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.     

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     

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.     

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.     

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. Brown Boveri Research Center, Baden, Switzerland This paper is based on an invited presentation made at a symposium on “Advances in the Physical Metallurgy of Aluminum Alloys” held at the Spring Meeting of TMS-IMD in Philadelphia, Pennsylvania, on May 29 to June 1, 1973. The symposium was co-sponsored by the Physical Metallurgy Committee and the Non-Ferrous Metals Committee of TMS-IMD.     

The role of microstructure in localized corrosion of magnesium alloys

The article presents new findings on the influence of microstructural changes on corrosion behavior of magnesium alloy AZ91 in chloride solution, with a particular attention to the role of the β phase (Mg₁₇Al₁₂) and the surrounding Al-rich-α area. The as-cast alloy was subjected to solutionizing and aging heat treatments, in order to incorporate variation in morphology and distribution of the intermetallic β phase and the surrounding Al-rich-α (also known as eutectic α). Although previous workers have ascribed the higher corrosion resistance of a fine-grained alloy to the formation of the finely distributed β phase, the present work suggests that it is the ratio of the β phase to the Al-rich-α that governs the localized corrosion of the aged alloy. Corrosion characteristics were investigated by immersion and electrochemical tests. Surface microtopography, optical microscopy, and scanning electron microscopy (SEM) were employed to characterize the localized corrosion.     

The rate of absorption of hydrogen into iron and of nitrogen into Fe-Cr and Fe-Ni-Cr alloys containing sulfur

The rate of absorption of hydrogen into liquid iron and of nitrogen into liquid Fe-Cr alloys containing various levels of sulfur was measured by using a constant-volume Sieverts apparatus employing a sensitive pressure transducer. The rate for the absorption of hydrogen was measured by using H2 containing a small amount of H₂S(<0.2 pct) such that the activity of sulfur on the surface of the melt was the same as in the bulk metal. The hydrogen-absorption rate for Fe-S melts containing up to 0.72 pet sulfur was virtually independent of sulfur content and controlled by liquid-phase mass transfer. The liquidphase mass-transfer coefficient for hydrogen in liquid iron, calculated from the results, was comparable to that for nitrogen transfer in liquid iron. The rate of absorption of nitrogen into Fe-Cr melts with low-sulfur contents was controlled by liquid-phase mass transfer. For melts containing significant amounts of sulfur it was controlled by both mass transfer and the chemical rate of the dissociation of nitrogen on the surface in series. Equations were developed to calculate the chemical rate from the measured rate, correcting for mass transfer. The chemical rate decreased with increasing sulfur content as expected, because sulfur is strongly adsorbed on the surface and increased with chromium content at constant sulfur activity, possibly because available Cr sites promote nitrogen dissociation. Formerly with United States Steel Corporation, Monroeville, PA     

In vitro corrosion measurements of dental alloys

Unguided protrusive and retrusive mandibular movement was investigated in 76 asymptomatic volunteers and temporomandibular joint (TMJ) patients using computerized axiography. In 38 of these subjects, guided pro-/retrusion was also recorded. Measurements were performed in a three-dimensional Cartesian coordinate system (x = anteroposterior; y = transversal, toward the hinge axis; z = craniocaudal). Transversal shift (y) was measured and evaluated as well as the distance "s" and horizontal condylar inclination (HCl) at the point of maximum transversal deviation. The patterns of the tracings were analyzed with a view to diagnostic improvements. The objective of this study was to evaluate transversal shift and to examine the postulate of symmetrical behavior of the TMJs in pro-/retrusion. The mean mandibular shift was 0.15 mm to the left. This maximum deviation was seen in a mean distance "s" of 7.42 mm in relation to the Cartesian coordinate system in reference position. These results suggest a functional dominance of the right part of the mandible in protrusive and retrusive movement.     

Al-Zn-Mg系铝合金应力腐蚀性能

研究了热处理制度和时效工艺的改变对Al-Zn-Mg系铝合金的组织结构、力学性能和应力腐 蚀性能的影响。研究结果表明:高温预析出可以改变Al-Zn-Mg系铝合金晶界的析出相大小和分 布,从而改善其抗应力腐蚀性能;在T6和T612种人工时效条件下,预析出的合金的抗应力腐蚀 性能均好于无预析出的合金。在自然时效状态下,引入超声波,对无预析出合金的应力腐蚀性能 进行了初步探索,发现超声波可以提高合金的抗应力腐蚀性能,而对合金的硬度无影响。