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High-strength aerospace aluminum alloys, such as AA7075-T651, are susceptible to environmental assisted cracking (EAC) under the right combinations of stress, environment, and microstructure. EAC presents a serious risk to structures and equipment operated in corrosive conditions. Studies of EAC in aluminum alloys have highlighted the importance of both anodic dissolution and hydrogen embrittlement to EAC initiation and propagation.1–4 The EAC response of alloys under variable atmospheric conditions is of particular importance for assessing material performance for aerospace applications.
This work explores the effect of humidity and galvanic coupling on the environmental assisted crack initiation and growth rate of high-strength aluminum alloys under static load. Varied relative humidity and temperature cycles, based on relevant aircraft service environments, are used to identify factors leading to peak crack growth rate for a sodium chloride salt chemistry. The influence of dynamic environmental conditions versus constant environmental conditions are being evaluated. Aerospace materials are galvanically coupled to the aluminum substrate to quantify the effect on initiation time and growth rate. Spring-actuated double cantilever beam test systems with continuous sensor monitoring are employed in atmospheric environments with smooth-notch samples to produce estimates of time to crack nucleation, crack length, crack growth rate, and crack tip stress intensity. Simultaneous zero resistance ammeter measurement of the corrosion currents between galvanically coupled aerospace materials and the aluminum samples improves understanding of the relationships between atmospheric environment and the electrochemical processes leading to crack initiation and growth. Results demonstrate clear differences between wetting and drying processes, with peaks in galvanic corrosion current observed during drying and smaller peaks observed during wetting. Peaks in crack growth rate are observed at moderate relative humidity during drying processes.
Pyrolysis processes of post-consumer plastics are a promising chemical recycling route and a good alternative to disposal. Nevertheless, these processes are challenging for metallic materials since chlorine containing materials or biological components inside the feedstock can yield HCl and H2S, respectively, during cracking. In combination with high temperatures of the reactor zone metallic construction materials can be attacked by high-temperature corrosion.
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The spread of disbondment or corrosion from a scribe or holiday in a coating film, for which the terms rust creepage or undercutting are used in this paper is an important mechanism of coating degradation. The mechanism of rust creepage has been well studied by several authors who concur that the mechanism is driven by electrochemical reactions15. The reactions occurring at the discontinuity in the coating (scribe or holiday) involve an anodic reaction in which iron is dissolved. Adjacent to the anodic region, under the coating, a cathodic reaction occurs in which oxygen is reduced to hydroxyl ions.
With the rapid development of China's economy, energy and transportation industries have developed rapidly, and more and more oil and gas pipelines and urban rail transit have been built and put into use. Urban rail transportation systems, such as subways or light rail, generally use direct current traction and backflow through the rail. Because the track is not completely insulated from the earth, it is inevitable that some electric current will be discharged from the track to the earth to form stray electric current, which will cause interference to the surrounding metal components such as buried oil and gas pipelines.