结果表明,腐蚀过程及相应的EIS发展可分为3个阶段。初始阶段,EIS由2个重叠的容抗弧组成,相应的极化电阻及电荷转移电阻随着时间的延长而快速增加,而腐蚀速率则降低。而后,EIS图谱上出现2个容易辨认的容抗弧,电荷转移电阻及腐蚀速率基本保持稳定。长时间浸泡后,EIS图谱中低频部分出现感抗成分,电荷转移电阻降低,而腐蚀速率增加。EIS分形维数与材料表面形貌直接相关,将是分析腐蚀形貌极有用的工具。     

Two‐step electrosynthesis of polypyrrole for corrosion protection of stainless steel

Smooth polypyrrole (PPy) films were successfully electrosynthesized on a stainless steel (SS, 1Cr18Ni9) surface by a self‐catalytic two‐step process. SS substrate dissolution during PPy electrosynthesis was effectively depressed. The redox properties and corrosion behavior of PPy film coated SS electrodes were investigated by cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization. The reduction of PPy was found to include two reaction processes: an anion dedoping process and a cation insertion process. The PPy film was found to lose its electroactivity when polarized at high potentials due to peroxidation. EIS of SS/PPy mainly corresponds to PPy film response and charge transfer resistance decreases as film thickness increases, indicating that SS corrosion can be inhibited effectively by the PPy film.     

Electrochemical behavior of titanium‐tantalum alloys in sulfuric acid solutions

Titanium exhibits a good corrosion resistance in oxidizing acids and neutral media but it is severely attacked in reducing acids. On the contrary, tantalum presents an excellent resistance in both oxidizing and reducing acids, but its high cost limits its use to very aggressive conditions. The titanium‐tantalum alloys are promising materials for use in reducing acids, due to their lower cost and density when compared to tantalum, and their higher corrosion resistance when compared to titanium. Titanium‐20, 40, 60 and 80 wt% tantalum alloys were prepared by arc‐melting and their microstructures were characterized by scanning electron microscopy and X‐ray diffractometry. Their electrochemical behaviors were studied in 20 to 80 wt% sulfuric acid solutions at room temperature, using open‐circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. Different behaviors were observed depending on the tantalum content and acid concentration. A clear tendency of increase in corrosion resistance with the increase of tantalum content is observed, especially in 80 wt% sulfuric acid solutions.     

Das Korrosionsverhalten von Tantal in heißer Salzsäure

Corrosion behaviour of tantalum in hot hydrochloric acid On account of its excellent resistance to corrosion and the high thermal conductivity tantalum is used in the chemical engineering industry. Used in hydrochloric acid at higher pressure and temperatures up to 200 °C localized embrittlements appeared, caused by a local increase of the hydrogen content. Loading tests in streaming hydrogen, by cathodic loading in different hydrochloric acid concentrations and different current densities as well as in the autoclave at 180 °C and hydrochloric acid concentrations up to 36% did not result in significant differences at electron beam melted or sintered material with different heat-treatments. Welding scams behaved analogous to the sheat-material, too. The electric conductivity shows a distinct dependance on the amount of hydrogen dissolved in the tantalum. To control a plant such measurements can be done on different tantalum parts to determine the amount of dissolved hydrogen.     

Untersuchungen zur Ta-Beschichtung von Stahl durch Vakuumplasmaspritzen

Investigations of tantalum coatings on steel by vacuum plasma spraying In this work the possibilities of the production of tantalum coatings by vacuum plasma spraying were investigated. Suitable parameters of the vacuum plasma spraying process were determined, and the quality of vacuum plasma sprayed tantalum coatings was evaluated with regard to chemical composition, adhesion strength, density and corrosion behaviour. To obtain high-quality coatings it was necessary to apply sufficient plasma power as well as an optimal injection of spraying powder into the plasma torch. A complete melting of the tantalum powder particles could not he achieved. The coatings obtained showed a good adhesion strength but a low formability (ductility). The corrosion resistance against HCL and HNO₃ was evaluated by curves of the current density versus potential. With the aid of the passive current density it was determined that the corrosion resistance of the sprayed coatings was not as excellent as of compact tantalum. The increased surface roughness was not significant with respect to the corrosion behaviour. The reduced corrosion resistance could be caused probably by a high oxygen content of the tantalum powder, especially by oxides around individual powder particles. In contrast to tantalum, vacuum plasma sprayed titanium coatings showed the same corrosion resistance as compact titanium under the same testing conditions.     

Effect of nitrogen ion implantation on the localized corrosion behavior of titanium modified type 316L stainless steel in simulated body fluid

Nitrogen ion implantation on titanium-modified type 316L stainless steel (SS) at the energy of 70 keV was carried out at different doses ranging from 1×10¹⁵ to 2.5×10¹⁷ ions/cm². These samples were subjected to open circuit potential (OCP)—time measurement, cyclic polarization, and accelerated leaching studies—in order to discover the optimum dose that can provide good localized corrosion resistance in a simulated body fluid condition. The results showed that the localized corrosion resistance improved with an increase in doses up to 1×10¹⁷ ions/cm², beyond which it started to deteriorate. The results of the accelerated leaching studies showed that the leaching of the major alloying elements was arrested upon nitrogen ion implantation. Gracing incidence x-ray diffraction studies showed the formation of chromium nitrides at a dose of 2.5×10¹⁷ ions/cm². X-ray photoelectron spectroscopy studies revealed the presence of these chromium nitrides in the passive film, which was attributed to the decreased corrosion resistance at a higher dose. Secondary ion mass spectroscopy studies on the passive film showed the variation in the depth profile upon nitrogen ion implantation. Thus, nitrogen ion implantation can be effectively used as a method to improve the corrosion resistance of the orthopedic implant devices made of titanium-modified type 316L SS. The nature of the passive film and its influence on corrosion resistance are discussed in this article.     

EIS Study on Interfacial Properties of Passivated Nitinol Orthodontic Wire in Saliva Modified with Eludril® Mouthwash

This work aimed at first-time use of EIS measurements to study the effect of ready-to-use Eludril® mouthwash containing 0.10% chlorhexidine digluconate as active component on corrosion performance of Nitinol orthodontic wire in artificial saliva at 37°C. In vitro corrosion resistance of the autoclaved Nitinol wire was studied under open circuit potential conditions using EIS combined with cyclic potentiodynamic polarization curves. HREM, SEM, EDS, and microhardness testing were used to study the properties of the Nitinol wire before and after corrosion measurements. EIS study of the interfacial properties of the Nitinol electrode | oxide layer | saliva solution system revealed the capacitive behavior of the material with high corrosion resistance. EIS allowed to determine resistance of charge transfer through the oxide | electrolyte interface. It was found that kinetics of pitting corrosion of the Nitinol electrode in saliva increases with the rising content of Eludril® mouthwash.     

Corrosion Properties of Cold-Sprayed Tantalum Coatings

Cold spraying enables the production of pure and dense metallic coatings. Denseness (impermeability) plays an important role in the corrosion resistance of coatings, and good corrosion resistance is based on the formation of a protective oxide layer in case of passivating metals and metal alloys. The aim of this study was to investigate the microstructural details, denseness, and corrosion resistance of two cold-sprayed tantalum coatings with a scanning electron microscope and corrosion tests. Polarization measurements were taken to gain information on the corrosion properties of the coatings in 3.5 wt.% NaCl and 40 wt.% H₂SO₄ solutions at room temperature and temperature of 80 °C. Standard and improved tantalum powders were tested with different spraying conditions. The cold-sprayed tantalum coating prepared from improved tantalum powder with advanced cold spray system showed excellent corrosion resistance: in microstructural analysis, it showed a uniformly dense microstructure, and, in addition, performed well in all corrosion tests.     

The effect of ion implantation on the corrosion behaviour of pure iron-III. Tantalum ion implantation

Pure iron specimens were implanted with doses of 5 × 10¹⁴ and 2 × 10¹⁵ tantalum ions/mm². Using a three sweep potentiokinetic polarization technique the corrosion behaviour of these surface alloy layers was compared with that of pure iron and of a conventional Fe-4.9 wt% Cr alloy. It was found that tantalum implantation improved the corrosion resistance of pure iron and in particular reduced both the critical current density for passivation and the passive current density. The corrosion resistance of tantalum implanted iron was similar to that of the conventional Fe-4.9 wt% Cr alloy. The beneficial effects of tantalum implantation were unexpectedly persistent.     

Corrosion rate of construction materials in hot phosphoric acid with the contribution of anodic polarization

The paper is focused on selection of a proper material for construction elements of water electrolysers, which make use of a 85% phosphoric acid as an electrolyte at temperature of 150 °C and which might be loaded with anodic polarization up to 2.5 V versus a saturated Ag/AgCl electrode (SSCE). Several grades of stainless steels were tested as well as tantalum, niobium, titanium, nickel alloys and silicon carbide. The corrosion rate was evaluated by means of mass loss at free corrosion potential as well as under various levels of polarization. The only corrosion resistant material in 85% phosphoric acid at 150 °C and at polarization of 2.5 V/SSCE is tantalum. In that case, even a gentle cathodic polarization is harmful in such an acidic environment. Hydrogen reduction leads to tantalum hydride formation, to loss of mechanical properties and to complete disintegration of the metal. Contrary to tantalum, titanium is free of any corrosion resistance in hot phosphoric acid. Its corrosion rate ranges from tens of millimetres to metres per year depending on temperature of the acid. Alloy bonded tantalum coating was recognized as an effective corrosion protection for both titanium and stainless steel. Its serviceability might be limited by slow dissolution of tantalum that is in order of units of mm/year.     

Peculiarities of electroplating tantalum coatings from fluoride melts

Electroplating tantalum coatings on molybdenum, copper, and steel is studied. The effects of various factors (the composition of a fluoride bath, its temperature, current density, and the electric charge spent) on the electrocrystallization of the deposit, its roughness, the degree of dendrite formation, current efficiency, and a possibility to plate multilayer coatings and produce tantalum wares by electrotyping are investigated. To compare the characteristics of the coatings, the studies in a standard chloride-fluoride salt system containing potassium fluorotantalate (K₂TaF₇) were also carried out under similar conditions. Original Russian Text ? V.A. Pavlovskii, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 3, pp. 303–306.     

Korrosionsuntersuchungen an Niob-Tantal-Legierungen

Corrosion research on niobium-tantalum alloys Following a discussion of the mechanical and electrical properties of niobium, tantalum and their alloys, the corrosion behaviour of these metals in different mineral acids and in potash lye is reported upon. It is shown that tantalum can be largely replaced by niobium through alloying without losing any of its high corrosion resistance to aqueous solutions. This knowledge should lead to a much wider application of the rare and expensive metal tantalum.     

钽及表面离子渗氮层的耐碱腐蚀性

应用弱极化区三点法和线性极化法对钽及表面离子渗氮层在10％－NaOH中的腐蚀电流和极化电阻进行了测量，给出了腐蚀电流与离子渗氮工艺之间的回归方程。     

Bestimmung der Abtragungsraten von Zirconium,Tantal und der Legierung Tantal-40Niob in fluoridhaltiger azeotroper Salpetersäure mit Hilfe der Radiotracer-Methode

The radiotracer technique as a means to investigate the corrosion of zirconium, tantalum, and a Ta-40Nb alloy in fluoride containing azeotropic nitric acid Zirconium and tantalum as well as the tantalum 40% niobium alloy are of considerable technical importance due to their high corrosion resistance against numerous corrosive media. With respect to corrosion testing in analytically pure azeotropic nitric acid in the temperature range between 20 and 121°C, corrosion rates were determined for zirconium: 7 · 10^?6 to 5 · 10^?4 mm/y, for tantalum: 10^?8 to 4 · 10^?6 mm/y, and for the Ta-40Nb alloy: 2 · 10^?7 to 8 · 10^?6 mm/y [1]. These corrosion rates will be markedly increased by adding small amounts of fluorides or by fluoride impurities. The radiotracer method after neutron activation was applied to determine the corrosion rates in azeotropic fluoride containing nitric acid. Even minute additions of fluorides strongly affect the corrosion resistance of zirconium. In the range between 0.15 and 10 ppm F^? and at a temperature of 108°C, corrosion rates between 5.3 · 10^?3 and 3.1 mm/y were measured. It was impossible to establish a limit for the fluoride concentration, below which the corrosion rate of zirconium will not be adversely influenced. The corrosion rates of tantalum and the Ta-40Nb alloy are considerably increasing above a fluoride concentration of 10 ppm. The highest corrosion rates measured were between 8.4 · 10^?3 mm/y at 50°C/280 ppm F^? and 1.4 · 10^?2 mm/y at 110°C/320 ppm F^?. Within the range of this investigation, the corrosion resistance of tantalum was higher than that of the Ta-40Nb alloy by one order of magnitude. The corrosion resistance of zirconium and tantalum was not influenced by any treatment of the samples before testing.     

增材制造钽及多孔钽的研究进展

金属钽是一种具有优异耐腐蚀性、生物相容性和介电性能的难熔金属材料,因而被广泛应用于高温技术、电子技术、耐腐工程、原子能以及医疗等行业。增材制造技术能够实现复杂钽金属零件的一体化成形,并且材料利用率高、可实现个性化定制。本文介绍了增材制造用球形金属钽粉的研究现状,评述了钽金属粉末及增材制造成形后的组织和性能研究及应用进展,分析了钽金属增材制造技术当前存在的一些问题,并对该技术的未来发展进行了展望。     

Microstructural evolution and localized corrosion resistance of an aged superduplex stainless steel

The present investigation was undertaken to analyze the effects of isothermal ageing treatments, carried out between 700 and 900 °C for a variety of times up to two weeks and followed by water quenching, on the microstructure and on the localized corrosion resistance of a superduplex stainless steel, SAF 2507.The quantitative metallography coupled with X-ray diffraction techniques was adopted to follow the microstructural evolution, together with SEM microscopy.Electrochemical potentiodynamic tests, as cyclic polarization curves recorded in sodium chloride solutions, together with weight loss measurements were employed to evaluate the susceptibility of the aged specimens to pitting corrosion.The influence of the transformation of ferrite into secondary austenite and sigma phase and of other microstructural variations, as chromium nitrides precipitation, on the stability of the passive film is shown. The susceptibility of the aged alloy to pitting corrosion phenomena, is related to sigma phase precipitation in association to the secondary austenite formation, which lead to a noticeable Cr depletion at grain boundaries.