Understanding the Mechanisms Controlling Stress Corrosion Cracking Through High-resolution Characterization PDF Download

Author: Zhao Shen
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Remelisa P. Esteves
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Aluminum alloys are used on aerospace vehicles due to their high strength-to-weight ratio, formability and machinability. However, they become vulnerable to stress corrosion cracking (SCC) during their service life.SCC is primarily caused by the material’s stress condition, a suitable corrosive environment and material susceptibility. It is also influenced by a mixture of electrochemical, mechanical, and chemical factors. Due to the complexity of SCC, tools with better resolution and sensitivity are needed to better understand the impact and interaction of the contributing factors. A vast amount of research has been done to study SCC behavior, but the scale of characterization must be reduced to elucidate the key initiation mechanisms. In this work, it is shown that SCC initiation was detected early via micro-digital image correlation (micro-DIC) prior to the crack being discernible in microscopy images. The initial effort to monitor stress corrosion cracking in AA7075-T6 involved using a pixel resolution of 3.825 microns/pixel, frame rate of 10-15 min/image and an airbrush nozzle diameter of 0.3 mm for the speckle pattern, which led to the detection of crack initiation at 98% failure load. By using a pixel resolution that is 6 times smaller, a frame rate of up to 60 times less time per image, and an airbrush nozzle that is 2 times smaller, the first observation of strain concentration marking the eventual failure region of the AA7075-T6 sample was detected as early as 58% failure load. When the micro-DIC technique was applied to study SCC behavior in additively manufactured AlSi10Mg, the first observation of localized strain marking the eventual failure region of the sample was detected at 78% failure load. X-ray synchrotron tomography was used to qualitatively assess the hydrogen bubble and precipitate formation and to quantitatively assess the post initiation crack growth in AA7075-T651. With improved micro-DIC parameters and correlation with experimental outcomes from x-ray synchrotron tomography, multiple factors contributing to SCC can be assessed to better understand the mechanisms of SCC initiation. Correlations of material exposure time and load with SCC initiation can provide data for developing corrosion control strategies and new and improved alloys or heat treatment, as well as understanding SCC behavior in alloys made through unconventional means, such as additive manufacturing. The impact of this work lies in the life extension of alloys and greater reusability and fatigue life extension of aerospace vehicles.

Author: V S Raja
Publisher: Elsevier
ISBN: 0857093762
Category : Technology & Engineering
Languages : en
Pages : 817

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The problem of stress corrosion cracking (SCC), which causes sudden failure of metals and other materials subjected to stress in corrosive environment(s), has a significant impact on a number of sectors including the oil and gas industries and nuclear power production. Stress corrosion cracking reviews the fundamentals of the phenomenon as well as examining stress corrosion behaviour in specific materials and particular industries.The book is divided into four parts. Part one covers the mechanisms of SCC and hydrogen embrittlement, while the focus of part two is on methods of testing for SCC in metals. Chapters in part three each review the phenomenon with reference to a specific material, with a variety of metals, alloys and composites discussed, including steels, titanium alloys and polymer composites. In part four, the effect of SCC in various industries is examined, with chapters covering subjects such as aerospace engineering, nuclear reactors, utilities and pipelines.With its distinguished editors and international team of contributors, Stress corrosion cracking is an essential reference for engineers and designers working with metals, alloys and polymers, and will be an invaluable tool for any industries in which metallic components are exposed to tension, corrosive environments at ambient and high temperatures. - Examines the mechanisms of stress corrosion cracking (SCC) presenting recognising testing methods and materials resistant to SCC - Assesses the effect of SCC on particular metals featuring steel, stainless steel, nickel-based alloys, magnesium alloys, copper-based alloys and welds in steels - Reviews the monitoring and management of SCC and the affect of SCC in different industries such as petrochemical and aerospace

Author: Martina Meisnar
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Karen Kruska
Publisher:
ISBN:
Category : Atom-probe field ion microscopy
Languages : en
Pages : 196

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Author: John H. Jackson
Publisher: Springer
ISBN: 3030046397
Category : Technology & Engineering
Languages : en
Pages : 2460

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This two-volume set represents a collection of papers presented at the 18th International Conference on Environmental Degradation of Materials in Nuclear Power Systems – Water Reactors. The purpose of this conference series is to foster an exchange of ideas about problems and their remedies in water-cooled nuclear power plants of today and the future. Contributions cover problems facing nickel-based alloys, stainless steels, pressure vessel and piping steels, zirconium alloys, and other alloys in water environments of relevance. Components covered include pressure boundary components, reactor vessels and internals, steam generators, fuel cladding, irradiated components, fuel storage containers, and balance of plant components and systems.

Author: Jie Gao
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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"Stress corrosion cracking (SCC) is a type of subcritical cracking of materials that occurs when a SCC susceptible material is simultaneously stressed in tension (applied or residual) and exposed to a specific corrosive environment. Failure of materials due to SCC could occur at stress levels much lower than the allowable service stress, causing catastrophic consequences. Decades of efforts to investigate the SCC phenomena have established the general behaviors of different materials during SCC and it is widely accepted that a susceptible material, tensile stress, and a specific corrosive environment are the prerequisites for the occurrence of SCC. However, the fundamental mechanisms behind the apparent SCC behaviors remain unclear mainly due to contradictory experimental data from different researchers, the intrinsic difficulties associated with material characterization within the restricted geometry of cracks, and the complexity of the interactions between different chemical species. In this thesis, attention is focused on a single material system, AA5083 aluminum alloy, where the SCC can be made to happen quickly so that the effects of various aspects on SCC can be examined within reasonable amounts of time, for the purpose of mechanistic study. To clear the controversies about the actual SCC behaviors and to better understand the basic mechanisms of SCC, all of the three prerequisites of SCC, i.e. susceptible material, tensile stress, and corrosive environment, have been carefully examined using various materials characterization techniques. For the metallurgical aspect (susceptible material), AA5083 aluminum alloy (Al-4.4Mg-0.7Mg-0.15Cr) has been intentionally annealed at 175 °C, a process called sensitization, for a series of progressively longer treatment times. The SCC behaviors, microstructures, mechanical properties, and electrochemical properties of these differently heat treated AA5083 specimens have been characterized. It is found that the SCC incubation time decreases for longer sensitization time while the SCC initial crack growth rate increases as sensitization time becomes longer. This phenomenon is explained as a result of the development of continuous films of anodic intermetallic, Mg2Al3, known as [beta]-phase, on the grain boundaries as sensitization time increases, based on the microstructural, electrochemical, and mechanical characterizations. For the environmental aspect (corrosive environment), the SCC behaviors, as well as microstructures, of AA5083 sensitized for both 120 and 240 hours have been examined in sodium chloride (NaCl) solutions with different concentrations and pH. It has been found that both higher NaCl concentration and lower pH values lead to shorter incubation time, higher initial crack growth rate and higher total crack growth, and the SCC behaviors of the specimens that have been sensitized for 240 hours are more sensitive to environmental factors, compared with their counterparts with 120 hours sensitization condition. The fractographic analysis demonstrates the cracking mechanism is independent of the environmental factors and is still anodic dissolution based intergranular separation. The interactions between mechanical driving force (stress intensity) and chemical driving force (NaCl concentration) are also discovered. For the mechanical aspect (tensile stress), the SCC behaviors of sensitized AA5083 with different initially applied stress intensity levels have been investigated. It is found that the incubation time is a chemical process while the initial crack growth rate and total crack propagation are determined by both mechanical and chemical driving forces. The interactions between mechanical and chemical driving forces are described as a process that is dominated by chemical driving force and only assisted by mechanical driving force. Additionally, the crack mechanism is found to be anodic dissolution as well, for all different starting stress intensities. All of the above experimental efforts indicate that anodic dissolution is the dominant mechanism for SCC in sensitized AA5083 alloy."--Leaves v-vii

Author: C. J. Slunder
Publisher:
ISBN:
Category : Steel, High strength
Languages : en
Pages : 50

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Author: Ellis E. Fletcher
Publisher:
ISBN:
Category : Metals
Languages : en
Pages : 28

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High-strength steels are susceptible to delayed cracking under suitable conditions. Frequently such a brittle failure occurs at a stress that is only a fraction of the nominal yield strength. Considerable controversy exists over whether such failures result from two separate and distinct phenomena or whether there is but one mechanism called by two different names. Stress-corrosion cracking is the process in which a crack propagates, at least partially, by the stress induced corrosion of a susceptible metal at the advancing tip of the stress-corrosion crack. There is considerable evidence that this cracking results from the electrtrochemical corrosion of a metal subjected to tensile stresses, either residual or externally applied. Hydrogen-stress cracking is cracking which occurs as the result of hydrogen in the metal lattice in combination with tensile stresses. Hydrogen-stress cracking cannot occur if hydrogen is prevented from entering the steel, or if hydrogen that has entered during processing or service is removed before permanent damage has occurred. It is generally agreed that corrosion plays no part in the actual fracture mechanism. This report was prepared to point out wherein the two fracture mechanisms under consideration are similar and wherein they differ. From the evidence available today, the present authors have concluded that there are two distinct mechansims of delayed failure. (Author).

Author: Julius J. Harwood
Publisher:
ISBN:
Category : Stainless steel
Languages : en
Pages : 8

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The purpose of this discussion is to assess the state of our understanding concerning the factors and mechanism(s) which determine and control the susceptibility to stress-corrosion cracking of the austenitic stainless steels. The growing importance of this problem has led to a considerable amount of research, both in this country and abroad, aimed at delineating more specifically the environmental, compositional, and structural conditions involved and at elucidating the underlying mechanism for the cracking phenomenon. As a result of this research effort, a number of mechanisms have been proposed, but all appear to contain certain deficiencies in explaining certain of the characteristic features of the stress-corrosion cracking process; that is to say, unequivocal arguments cannot be presented in behalf of any of the proposed mechanisms. Possibly more to the point is the fact that few of the currently debated mechanisms have yielded critical clues which could lead to compositional or structural modifications of commercial materials to reduce or prevent the incidence of cracking. It is encouraging to note, however, that the more recent experimental evidence is developing a basis whereby critical type of experiments can be designed to differentiate clearly the mode of damage.