Stress corrosion cracking of copper and silver, specific effect of the metal cations

Based on stress corrosion cracking (SCC) studies on brass, and on Ag-Cd alloys (a model alloy used to reproduce the behaviour of brass), it was found that both pure copper and pure silver are susceptible to SCC in 1 M copper(II) nitrate and in 1 M silver nitrate aqueous solutions, at the equilibrium potentials for the reactions: Cu²⁺+2e⁻↔Cu and Ag⁺+e⁻↔Ag, respectively. The results were analysed under the light of recent developments in surface science. It was concluded that the same SCC mechanism that operates in brass and in Ag-Cd alloys should be operating during SCC of pure copper and pure silver, under equivalent experimental conditions.     

The stress-assisted dezincification of 70/30 brass in ammonia

Zinc and copper losses from 70/30 brass specimens tensile loaded to various stress levels and exposed to 10 N NH₄OH were estimated at different time intervals by atomic absorption spectroscopic analysis of the corrodent. Dissolution of each element was found to be accelerated with increasing tensile stresses. The preferential dissolution of Zn was also found to increase with stress and a maximum in the dezincification occurred at about 105 MPa. Corrosion of the brass as a whole, however, increased monotonically with stress. Applied stresses altered the open circuit potential of the brass by a maximum of ±10⁻¹ mV MPa-1, and its potentiostatic polarization curve was shifted to higher current densities. The depth of dezincification for short intervals calculated from the present results showed that dezincification could be a viable mechanism for transgranular stress corrosion cracking of brasses.     

Örtliche Korrosion von Komponenten aus Messing MS 58 in der Trinkwasser-Installation

Localized corrosion of yellow brass 58 in tap water installation Yellow brass material with 58 wt.-% Cu is subjected to dezincation and cracking in tap water. Both kinds of corrosion are enhanced by tensile stresses and by anodic polarisation resp. oxygen content of the water. Furthermore, the water type has an effect, where - according to this investigation – the chloride content is of interest. The presence of critical components for SCC (such as NH₃) are not necessary. In the case of mixed installation with tubing of inert material (such as stainless steel or plastics) the corrosion likelihood is increased in comparison to galvanised steel or copper because of oxygen consumption by corrosion of the latter materials. Bimetallic corrosion in mixed installation with stainless steel does not take place. Failures of components of domestic installations by corrosion should be prevented by using a material having a higher resistance to dezincation.     

The correspondence between susceptibility to SCC of brass and corrosion-induced tensile stress with various pH values

Corrosion-induced stress and susceptibility to stress corrosion cracking (SCC) of brass in an ammonia solution with various pH values have been studied. pH value dependence of corrosion-induced stress measured by two different methods showed a good agreement, and was correspondent to that of susceptibility to SCC. When pH?8, with increasing pH value, the corrosion-induced tensile stress had a maximum value and hardly changed; at the same time, the susceptibility to SCC exhibited a maximal value and a slight change. However, when pH?6, with decreasing pH value, both the corrosion-induced tensile stress and the susceptibility to SCC reduced rapidly. So, the SCC of brass in an ammonia solution was in close relationship with the corrosion-induced stress.     

Stress corrosion cracking and selective corrosion of copper-zinc alloys for the drinking water installation

Despite a generally good corrosion resistance to tap and industrial water, many brass taps and fittings have failed in the past by stress corrosion cracking (SCC) and selective corrosion (dezincification or preferred removal of a phase). The experimental investigations of the present study clarify the influence of the ammonia concentration on the two types of corrosion. Notched specimens made of the alloys CuZn39Pb3, CuZn40Pb2, CuZn37, CuZn36Pb2As and CuZn21Si3P are polarized anodically in pure tap water and tap water with realistic ammonia concentrations (15 and 30 ppm) under a simultaneous mechanical loading condition. The influence of stress and of the third alloying elements lead and arsenic are investigated and evaluated. The experiments show that the ammonia additions significantly increase the risk of dezincification of the α-β-brasses. The arsenic in the CuZn36Pb2As alloy avoids dezincification, but enhances the risk of SCC. The rate of selective corrosion and SCC consistently increases with increase in tensile stress.     

黄铜应力腐蚀敏感性及其与脱Zn层拉应力的对应性

测量了不同极化电位下,Ｈ６２黄铜在氨水溶液腐蚀过程中表面脱Ｚｎ蔬松层引起的拉应力,并用单边缺口试样测量的不同极化电位下的应力腐蚀敏感性,结果表明：黄铜在氨水中自然腐蚀时,在脱Ｚｎ层界面会产生 大的拉应力,整个试样的平均应力为σ＝１８．１ＭＰａ;阳极极化使表面拉应力略有下降,阴极极化则使疏松层引起的拉应力急剧下降乃至为零,阴极极化在表层产生镀Ｃｕ层后出现尖力;应力腐蚀敏感性随外加电位的变化规律和疏松     

Chemical composition of new copper alloys for machining and its effect on their susceptibility to corrosion cracking

Zinc‐containing copper alloys, the so‐called α + β brasses, are commonly used in contact with potable water. These materials are alloyed with lead to improve machinability. In wrought special brass alloys, reducing the content of this alloying element or replacing it with alternative alloying additions may give rise to a new type of machinable copper alloys which differ from the original alloys by their contents of other modifier elements such as Si (or possibly, Mg, Bi, and P). These alloys have a very low content of lead required for the break‐up of chips during machining. Even though these types of brass exhibit a very good machinability, the effects of their chemical composition on the resistance of the alloy to corrosion cracking have not yet been given sufficient attention. This paper aims to present an assessment of three new types of machinable copper alloys regarding their susceptibility to stress corrosion cracking, in comparison to that of the lead‐alloyed variety, in 0.05 M NaCl, NaNO₂, and Na₂SO₄ solutions. The slow strain rate test has been used for this purpose, and its results were correlated with metallographic evaluation of the number and depth of the cracks observed on the test specimen surfaces on completion of the test.     

Influence of P,As and Sb on the susceptibility to SCC of α-β′ brasses

The influence of P, As and Sb on the susceptibility to SCC of α-β′ brasses in different non ammoniated solutions was studied. Two series of brasses were tested: the first one with only 5 – 10% of β′ phase and the second one with 54 – 56% of β′ phase. The VB group elements were present at two different concentrations. Susceptibility to SCC was evaluated by SSRT, at a strain rate of 1 × 10⁻⁶ s⁻¹, in concentrated (1M) or diluted (50 and 200 ppm) solutions of Na₂SO₄, NaNO₂, NaCl, at room temperature. The brasses of second series were found to be more susceptible to SCC than those of the first series in all the environments studied. Sb drastically increased SCC susceptibility of the brasses of the first series, while As showed a beneficial effect. The three VB group elements produced a limited inhibiting effect on susceptibility to SCC in the second series of brasses. Susceptibility to SCC of all the brasses was compared with the tendency to dezincification, measured by means of the 6509 ISO Standard Test. The influence of the VB group elements on the two types of corrosion was not comparable.     

Corrosion of Aluminium—Literature Review 1965–1967

Abstract

Lewis and others report that stress-corrosion cracking and intercrystalline corrosion are the main problems associated with the aluminium alloys used in the aircraft industry. Stress-corrosion cracking occurs principally in the joints of integrally machined sections, and in forgings, as a result of the combination of stresses such as residual heat treatment stresses, airborne versus ground stresses and assembly stresses together with any corrosive environment combined with inadequate protection; in some susceptible alloys the stress corrosion takes the form of end grain attack at the radii of integrally machined sections. Intercrystaliine corrosion has also been a major problem both in the aircraft industry as well as industry in general. In the latter case the corrosion is sometimes attributed to misapplication and lack of care during handling or pretreatment.     

氢对黄铜脱锌层引起拉应力的影响

黄铜表面在氨水中腐蚀或应力腐蚀时形成脱锌层 ,由此产生一个附加拉应力。实验结果表明 ,脱锌层拉应力σp 随黄铜试样中氢含量w(H)的升高而线性升高 ,即σp/MPa =13.2 5 .2× 10 -6w(H)。黄铜中的氢含量达到 3× 10 -6时 ,可使黄铜在氨水中的应力腐蚀敏感性升高 10 %。氢促进黄铜应力腐蚀的原因是氢含量的增大会引起脱锌层拉应力的增大。     

氢促进黄铜应力腐蚀及升高脱锌层应力的一致性

黄铜在氨水中腐蚀或应力腐蚀时表面形成脱锌层，它会产生一个会加拉应力，用挠度法和和流和差值法测量了不同氢浓度试样的脱锌层所引起的附加应力，也研究了不同氢浓度试样在氨水中的应力腐蚀敏感性，慢应变速率拉伸表明，黄铜不显示氢脆，但在氨水中显示极高的应力腐蚀敏感性（ISCC），它随试样中氢浓度（C0）升高而升高，脱锌层拉应力σp也随试样中氢浓度的升高而升高，实验表明，应力腐蚀敏感性随氢浓度的变化和脱锌层拉应力随氢浓度的变化相一致。     

Effect of cutting process on the stress corrosion susceptibility of AISI 304L stainless steel

During manufacturing of a component, cutting, turning, grinding, and milling operations are inevitable and these operations induce surface residual stresses. In this study, it is shown that, depending on the process employed for cutting, residual stresses generated at the cut surfaces can vary widely and they can, in turn, make the cut surfaces of austenitic stainless steel (SS) prone to stress corrosion cracking (SCC). An austenitic SS 304L plate was cut using three different procesess: bandsaw cutting, cutting using the cut-off wheel, and shearing. Surface residual stress measurement using the X-ray diffraction (XRD) technique is carried out close to the cutting edges and on the cross-section. SCC susceptibility studies were carried out as per ASTM G36 in 45% boiling magnesium chloride solution. Optical microscopic examination showed the presence of cracks, and confocal microscopy was used to measure the depth of cracks. The study confirmed that high tensile residual stresses present in the cut surfaces produced by cut-off wheel and shear cutting make the surfaces susceptible to SCC while the surfaces produced by bandsaw cutting are resistant to SCC. Hence, it is shown that there is a definite risk of SCC for product forms of austenitic SS with cut surfaces produced using cutting processes that generate high tensile residual stresses stored for a long period of time in a susceptible environment.     

Anodische Polarisationskurven von Messinglegierungen in Ammoniumchloridlösungen

Anodic polarization curves of brass alloys in ammonium chloride solutions Potentiodynamic investigations have revealed, that curves traced during the low rate polarization characterize the anodic behaviour of brasses. Such curves show that copper-rich alloys behave in a way analogous to that of copper. It is consequently possible from the polarization curves of copper to derive the behaviour of such alloys. Zinc- rich alloys behave like zinc at the beginning but during the dissolution process a new copper-rich phase is probably formed and the behaviour is then comparable to that of copper-rich alloys. Alloys of h&h copper content can be passivated, but passivation current and potential grow as the zinc con- tent is increased.     

Cu-Al-Be形状记忆合金的应力腐蚀性能

用恒载荷法和慢应变速率法及SEM研究了Cu-Al-Be形 状记忆合金在甘油、海水和氨介质中的应力腐蚀性能.结果表明，Cu-Al-Be合金具有良 好的抗海水应力腐蚀性能和较低的氨介质应力腐蚀倾向.单相马氏体有较 好的耐海水腐蚀能力，可减少腐蚀引起的裂纹源；外应力下马氏体的孪晶变形和变体间的界 面迁移，则有利于松弛应力集中，阻碍和延缓腐蚀裂纹源的扩展，从而提高Cu-Al-Be合金的 应力腐蚀能力.     

The chloride stress-corrosion cracking behavior of stainless steels under different test methods

Chloride-induced stress-corrosion cracking (SCC) is one of the failure modes of stainless steels. Highly alloyed austenitic stainless steels S32654, S31254, and N08028, and duplex grades S32750 and S31803 possess much improved resistance to SCC compared with S30400 and S31600 steels. With the development of a database, SSData, experimental data collected from calcium chloride tests, autoclave tests, and drop evaporation tests were evaluated. Stress-corrosion cracking data generated by autoclave tests agreed well with the practical service conditions and can be used to discriminate alloys for SCC resistance in sodium chloride solution. Drop evaporation test data can be used in situations where evaporation may occur and cyclic loading may be involved. The SCC resistance of alloys under each method increased with increasing molybdenum equivalent Mo + 0.25Cr + 0.1Ni. For a given alloy, the testing result depends on the stress state and environment; different test methods can give different ranking orders concerning SCC resistance. The performance of duplex stainless steels in a chloride-containing environment at higher temperatures was not as good as expected when dynamic loading was involved.     

The resistance to stress corrosion cracking of some Cr–Ni–Fe austenitic steels and alloys

Abstract

Stress-corrosion cracking testing by a variety of methods has been carried out in chloride and caustic environments on a series of Cr–Ni–Fe austenitic steels and alloys containing between 10 and 25 % of chromium and 15 and 45% of nickel. Limited testing has also been carried out on alloys containing additions of molybdenum and copper. The tests have confirmed that increasing the nickel content reduces the susceptibility of Cr–Ni–Fe alloys to stress-corrosion cracking in chloride solutions. Chromium content also affects cracking susceptibility but to a lesser degree. Stress corrosion susceptibility in caustic solutions is affected by these alloying elements in a different way. The results are discussed in relation to currently proposed theories of stress-corrosion cracking.     

Anodic Dissolution and Selective Corrosion of Alloys

The mechanisms of the anodic dissolution of alloys are considered. The kinetic explanation of an abrupt increase in the corrosion resistance of the alloys, formed by metallic systems with a continuous series of solid solutions, is given. The dezincification of brasses related to the reduction of the oxidation products of copper is accounted for by the chemical conjugation of the partial ionization reactions of zinc and copper. The former reaction transmits a part of the free energy to the latter one via vacancies. As a result, the ionization of copper becomes possible at the potentials below the equilibrium potential of the individual copper. For the same reason, the oxidized copper can reduce at the brass surface to the individual copper phase. The mechanisms of the dissolution of intermetallides, used for obtaining skeleton catalysts, are discussed.     

Stress corrosion cracking of noble metals and their alloys in solutions containing cations of the noble metal: Review of observations relevant to competing models of SCC

The stress corrosion cracking of Ag, Au and Cu-base alloys, and of pure Ag and Cu, has been studied by J.R. Galvele and others. These authors used solutions that contained the cation of the more-noble metal, so that the tested specimen was at or close to its equilibrium potential in the given solution. The opportunity is taken to review the history of this far-from-new observation and some of its implications. The role of the exchange current density in such cracking is discussed. Observations of Sieradzki and Torchio are used to suggest that in alloys such as brass, SCC is favoured by low,nothigh,surfacemobility, in line with the film-induced cleavage model, which requires very fine nanoporosity at the crack tip - such a favourable condition can only be achieved if dealloying is either very fast or occurs under conditions of low surface mobility. Observations of very slow intergranular SCC in pure metals under dynamic loading are interesting, but not really suggestive of mechanistic continuity with the dramatic mixed-mode cracking that occurs under static loading in brass or AuAg alloys. Torchio’s observations on brass U-bends in CuSO₄ solutions of various pH and Cu²⁺ concentrations are particularly hard to interpret using the surface mobility model.     

A centennial: Evolution in the understanding of chemical ordering in metallic crystals

Many important metallic alloys are characterised by the chemical ordering of their atomic component elements. Examples are beta brass (βCuZn – one of the components of common brass), many of the gold-base alloys used in dentistry, Nickel–Titanium shape memory alloys with superelastic properties (great stretchability, as used for orthodontic wires) and Nickel–Aluminium gamma-prime phase which strengthens superalloys for high-temperature turbines. The figure shown below (Fig. 1) represents such an ordered arrangement of two atomic species (could be copper and gold, or nickel and aluminium) on a face centred cubic lattice. The disordered lattice would have the yellow and blue atoms randomly distributed.While such important materials, the realisation that these crystals are chemically ordered (in contrast to chemically-disordered alloys, such as alpha brass (αCuZn), steels, aluminium alloys, and most other metallic alloys) is a relatively new understanding, being just now one century old. It had been understood for a long time before that crystals contained spatially-ordered atoms, but not that there was chemical order hidden inside. It was only with the development of methods of diffraction of x-rays by crystals that it became possible to recognise and quantify such chemical order.     

Two distinct fracture modes of copper alloys in fluoride environments

The susceptibility of aluminum brass and aluminum bronze to stress corrosion cracking (SCC) was evaluated in fluoride environments by means of the slow strain rate technique. The effects of fluoride concentration and applied electrochemical potential on the SCC susceptibility were investigated. The SCC mechanism of aluminum brass was found to be dependent upon the de-alloying phenomenon while that of aluminum bronze on the film-rupture mechanism occurring within a certain range of applied electrochemical potentials. For aluminum brass, both the stress ratio and the time-to-fracture ratio were closely related to the logarithmic concentration of F⁻ ions. The fracture modes were ductile dimpled tearing fracture for the aluminum brass at the corrosion potential while intergranular for the aluminum bronze at various anodic potentials. The micro-galvanic effects of the constituent elements were used to estimate the anodic equilibrium potentials of the two alloys.