Atmospheric corrosion of copper and some copper alloys

Abstract

Two-year atmospheric corrosion tests in an urban environment were conducted on specimens of copper, Muntz metal, and copper-zinc-aluminum alloys. X-ray diffraction and X-ray spectrographic studies were made of the films on the top surface and underside of the exposure coupons which were exposed facing south but inclined at a 45° angle to the vertical. Differences between the two surfaces are attributed to the leaching action of rain as well as the possible effect of direct sunlight. The corrosion products of copper were found to consist predominantly of Cu₂O, but also included a substance of undetermined composition, copper chloride and basic copper chloride. The zinc-containing alloys formed similar products, along with zinc sulphates, and showed considerable dezincification. A preoxidation treatment improved the tarnished appearance of the ternary alloy.

Résumé

Des essais de corrosion atmosphérique en milieu urbain ont été exécutés sur du cuivre, du métal Muntz et des alliages Cu-Zn-Al. Les échantillons étaient placés à un angle de 45°, face au sud et des mesures de diffraction aux rayons-X et de spectrographie X ont été faites sur chacune des faces. Les differences entre les deux faces d'un même échantillon peuvent étre attribuables à la pluie et peut-être aussi au solell. Les produits de corrosion du cuivre sont surtout formés de Cu₂O et également du chlorure de cuivre, du chlorure basique de cuivre et un composé non identifié sur les alliages contenant du zinc des produits semblables se sont formés avec aussi des sulfures de zinc; on y notait aussi une dézincification. Dne oxydation avant les essais améliorait l'apparence finale des alliages ternaires.     

Densities of liquid Fe-Ni and Fe-Cr alloys

Formerly Graduate Student, Department of Materials Science and Engineering, Carnegie Mellon University.     

The oxidation behavior of some Ni-Cr-Al alloys at high temperatures

Oxidation of ternary Ni-Cr-Al alloys containing different Cr/Al ratios has been studied in the temperature range 800° to 1300°C. Most of the studies were performed in 1 atm oxygen or air, but the oxygen pressure dependence for one of the alloys was also investigated. The experimental methods included thermogravimetric measurements of oxidation rates and studies on reacted specimens by means of X-ray diffraction, metallographic techniques, electron microprobe analysis, and electron microscopy. In general, the oxidation rates decrease faster with time than that for an ideal parabolic behavior. The major reaction products were NiO, Cr₂O₃,α-Al₂O₃, and Ni(Cr,Al)₂O₄. The relative amounts of these were a function of composition, temperature, oxygen pressure, and reaction time. The Ni-9Cr-6Al alloy has the best oxidation resistance due to the formation ofα-Al₂O₃ at all temperatures investigated. The oxidation mechanism of the alloy is discussed.     

航空Al-Cu-Mg合金剥落腐蚀行为

采用TEM、电化学等分析方法和手段,对在剥落腐蚀溶液中浸泡不同时间的Al-Cu-Mg合金的剥蚀敏感性及电化学阻抗(EIS)进行研究,分析剥落腐蚀的动力学过程.实验结果表明,2524-T4态合金具有良好的耐剥落腐蚀性能,高Cu含量的第二相粒子是影响合金剥蚀行为的主要因素,合金浸泡2d后才可见明显的点蚀,浸泡4d后局部出现剥蚀现象.根据EIS及EIS等效电路的拟合分析合金的剥蚀行为,发现其动力学过程主要由点蚀的诱导形成、点蚀发展及轻微的剥蚀形成三个阶段组成,而腐蚀的界面反应依次经历氧化膜的溶解、表面腐蚀产物的形成、吸附及脱落的一系列过程.     

Fe-Cr钢在空气中的氧化行为

为了测定不同质量分数的铬元素对钢高温氧化行为的影响,采用热重法对Fe-5Cr钢与Fe-10Cr钢在800～1 200℃下进行高温氧化研究。建立了两钢种的氧化动力学模型,计算出了两钢种的激活能。利用金相显微镜和X射线衍射对两钢种氧化后的断面形貌和物相进行了分析。结果表明,两钢种的高温氧化动力学曲线遵循抛物线规律,Fe-5Cr钢的激活能小于Fe-10Cr钢。800℃下,Fe-5Cr钢生成不连续的氧化铁皮,Fe-10Cr钢氧化铁皮极少部分形核。900～1 200℃下,氧化铁皮结构由外向里依次为Fe₂O₃、Fe₃O₄和Cr₂O₃。由于Cr₂O₃的阻碍作用,氧化铁皮中没有发现FeO。由于高温和高氧分压,Cr₂O₃失效,导致两钢种在1 000～1 200℃下具有相似的氧化速率。     

Contact interaction of double titanium and chromium diboride with Fe-Cr alloys

The kinetics of wetting double titanium and chromium diboride by iron-based alloys with different chromium content is studied. It is shown that contact angles are formed in such systems over the range 0–10°. The energy parameters of wetting are calculated. It is established that chromium as a surface-active element promotes Fe-Cr alloy spreading on the diboride surface. The microstructure of the interaction area is studied. It is shown that terminal solid solutions and eutectics are formed in the TiCrB₂-(Fe-Cr) system. The optimum compositions of the metallic binder are determined for TiCrB₂-based composite materials. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 109–115, 2007     

Ni-Cr-Mo-Cu-Mx合金耐晶间腐蚀及点蚀性能

向镍基耐蚀合金中添加Ti、Fe元素,采用手工电弧炉熔炼制备新型Ni-Cr-Mo-Cu-Mx耐蚀合金,用化学浸泡法、电化学法(极化曲线法、循环伏安法)对其耐晶间腐蚀和耐点蚀能力进行研究.结果表明:在Ni-Cr-Mo-Cu合金中加入Ti元素可以增强其耐晶间腐蚀能力,减弱其耐点蚀的能力;加入Fe元素会降低Ni-Cr-Mo-Cu合金耐晶间腐蚀的能力,但提高该合金耐点蚀的能力;实验合金晶间腐蚀与点蚀的电化学行为和特征与其浸泡腐蚀的结果是吻合的.     

Effect of solidification microstructure on corrosion behavior of the chill zone in aluminum binary alloys

The corrosion behavior in NaCl solutions of as-cast Al-Cu, Al-Mg and Al-Zn alloys has been studied in relation to the substructures obtained during the solidification process on the surface of the chill zone. Metallographic, microprobe and X-ray techniques have been used to identify the equilibrium precipitates and to estimate the solute distribution in the alloys. The attack produced on predendritic, dendritic and interdendritic zones has been studied by optical microscopy and by scanning electron microscopy. By using potentiostatic techniques, it has been found that localized corrosion occurred above certain potentials corresponding to the pitting potentials of the phases present in the alloys.     

Effect of solidification microstructure on corrosion behavior of the chill zone in aluminum binary alloys

The corrosion behavior in NaCl solutions of as-cast Al-Cu, Al-Mg and Al-Zn alloys has been studied in relation to the substructures obtained during the solidification process on the surface of the chill zone. Metallographic, microprobe and X-ray techniques have been used to identify the equilibrium precipitates and to estimate the solute distribution in the alloys. The attack produced on predendritic, dendritic and interdendritic zones has been studied by optical microscopy and by scanning electron microscopy. By using potentiostatic techniques, it has been found that localized corrosion occurred above certain potentials corresponding to the pitting potentials of the phases present in the alloys.     

The effect of aluminum content on the corrosion behavior of Fe-Al alloys in reducing environments at 700 °C

The high-temperature corrosion behavior of monolithic Fe-Al alloys, with 0 to 20 wt pct Al, was investigated at 700 °C in a reducing atmosphere (p(S₂) = 10⁻⁴ atm, p(O₂) = 10⁻²⁵ atm) for up to 100 hours. Postexposure characterization of the corrosion reaction products consisted of surface and cross-sectional microscopy, in combination with energy dispersive spectroscopy, electron probe microanalysis, and quantitative image analysis. From the kinetic data, three stages of corrosion behavior (i.e., inhibition, breakdown, and steady state) were found with the observance and/or duration of each stage directly related to the aluminum content of the alloy. The first stage, labeled the inhibition stage, was characterized by low weight gains and the absence of rapid degradation of the alloy. Typically observed for compositions with 10 to 20 wt pct Al, protection was afforded due to the development of a thin, continuous alumina scale. For alloys with 7.5 wt pct A1, the ability to maintain the initially formed alumina scale was not observed, resulting in the breakdown stage. Localized corrosion product nodules, containing iron sulfide (Fe_1-x S) and the spinel-type tau phase (FeAl₂S₄), developed through the alumina scale due to sulfur short-circuit diffusion. These growths were accompanied by relatively high corrosion rates. Further decreasing the aluminum content to 5 wt pct and below lead to the formation of a continuous sulfide scale whose growth was controlled by iron and sulfur diffusion through the previously formed product. The alloy wastage rates in the steady-state stage were relatively high when compared to the previous two regions.     

Stress corrosion cracking of aluminum alloys

Stress corrosion cracking of aluminum alloys is reviewed. An extensive failure analysis shows how many service failures occurred in the aerospace industry over a ten year period and what kind of alloys and stresses led to initiation and propagation of stress corrosion cracks which caused these service failures. The paper contains most of the results of stress corrosion tests with aluminum alloys that have been obtained to date with fracture mechanics techniques. Stress corrosion crack growth rate measurements are compared with the results from smooth specimen testing and it is shown that the correlation between the different test results is very satisfactory. The present and limited status of theoretical understanding of stress corrosion cracking is outlined. A major part of the paper is devoted to the results of the latest alloy development. High strength aluminum alloys of dramatically increased stress corrosion resistance are available now. In the near future, stress corrosion resistant alloys of even higher strength might become available. What is still lacking is a detailed understanding of the mechanisms by which stress corrosion cracks initiate and propagate.