Environmentally Assisted Cracking: Theory and Practice: Environmental Embrittlement, Fracture, and Fatigue
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee
Program Organizers: Bai Cui, University of Nebraska Lincoln; Raul Rebak, GE Global Research; Srujan Rokkam, Advanced Cooling Technologies, Inc.; Jenifer Locke, Ohio State University
Thursday 8:30 AM
February 27, 2020
Room: 2
Location: San Diego Convention Ctr
Session Chair: Jenifer Locke, The Ohio State University; Matthew Steiner, University of Cincinnati
8:30 AM Invited
Effects of Complex Atmospheric Environments on the Corrosion Fatigue of AA7085-T7451: Brandon Free1; Sarah Galyon Dorman2; Jason Niebuhr2; Jenifer Locke1; 1Fontana Corrosion Center, The Ohio State University; 2SAFE Inc.
Aluminum alloys used in aerospace applications can be exposed to complex atmospheric environments leading to corrosion fatigue (CF) when coupled with cyclic loading. The in-service environments encountered by these alloys are different than typical experimental CF environments and may lead to different per cycle crack growth rates (da/dN) and cracking at lower stress intensity ranges (ΔK). The objective of this work is to quantify and understand the effect of atmospheric exposure parameters such as relative humidity, temperature, ultraviolet light, ozone and fatigue loading frequency on CF of AA7085-T7451 with surface salt contamination. In support of this, da/dN is measured under constant ΔK while varying individual exposure parameters to isolate the effect of each parameter. Additional testing will vary multiple parameters simultaneously to observe synergistic and transient effects. The quantitative data produced in this study will further the understanding of CF in atmospheric environments.
9:10 AM
Microstructural Relationships to both Directional and Bulk Sensitization Responses in 5XXX Series Aluminum Alloys: Matthew Steiner1; Likun Sun1; 1University of Cincinnati
Despite the kinetics of sensitization behaving similarly for every grain boundary on a local scale, the bulk sensitization response of nominally identical 5XXX series aluminum alloy plates varies significantly within a given alloy-temper designation. As the starting microstructure and total rolling reduction are not specified by the temper, each material lot can possess a unique final microstructure. The extent of intergranular corrosion in sensitized materials is highly dependent on the exact geometric configuration of networked high-angle grain boundaries available for propagation. This leads to a large directional dependency in the degree of sensitization (as measured by corrosion) along different axes of anisotropic microstructures such as rolled plates. Utilizing adaptations of the Nitric Acid Mass Loss Test (NAMLT), used to assess bulk sensitization, we will present isolated directional inter-granular corrosion responses from different microstructures that help to establish ties between local boundary sensitivity, microstructural configuration, and the bulk NAMLT measurements.
9:30 AM
Tribocorrosion Resistance of Aluminum Alloys: The Effects of Scratching Frequency and Anodic Polarization: Jia Chen1; Wenjun Cai1; 1Virginia Polytechnic Institute and State University
Lightweight metals such as aluminum (Al) alloys have been widely used in various industries such as building and construction, transportation, packaging, and electrical devices due to its low density, high specific strength, good thermal and electrical conductivity, and recyclability. However, most commercial Al alloys are precipitation strengthened with compromised corrosion resistance resulting from localized galvanic coupling between the precipitates and Al matrix. In this work, we showed that, in contrary to precipitation strengthening, solid solution strengthening mechanism can be applied to simultaneously strengthen Al and improve their corrosion resistance, ultimately leading to enhanced tribocorrosion resistance. Specifically, the corrosion and tribocorrosion resistance of aluminum-manganese solid solutions were studied in simulated seawater. It was found that both the depassivation and repassivation kinetics are strongly affected by the scratching frequency and surface anodizing state during tribocorrosion.
9:50 AM Cancelled
Role of Chloride on the Fracture Behaviour of Micro-alloyed Steel in E20 Simulated Fuel Ethanol Environment: Olufunmilayo Joseph1; John Ade Ajayi2; Cleophas Loto1; Seetharaman Sivaprasad3; Himadri Bar3; 1Covenant University; 2Federal University of Technology, Akure; 3CSIR-National Metallurgical Laboratory
The need to fully comprehend the potential of pipelines in fuel ethanol applications has necessitated this study. The effect of chloride in E20 on fracture toughness and tearing resistance of micro-alloyed steel (MAS) was studied with three-point bend specimens. Monotonic J-integral tests were conducted in the presence and absence of chloride. Results show a decrease in fracture toughness of MAS in the presence of chloride, and a concurrent increase in its ductile tearing resistance. Fractographic examinations showed that chloride in E20 promoted quasi-cleavage fracture.
10:10 AM Break
10:30 AM
Microstructure Dependent Penetration and Recrystallization of Zinc by Gallium Based Liquid Metal Alloys: Justin Norkett1; Alec Chu2; Courtney Wiley2; Kit Manchette2; Victoria Miller1; 1University of Florida; 2North Carolina State University
Flexible electronic devices leveraging gallium liquid metal alloys as conductors are in development with the target of realizing such technologies as circuits and sensors immune to fatigue and antennas with on-the-fly reconfigurability. Despite the promise of these devices, the risks they pose to other metals at electrical interfaces and in their proximity is poorly understood. The process of liquid metal embrittlement (LME) has eluded explanation despite a century of study on the topic, in no small part due to the presence of several apparently distinct phenomena which can result from the action of a liquid metal on a solid metal substrate. This work utilizes modern electron microscopy techniques such as electron backscatter diffraction (EBSD) to characterize the effects quantifiable microstructural condition have on the grain boundary penetration of zinc by gallium based alloys.
10:50 AM
Environmental Assisted Deterioration Modeling of Large Glass Fiber Reinforced Polymer Composite Structures/Systems: Zhiye Li1; Michael Lepech1; 1Stanford University
The adoption of composites has been successful in manufacturing industries, and is rapidly expanding into civil infrastructure. One challenge to the broader adoption is a limited ability to model the synergistic effects of the combined physical/chemical processes of environmental exposure and mechanical loading. Unlike other building materials, long-term field-performance-data of polymer composites in construction applications does not exist. The first composite building system in the US is the facade of the San Francisco Museum of Modern Art (SFMOMA), completed in 2015. Since phenomenal-based service life models for composite building applications are not available, it is crucial to build multi-physical-based models in order to predict composite service life performance on a centennial time scale. This study begins to understand the thermo-chemical-mechanical degradation mechanisms of composite materials at multiple length scales. The framework is computationally modeled using COMSOLŪ using geometries and element properties that are provided by the manufacturer of SFMOMA facade.
11:10 AM
Stress Corrosion Cracking Assisted by Oxygen Embrittlement in Ti-6246: Yitong Shi1; Sudha Joseph1; Paraskevas Kontis2; Yanhong Chang2; Baptiste Gault2; David Dye1; 1Imperial College London; 2Max Planck Institute for Iron Research
In this work, two-point bend tests on Ti-6Al-2Sn-4Zr-6Mo were conducted at elevated temperatures and controlled environment to examine the susceptibility to hot salt stress corrosion cracking (HSSCC) by NaCl via adding a droplet of NaCl salt solution (0.1g /100ml) on the top of sample surface. The testing environment consisted of 0.2 bar O2 and 0.8 bar labelled water vapour D218O. Atom probe tomography study on the crack tip of sample tested under 450 ° C/ 650MPa showed a significant concentration of 18O in the alpha phase. The analysis by electron energy loss spectroscopy (EELS) equipped in TEM also revealed the high oxygen content around dislocations in beta phase. It was proposed that the oxygen atoms charging into the crack tip through corrosion reactions could give rise to enhanced plasticity ahead of crack tip and assist crack propagation.
11:30 AM Cancelled
Corrosion and Interstitial Triggered Grain Boundary Embrittlement of Al Alloys: Quanmei Guan1; Jing Sun1; Haisheng Wang1; Chengxiong Zou2; William Yi Wang2; Jijun Ma1; 1CRRC Tangshan Co.; 2Northwestern Polytechnical University
With the quick development of high-speed railway and the service of CRH for almost a decade, one of the greatest challenges is the maintenances of those trains in environmental conditions. It is critical to estimate the intergranular corrosion damage initiations and propagations. In this work, the corrosion of a nature-aged 6005A-T6 alloy was studied comprehensively. The typical features of the pits dominated by the distribution of precipitates include the peripheral dissolution of the Al matrix, channeling corrosion, intergranular attack, and large pits in the grains. ∑3[011](11 ̅1) coherent twin boundary (CTB) of FCC Al-X is utilized to reveal the interactions between interstitials (X = H, N and O) and CTB together with their embrittlement mechanism. The notable accumulation of bonding electrons of interstitial atoms occupying either T-site or O-site yields a dramatically reduction of Al-X and Al-Al bonding charge density and bonding strength, revealing the embrittlement mechanism of Al CTB.