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Collaborating Authors
Zhu, Yakun
Predicting Corrosion Fatigue Behavior Using a Bayesian Network That Integrates Microstructure, Electrochemistry and Fracture Mechanics
Taylor, Christopher (DNV GL) | Bland, Leslie (Ohio State University) | Frankel, Gerald (Ohio State University) | Locke, Jenifer (Ohio State University) | Zhu, Yakun (Ohio State University) | Garofano, Jacquelynn (United Technologies Research Center (UTRC)) | Smith, Kenneth (United Technologies Research Center (UTRC))
ABSTRACT The localized corrosion and cracking of lightweight alloys is a complex, non-linear and stochastic function of the variables concerning materials composition, thermal and mechanical processing, and environmental parameters such as solution chemistry, temperature, electrochemical potential and mechanical stress. Integrating these variables into a coherent model poses a ‘grand challenge’ in corrosion science and engineering. In this conference paper, a Bayesian network approach that integrates these variables into a single model is presented based upon pre-existing models taken from the literature as well as data-sets that provide electrochemical ‘fingerprints’ for the cathodic and anodic behavior of intermetallic particles. Laboratory analyses of the microstructure of 7075 and 2070 alloys and the electrochemical properties of the intermetallic properties provide the inputs for the Bayesian network model. Corrosion fatigue experiments combined with a literature survey to determine statistically distributed crack growth rates are used to generate Paris laws that are incorporated into the model for determination of the pit-to-crack transitions and estimate the overall number of cycles to failure. INTRODUCTION The high strength of aluminium alloys is achieved through addition of alloying elements that promote precipitation hardening. However, these precipitates reduce resistance to localized corrosion and corrosion fatigue due to the microgalvanic interactions that occur when the intermetallic particles have corrosion potentials that differ from the solid solution aluminium matrix. A considerable body of work has been devoted to characterizing these intermetallic particles from the standpoint of size, clustering, orientation, and electrochemical activity. Intermetallic particles may be either anodic or cathodic to the matrix depending on their composition and their local environment. Both types of particles may initiate localized corrosion: anodic particles may dissolve creating occluded spaces of aggressive solution chemistry that can catalyse further dissolution of the surrounding Al matrix; and cathodic particles can catalyse corrosion by generating counter currents and also locally alkaline pH that can dissolve the surrounding Al matrix through the formation of [Al(OH)4] ions and similar oligomeric species.
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
- Data Science & Engineering Analytics > Information Management and Systems > Artificial intelligence (1.00)
Experimental Validation of Long Term Thermal Exposure Sensitization of AA5xxx Alloys
Zhu, Yakun (Department of Metallurgical Engineering, University of Utah) | Kar, Soumya (Department of Metallurgical Engineering, University of Utah) | Free, Michael L. (Department of Metallurgical Engineering, University of Utah) | Cullen, David A. (Materials Science & Technology Division, Oak Ridge National Laboratory) | Allard, Lawrence F. (Materials Science & Technology Division, Oak Ridge National Laboratory)
ABSTRACT: In the present work, ß-phase formation along grain boundaries has been evaluated by scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) analysis methods. The thickness of ß-phase along grain boundaries, measured by STEM for a 1-year thermally treated sample, was estimated to be 15 - 20 nm. Etching effects of phosphoric acid solution and ammonium persulfate solution on the Al matrix are discussed. The effect of ASTM G67 nitric acid attack on different surfaces was investigated. Mass loss data was collected for several AA5xxx alloys using long-term (~ 12 months), constant temperature (40 to 70°C) exposure tests. Other samples were treated in thermal exposure furnaces with cyclic temperatures (40 to 45°C and 50 to 70°C) to represent the heating cycles in service conditions. INTRODUCTION Although the presence of different intermetallic precipitates in the matrix of 5083 alloys improves mechanical properties1,2, one type of precipitate, Al3Mg2, or ß-phase, compromises corrosion resistance3, 4. The ß-phase has a corrosion potential of around -1.29V (saturated calomel electrode) which makes it typically more active than the AA5083 (UNS A95083) Al matrix, which has a corrosion potential of -0.73V (saturated calomel electrode). Thus the ß-phase is preferentially attacked by corrosive environments4, 5, 6. The ß-phase is usually associated with intergranular corrosion (IGC) and stress corrosion cracking (SCC) 6, 7. ß-phase formation reduces the service life and quality of aluminum parts. Considerable research has been conducted to understand the mechanisms of ß-phase-related corrosion phenomena4, 5, 6, 7, 8, 9, 10, 11, 12. Samples for SEM imaging were mounted in epoxy resin, polished to 1 ~ 0.02 micron, and then etched using a phosphoric acid solution (10 vol. % or 1.72 M phosphoric acid) to make the ß-phase visible as etch trenches in secondary electron images of the cross-section samples.
- Materials > Chemicals > Commodity Chemicals (1.00)
- Government > Regional Government > North America Government > United States Government (1.00)
- Health, Safety, Environment & Sustainability (0.67)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (0.48)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (0.47)