Environmentally Assisted Cracking: Theory and Practice: Corrosion and Degradation in Harsh Environments I
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 2:00 PM
March 2, 2022
Room: 201D
Location: Anaheim Convention Center

Session Chair: C. Cem Tasan, Massachusetts Institute of Technology; Yanfei Gao, University of Tennessee

2:00 PM  Invited
Hydrogen Effects in Metals: New Tools, New Insights: C. Tasan1; Jinwoo Kim1; Haoxue Yan1; 1Massachusetts Institute of Technology
    Hydrogen can easily diffuse in metals, significantly altering elastic and plastic properties. These effects have long standing engineering consequences (e.g., hydrogen embrittlement susceptibility in alloys), and still draw significant attention due to present energy-related challenges and potential transition to hydrogen economy. From a physical perspective, the underlying mechanisms of these effects are interesting. Depending on the metal, and its microstructure, similar levels of hydrogen can trigger different micro-mechanisms, the nature of some of which are highly-debated. In multi-phase metals, multiple mechanisms can be activated simultaneously, further increasing the complexity. In this talk, I will be introducing several new in-situ characterization techniques developed in-house that shed more light on the nature of these mechanisms. These insights provide new guidelines for the design of new alloys, as will be discussed.

2:35 PM  
Alloy and Process Modification for Reduced Hydrogen Sensitivity of High Hardness Steel: William Williams1; Shiraz Mujahid1; Shane Brauer1; Haley Doude1; Kevin Doherty2; Daniel Field2; Krista Limmer2; Hongjoo Rhee1; 1Mississippi State University; 2CCDC Army Research Laboratory
    High hardness steels are highly susceptible to hydrogen embrittlement. One mitigation strategy includes the introduction of strong hydrogen traps to arrest diffusible hydrogen. An investigation was made into implementation of strong hydrogen traps via alloying and process modification to produce a high hardness steel with a reduced sensitivity to hydrogen embrittlement. The material was directly compared to a baseline alloy free of traps. Both materials were evaluated in terms of hardness, energy absorption, and hydrogen sensitivity. Subsize tensile samples were electrochemically charged with hydrogen and slow strain rate testing was performed. The comparison of the modified alloy to the baseline demonstrated the effect of microalloying and tempering times on reducing the sensitivity of the material to hydrogen embrittlement.

2:55 PM  
NOW ON-DEMAND ONLY – Role of Accumulated Plastic Strain on Grain Boundary Corrosion of Steel: Amir Abdelmawla1; Kaustubh Kulkarni1; Ashraf Bastawros1; 1Iowa State University
    Steel structures may experience localized plastic strains, arising from wide range of service anomalies. Regions of accumulated plastic strain are more prone to accelerated stress corrosion cracking. Here, we systematically analyzed the intergranular corrosion (IGC) at potentials of active dissolution in moderately alkaline carbonate-bicarbonate solutions and under pre-accumulated plastic strain ranging from 0-2.5%. We report the strain-dependent morphological evolution during the initial stage of IGC of X70 steel in sodium bicarbonate solution, in the potential range of high SCC susceptibility. At potentials in the range of SCC susceptibility, IGC creates triangular wedges of porous corrosion products centered at grain boundary triple junctions. The wedges shapes and the total integrated charge from the polarization curves where greatly affected and correlated with the level of the accumulated plastic strains. These findings provide a plausible link of a coupled chemical-mechanical mechanisms responsible for the accelerated SCC in regions of plastically deformed structures.

3:15 PM  
NOW ON-DEMAND ONLY – Mechanisms of Mitigating Chloride-induced Stress Corrosion Cracking of Austenitic Steels by Laser Shock Peening: Yongchul Yoo1; Xueliang Yan1; Fei Wang1; Qiuchi Zhu1; Yongfeng Lu1; Bai Cui1; 1University of Nebraska-Lincoln
    This manuscript investigates the effect of laser shock peening (LSP) on the chloride-induced stress corrosion cracking (SCC) of 304 austenitic steels. LSP can induce a high compressive residual stress and plastic deformation. Constant-load SCC tests in a 42% MgCl2 solution suggested that LSP can retard the crack initiation and slow the crack growth. LSP-treated subsurface layers experience ductile fracture while the central regions exhibit intergranular SCC. The LSP-induced deformation structures may reduce slip-dissolution by impeding dislocation slips, while the LSP-induced compressive residual stress can lessen the stress intensity factor of crack tips and decrease the local stress for film rupture.

3:35 PM Break

3:55 PM  Invited
On the Critical Role of Localized Oxidation Processes in High Temperature Failures under Cyclic Thermomechanical Loading Conditions: Yanfei Gao1; 1University of Tennessee-Knoxville
    Alloy materials subjected to cyclic thermomechanical conditions are oftentimes analyzed from damage mechanics approaches, which however bear no direction condition to the detailed failure processes. Motivated by the oxidation finger formation under isothermal and cyclic oxidation conditions, this work proposes that localized oxidation processes, together with the stress generation from concomitant oxidation-creep-diffusion processes, dictate the failure initiation in a wide range of experimental observations. Oxidation fingers or pegs under cyclic thermomechanical loading conditions can extend into the superalloy substrate or expand laterally, contingent on the extent of plastic yield in these geometric defects. It is found that an extended holding at high temperature promotes the development of a large tensile stress in the superalloy substrate and thus stabilizes/suppresses the growth of such defects. Insights from these theoretical studies will be compared to some recent experiments for turbine materials.

4:30 PM  
Corrosion and Mechanical Characterization of Friction-stir Welded Joints between Aluminum and Magnesium Alloys: Qingli Ding1; Kübra Karayagiz1; Brajendra Mishra1; Adam C Powell1; Donovan Leonard2; 1Worcester Polytechnic Institute; 2Oak Ridge National Laboratory
    Cyclic Corrosion Test (CCT) is now considered a more reliable and realistic test for automotive applications than the traditional steady-exposure methods, such as the salt spray test. Several automotive companies have established their own testing protocol for CCT. In this project, under certain uncoated conditions that represent the worst-case scenario for coupled bimetallic, following the SAE J2334 standards, we are conducting the CCT method on the next generation Friction Stir Welding Magnesium-Aluminum Vehicle Joints. For certain applications, such as the Stellantis-Magna ultra-light door, subassemblies using these alloys are up to 50% lighter than those using conventional steel-based alloys. The electrochemical analyses of corrosion rate by Open Circuit Potential (OCP) and Linear Polarization Resistance (LPR) have been performed. Scanning Electron Microscopy (SEM) characterization of the surface change during corrosion and the mechanical properties including Microindentation Hardness Mapping and Lap Shear Strength have been conducted.

4:50 PM  
Modeling of Corrosion and Mechanical Failure in Friction Stir Welded Magnesium-aluminum Vehicle Joints: Kubra Karayagiz1; Adam Powell1; Qingli Ding1; Donovan Leonard2; Piyush Upadhyay3; Brajendra Mishra1; 1Worcester Polytechnic Institute; 2Oak Ridge National Laboratory; 3Pacific Northwest National Laboratory
    Computational modeling tools are presented to study the various types of corrosion and mechanical failure in friction stir welded Al-Mg vehicle joints. First, a phase-field model to study corrosion in Al-Mg joints is developed. 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. Results for models of pitting corrosion and galvanic oxidation show qualitative agreement with experiments. Next, a finite element model is developed to study the effect of corrosion on joint performance. Mechanical properties of different regions (e.g., heat affected zone, stir region) are determined based on nanoindentation experiments, while the geometry of the mechanical hooks is extracted from the scanning electron microscopy images. Experiments are conducted for validation purposes.