Environmentally Assisted Cracking: Theory and Practice: Stress Corrosion Cracking II
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Bai Cui, University of Nebraska–Lincoln; Raul Rebak, GE Global Research; Sebastien Dryepondt, Oak Ridge National Laboratory; Srujan Rokkam, Advanced Cooling Technologies

Tuesday 2:00 PM
February 28, 2017
Room: 31A
Location: San Diego Convention Ctr

Session Chair: Sebastien Teysseyre, Idaho National Laboratory; Srujan Rokkam, Advanced Cooling Technologies

2:00 PM  Invited
Challenges and Recent Progress in High Fluence Irradiation Assisted Stress Corrosion Cracking: Sebastien Teysseyre1; 1Idaho National Laboratory
    Irradiation assisted stress corrosion cracking (IASCC) is a known issue in current nuclear reactors. In 60 year lifetime, reactor core internals may experience fluence levels up to 15 dpa for boiling water reactors (BWR) and 100+ dpa for pressurized water reactors (PWR). To support the safe operation of our fleet of reactors and maintain their economic viability, it is important to be able to predict any evolution of material behaviors as reactors age and, therefore, as fluence accumulated by reactor core components increases. This paper presents hypothesis on the effects of high fluence on IASCC susceptibility of stainless steels, the challenges faced to study those hypothesis and initial results will be presented.

2:40 PM  
3D Microstructural and Electrochemical Characterization of Galvanic Corrosion in Al7075-T651/316 Stainless Steel Couples: Sridhar Niverty1; Jason Williams1; Ilaksh Adlakha1; Scott Turnage1; Kiran Solanki1; Nikhilesh Chawla1; 1Arizona State University
    Dissimilar metal contact in aircraft and naval structures has proven to be a persistent problem as it facilitates galvanic corrosion. Despite decades of research in the area, a model that combines the microstructural and physical aspects to the electrochemical aspects of this complex phenomenon has yet to be developed. In this study, 3D X-ray microtomography has been employed to understand galvanic corrosion in Al7075-T651 coupled to a 316 Stainless Steel fastener in 3.5% NaCl. The effect of composition and distribution of inclusions on pitting characteristics and the evolution of corrosion damage with time will be discussed. Furthermore, the confluence of ex situ X-ray microtomography and potentiodynamic polarization methods has enabled us to comprehensively understand and predict pitting behavior in Al7075.

3:00 PM  
Direct Observations of Corrosion Cracking in a TEM: Claire Chisholm1; William Mook1; Steven Hayden2; Daniel Bufford1; Khalid Hattar1; Timothy Kucharski2; Michele Ostraat2; Katherine Jungjohann1; 1Sandia National Laboratories; 2Aramco Services Company
    Corrosion is a costly and ubiquitous challenge facing many industries, with trillions of dollars spent annually to repair and remediate corroded materials across sectors ranging from infrastructure and transportation to production and manufacturing. Prior to the current work, much of the research investigations into steel corrosion have been performed ex-situ. For steels containing a cementite phase, such studies show that corrosion-induced cracking occurs along cementite/ferrite boundaries, although inherent limitations to ex-situ observations still limit our understanding of the initial onset and development of the corrosion process. Here, we present our investigation of the corrosion cracking process in 1018 carbon steel using in-situ TEM liquid flow-cell corrosion techniques to directly investigate this failure phenomenon at the nanoscale.

3:20 PM  
Environmentally Assisted Cracking of Commercial Carbon Steels and Corrosion Resistant Alloys: Yugo Ashida1; Yuzo Daigo2; Katsuo Sugahara2; 1NHK International Corporation; 2Hitachi Metals MMC Superalloy, Ltd.
    Environmentally assisted cracking (EAC) occurs in commercial metals and alloys, including widely used carbon steels in automotive industry and stainless steels and nickel based super alloys in chemical industry. This review paper summarizes critical application problems and issues of EAC in each industry sector; current industrial level understanding on corrosion fatigue (CF), hydrogen induced cracking (HIC), and stress corrosion cracking (SCC); dominant factors affecting crack initiation and propagation; ongoing studies focusing on industrial approaches for improvement; trends and directions of future research and development.

3:40 PM Break

4:00 PM  
Assessing the Fracture Strength of Geological and Related Materials via an Atomistically Based J-integral: Reese Jones1; Louise Criscenti1; Jessica Rimsza1; 1Sandia National Laboratories
    Predicting fracture initiation and propagation in low-permeability geomaterials is a critical yet unsolved problem crucial to assessing shale caprocks for carbon sequestration and controlling fracturing for oil extraction. Experiments indicate that chemical reactions at fluid-geomaterial interfaces play a major role in subcritical crack growth. Engineering the subsurface fracture environment, however, has been hindered by a lack of understanding of the mechanisms relating chemical environment to mechanical outcome. We have developed an atomic-level understanding of the chemical-mechanical mechanisms that control subcritical cracks through coarse-graining reactive molecular simulations. With field estimators consistent with continuum conservation properties we are able to connect atomistic data to configurational-forces and fracture resistance. In order to trust this connection we have performed theoretical consistency tests and validation with experimental data. Although we have targeted geomaterials, this capability can have direct impact on other unsolved technological problems such as predicting the corrosion/embrittlement of metals and ceramics.

4:20 PM  
Sensitization Effects on Environmentally Assisted Cracking of Al-Mg Alloys: Mohsen Seifi1; Henry Holroyd1; Timothy Burnett2; John Lewandowski1; 1Case Western Reserve University; 2University of Manchester
    Environment induced cracking (EIC) in smooth tensile and fatigue pre-cracked test specimens of AA5083-H131 have been evaluated as a function of sensitization time up to 7,000 h, temperature (80C to 175C), and test environment. Slow strain rate testing of short-transverse smooth tensile samples, and pre-cracked S-T single edge notch specimens were conducted using a range of load point displacement rates. IGSCC was only promoted when straining was applied sufficiently slowly in a test environment capable of providing a local source of hydrogen. Exposure to an aqueous solution during sensitization at 80C, as opposed to dry air developed within an air-oven can influence EIC initiation. Detailed IGSCC evaluation using X-ray computed 3-D tomography and ultra-high-resolution electron microscopy has enabled mechanistic insights.

4:40 PM  
Structural and Mechanical Characterization of Corroded Region in 7075 Aluminum (Al) Alloy: Venkata Sathya Sai Renuka Vallabhaneni1; Tyler Stannard1; Ziguang Chen2; Shumin Li2; Florin Bobaru2; Nikhilesh Chawla1; 1Arizona State University; 2University of Nebraska-Lincoln
    In stress corrosion cracking, a determining factor for cracks propagating from corrosion sites and leading to failure is the structure of the damaged region near the corrosion surface. The evolution, microstructure, and mechanical properties of the corrosion layers have not been thoroughly investigated. We report on the 3D microstructure, composition, and mechanical properties in the corroded region of 7075 Al alloy corroded in 3.5wt.% NaCl. Visualization and quantification of the microstructure was done using X-ray tomography with a focus on the change in dimensions of the pits with increasing corrosion. Variation in tensile strength with amount of corrosion and its relation with microstructure was also studied. Compositional analysis in the cross-section of corroded region was done using EDS. To understand the variation of mechanical properties with distance from the corrosion surface, nanoindentation was performed. A peridynamic model was formulated to capture diffusion in the corrosion layer and will be discussed.

5:00 PM  
Environmentally Assisted Stress Corrosion Cracking of 5xxx Al Alloys in Atmospheric Environments: Patrick Steiner1; James Burns1; 1University of Virginia
    Intergranular stress corrosion cracking (IG-SCC) testing has typically been performed with specimens fully immersed in electrolytic solution due to experimental convenience. However, true atmospheric environments are often typified by salt-spray, rain, or a deliquesced thin-film electrolyte. These environments differ in the pertinent mass-transport distances and/or local ionic resistance influencing the cathodic/anodic reaction kinetics that control the crack tip hydrogen production. In this study the effect of atmospheric environments on the IG-SCC behavior of AA5083-H131 and AA5456-H116 tensile samples is studied using slow-rising displacement testing and high-fidelity monitoring of crack growth kinetics. These results are analyzed in the context of a coupled anodic dissolution and hydrogen-embrittlement mechanism, in which the observed reduction in the IG-SCC susceptibility of the atmospheric environments is cathodically limited. This would indicate a decrease in the dissolution at the crack tip, a less aggressive crack chemistry development, and subsequently lower levels of hydrogen production in atmospheric environments.