Environmentally Assisted Cracking: Theory and Practice: Corrosion and Fracture in Harsh Environments
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 2:00 PM
March 18, 2021
Room: RM 18
Location: TMS2021 Virtual
Session Chair: Nikhilesh Chawla, Purdue University; Brendy Troconis , University of Texas at San Antonio
2:00 PM Invited
Spectroelectrochemical Evaluation of Carbon Steel in Slightly Sour Environments Under the Presence of H2S/CO2 and Triazine-Based H2S Scavenger: Vinicio Ynciarte1; Leonardo Caseres2; James Dante2; Brendy Rincon Troconis1; 1University of Texas at San Antonio; 2Southwest Research Institute
Injecting H2S scavenger is a common practice to reduce H2S in the oil and gas industry. Nevertheless, failures in the form of SCC of steel pipes in the presence of MEA-triazine have been reported. The effects of this chemistry on the corrosion and cracking mechanism of carbon steel is unknown. Therefore, in this work, a spectroelectrochemical evaluation based on in-situ Raman spectroscopy, in-situ surface enhanced Raman spectroscopy, electrochemical techniques and SSRT was utilized. This methodology was selected to identify: the chemical species present in the test solution prior to and following the scavenging process, measure specific adsorption of amine by-products on the steel, changes in the surface film composition, assess the electrochemical behavior, and evaluate SCC susceptibility. Based on literature related to corrosion in bicarbonate containing environments and the results of this work, it is suggested that SCC is governed by a possible transition from passive to active kinetics.
2:40 PM
A Multiphysics Model of Synergistic Environmental Exposure Assisted Damage of Composite Using Homogenization-based Degradation Variables: Zhiye Li1; Michael Lepech1; 1Stanford University
Glass Fiber-reinforced polymer composites (GFRPs) are made by combining polymer with reinforcement glass fiber yarns to produce lightweight yet strong materials. This study is to build a physics-based model to predict the synergistic effect of environmental exposure to damage of the composite. Based on the authors’ previous UV/ moisture exposure experiment-computational study, this extended study couples degradation induced material weakening to the continuum damage model. Results of this study indicate that the synergistic effect of combined UV and moisture exposure on composite material degradation is more severe than simple linear superposition of each exposure’s damage. Comparisons and analysis of UV and moisture exposure degradation mechanisms indicate that these environmental exposures caused material degradation by weakening the polymer matrix, along with weakening the interface between the polymer matrix and fiber reinforcing yarns. Moreover, interface degradation is more critical than the former one.
3:00 PM
Combined Ab-initio and Experimental Study of Hydrogen Sorption in Dual Phase Steels: Saurabh Sagar1; Vera Popovich1; Pascal Kömmelt2; Poulumi Dey1; 1Delft University of Technology; 2Research and Development, Forming Technology, Tata Steel Ijmuiden BV
Controlling the detrimental effect of hydrogen on the mechanical behaviour of AHSS is decisive for their application. A combined ab-initio- experimental approach was used to study the hydrogen sorption in two different DP800 steel grades using cyclic voltammetry and potentiostatic oxidation. Under the same charging conditions, diffusible hydrogen concentration was found to be higher in the vanadium grade as compared to the titanium grade. Scanning Electron Microscope characterisation revealed a more compact layer of oxide on the vanadium grade which contributed to more hydrogen absorption on the surface. Density Functional Theory calculations were performed to determine the trapping strength of precipitates of titanium and vanadium. Off-stoichiometric vanadium carbide was found to be the strongest trap, with carbon vacancies in the bulk of precipitates being favourable hydrogen trapping sites. Comparison of the DFT results with experiments suggested that the absorbed hydrogen could not reach the precipitates where it could get trapped.
3:20 PM
Fatigue Crack Propagation in AA7085-T7451 Exposed to Complex Atmospheric Environments: Brandon Free1; Sarah Galyon Dorman2; Jason Niebuhr2; Jenifer Locke1; 1The Ohio State Uniersity; 2SAFE Inc.
AA7085-T7451 is used in complex aerospace environments of varied temperature, humidity, and ozone level while also being exposed to surface salt deposits that can form electrolyte droplets. The effect of these atmospheric environments on corrosion fatigue (CF) is not well understood. The objective of this work is to quantify the effect of these environments on CF crack growth rates (da/dN) when surface salt deposits are present and to compare against traditional environments. Testing to date has shown similar da/dN over a range of fatigue loading frequencies when comparing full immersion in 0.06M NaCl to 80% RH with 300 μg/cm2 of deposited NaCl. During a wet-dry cycling, testing shows a sudden increase in da/dN when RH is increased past the deliquescent point. This acceleration persists unless dried to an RH well below the deliquescent point. Overall, this work will lead to a better quantitative understanding of corrosion fatigue in atmospheric environments.This material is based on research sponsored by the USAFA and The Ohio State University under agreement number FA7000-18-2-0001. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. The opinions, findings, views, conclusions or recommendations contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied of the USAFA and the U.S. Government.
3:40 PM
The Effect of Applied Potential and Loading Rate on the Hydrogen Environment-assisted Cracking Behavior of AA7075-T6511: Zachary Harris1; Alen Korjenic1; John Scully1; James Burns1; 1University of Virginia
The effect of applied potential and loading rate on the hydrogen environment-assisted cracking behavior of the legacy aerospace aluminum alloy AA7075-T6511 was assessed using a slow-rising stress intensity (K) testing framework. Fracture mechanics experiments were performed in 0.6 M NaCl at applied potentials ranging from -1300 to -750 mVSCE (vs. saturated calomel electrode) and fixed loading rates (dK/dt) ranging from 0 to 2.0 MPa√m/hr. Results demonstrate that AA7075-T6511 exhibits similar crack growth rates and threshold stress intensities for potentials more negative than -1000 mVSCE and more positive than -900 mVSCE. However, between -900 and -1000 mVSCE, a clear reduction in HEAC susceptibility was observed. Interestingly, unlike other aluminum alloys, HEAC kinetics were found to relatively insensitive to the applied dK/dt in both 0.6 M and 1.0 M NaCl across the tested applied potential range. The mechanistic basis for these observations is assessed and the implications on HEAC mitigation strategies discussed.
4:00 PM
Phase-field Modeling of Galvanic Corrosion in Magnesium-Aluminum Joints: Kubra Karayagiz1; Adam Powell1; Qingli Ding1; Brajendra Mishra1; 1Worcester Polytechnic Institute
Aluminum and magnesium alloys are shown to be amongst the best candidate materials for light-weighting purposes due to their superior properties. However, the joining of Al and Mg is challenging due to galvanic corrosion, a common issue in dissimilar metal joints. A quaternary phase-field model to study the galvanic corrosion in Al-Mg joints is presented in this work. The model accounts for the conservation of charge, transport of ions in the electrolyte, the electrochemical reactions at the metal-electrolyte interface, and the formation of hydroxide phases on the metal surface. Two-dimensional simulations are performed to predict the corrosion microstructure, corrosion rate, and galvanic current density in diffusion bonded Al-Mg couples immersed in an electrolyte solution. Galvanic corrosion experiments are conducted for validation purposes. The corrosion model formulation presented here is intended for later use with micro-galvanic corrosion between pure metal and intermetallic phases in complex friction stir welded magnesium-aluminum joint microstructures.
4:20 PM
Understanding Pitting Corrosion in a High-performance Aluminum Alloy by Four-dimensional (4D) X-ray Microtomography: Daniel Sinclair1; Sridhar Niverty1; Nikhilesh Chawla1; 1Purdue University
Aluminum alloys are commonly used in aeronautical and energy applications due to their high strength-to-weight ratio and low cost. Pitting corrosion is a major detriment to the service lifetimes of aluminum alloys in severe environments. Electrochemical analysis and two-dimensional (2D) characterization methods have previously produced limited mechanistic descriptions of corrosion processes. These methods do not, however, do not produce an in-depth image of localized corrosion mechanisms due to their destructive nature and limited regions of interest. In this study, we have used lab-scale x-ray microtomography to non-destructively quantify and characterize pit growth in three dimensions in a cold-rolled AA7075-T651 alloy. Renderings of sample volumes were used to correlate important trends in mechanisms of pitting with local microstructural features driven by sample processing. A more unified understanding of how inclusion particles and corrosion product contribute to stable pit growth was achieved and will be discussed.
4:40 PM
Formation of Ni-O-H-S Surface Phases on Cathodically Charged Ni: Lai Jiang1; Stanislav Verkhoturov1; Emile Schweikert1; Michael Demkowicz1; 1Texas A&M University
We investigate the formation of surface phases on nickel (Ni) during cathodic charging in 1M H2SO4 solution. We characterize these new phases using a wide range of characterization techniques, including XRD, EBSD, Kelvin Probe Force Microscopy (KPFM), EDS, and SIMS. We confirmed that these phases are complexes that rich in Ni, O, H and S, but free of C. In steady-state, the phases have distinct crystal structures, and are aggregated into surface filamentary shape with a thickness of ~200nm and covered approximately 30% of the Ni surface. They appear to be thermodynamically stable in air but are also easily removed by ultrasonication. Most importantly, the surface electrochemical potentials of these phases are cathodic with respect to the surrounding Ni surface by ~120mV. These findings stand to advance understanding of the catalytic activity of Ni cathodes, H uptake and embrittlement in Ni, and the onset of localized corrosion during cathodic charging.