Environmentally Assisted Cracking: Theory and Practice: Corrosion Fatigue and Cracking
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
Wednesday 8:30 AM
March 2, 2022
Room: 201D
Location: Anaheim Convention Center
Session Chair: Jenifer Locke, Ohio State University; Wenjun Cai, Virginia Tech
8:30 AM Invited
Correlating Crack Tip pH to Corrosion Fatigue Performance in Al Alloys: Jenifer Locke1; Katrina Catledge1; Gabriella Montiel1; Mary Cefaratti2; David Schrock1; Saba Esmaeely1; 1Ohio State University; 2Wittenberg University
For AA5xxx Al alloys, large cathodic polarizations have been shown to arrest both stress corrosion and corrosion fatigue cracking. Recent research suggests this arrest is due crack tip blunting. The current leading hypothesis for crack tip blunting in sensitized AA5xxx Al alloys loaded in aqueous chloride solutions and placed under cathodic polarization is increased cathodic reactions along the crack wake creating alkaline conditions that facilitate a breakdown of crack wake passivity and subsequent corrosion induced blunting of the crack tip. Research is ongoing to measure the crack tip pH of sensitized AA5xxx Al alloys under freely corroding conditions and several cathodic polarizations to produce results that either support or refute the alkaline corrosion crack tip blunting hypothesis. This talk will discuss this work as well as the methodology used for actively measuring crack tip pH while controlling K and measuring da/dN or da/dt depending on the loading spectrum applied.
9:05 AM
Effects of Atmospheric Corrosion on Corrosion Fatigue of AA7085-T7451: Investigating the Role of Surface Salts, Varied Humidity, and Temperature: Brandon Free1; Jason Niebuhr2; Nathan Houser2; Sarah Galyon Dorman2; Jenifer (Warner) Locke1; 1The Fontana Corrosion Center, The Ohio State University; 2SAFE Inc.
Corrosion fatigue (CF) of 7xxx series aluminum alloys has been studied extensively in standardized environments including pure water vapor and full immersion in aqueous solutions. Despite this, the effects of atmospheric environments consisting of salt deposits that yield surface electrolyte have not been widely examined. The objectives of this work are to quantify the effects of surface electrolyte droplets, humidity, and temperature on CF crack growth rates (da/dN) in AA7085-T7451. To date, testing has shown that da/dN measured in 0.06 M NaCl is similar to that measured with 50 - 300 μg/cm2 NaCl on the surface and exposed to 80% RH air. Additional testing has examined the hysteresis associated with changing humidity above and below the deliquescent point for NaCl, showing that humidity ramp rate and time of wetness/dryness may be important for understanding atmospheric CF. Testing is ongoing to examine the effect of temperatures between -40 to 25 C.
9:25 AM Invited
Designing Robust Aluminum Alloys and Structures Resistant to Simultaneous Surface Stress and Corrosion: Wenjun Cai1; 1Virginia Polytechnic Institute and State University
The increasing complexity and severity of service conditions in areas such as aerospace and marine industries, nuclear systems, microelectronics, batteries, and biomedical devices etc., imposes great challenge on the reliable performance of metal subjected to simultaneous surface stress and corrosion. However, the design of strong and corrosion-resistant alloys, especially those containing lightweight elements such as Al are challenged by the tradeoff between strength and corrosion resistance. Solute tends to have small equilibrium solubility limit in Al due to their relatively large negative enthalpy of mixing with Al. As a result, the formed precipitates strengthen the alloys, but compromises corrosion resistance due to their micro-galvanic coupling with the metal matrix. Two design strategies will be discussed to overcome this long-standing dilemma: by forming solid solution alloys and nanostructured multilayers. These studies provide insights for general design guidelines to engineer more robust, high-performance metals for use under harsh conditions.
10:00 AM Break
10:20 AM
Investigation of Fundamental Mechanical and Electrochemical Mechanism during the Tribocorrosion Process of Aluminum Using Experiments and Simulations: Kaiwen Wang1; Wenjun Cai1; 1Virginia Polytechnic Institute and State University
Aluminum and its alloys are excellent corrosion resistant materials due to its passivity and lightweight. However, the main threat to the integrity of Al based materials is tribocorrosion, during which corrosion and wear works synergistically to cause material degradation. In this work, fundamental mechanisms of tribocorrosion for Al are investigated on single crystal pure Al using both experimental methods and finite element (FE) simulations. Electrochemical properties were extrapolated from potential-dynamic measurements and mechanical properties from microindentation tests. Lattice rotation and dislocation density was characterized from crystallographic orientation mapping results. Based on the experimental inputs, a FE model was built to quantitatively analyze the wear process and the increase in corrosion rate due to depassivation, geometry effect, and wear-induced lattice rotation. The model is then verified by experimental results and proved capable of predicting the material loss due to tribocorrosion under different mechanical and chemical conditions.
10:40 AM
Investigating the Effect of Polarization on SCC Resistance of AA6111 and the Role of Crack Tip pH: Katrina Catledge1; Gabriella Montiel1; Saba Esmaeely2; Jenifer Locke1; 1The Ohio State University; 2DNV
AA6xxx Al-Mg-Si alloys are age-hardenable and resistant to stress corrosion cracking (SCC) compared to other age-hardened aluminum alloys. Their high strength-to-weight ratio makes them attractive for automotive applications in conjunction with steels and carbon fiber reinforced polymer (CFRP). In fracture mechanics-based experiments in 0.6 M NaCl, applied anodic polarization to simulate galvanic coupling with CFRP has been shown to severely reduce SCC resistance of AA6111-T8. When anodically polarized 100 mVSCE above the freely corroding potential (OCP), threshold stress intensity decreases to less than half that at OCP and Stage II crack growth rate increases. Testing under cathodic polarizations down to -1300 mVSCE does not appear to deleteriously affect SCC resistance. Efforts are ongoing to measure crack-tip pH in-situ and correlate effects of applied potential to SCC resistance. Part of this work is supported by the Department of Energy under award number DE-EE0007760 through a sub-award under PPG Industries, Inc.