Environmentally Assisted Cracking: Theory and Practice: Poster Session
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 6:00 PM
February 28, 2017
Room: Hall B1
Location: San Diego Convention Ctr

L-65: High Pressure Hydrogen Embrittlement of Fe-30Mn-0.2C-(1.5)Al High-Mn Steel: Seung-Yong Lee1; Han-Jin Kim2; Jin-Yoo Seo3; Jae-Hyeok Shim3; Joonho Lee2; Byoungchul Hwang1; 1Seoul National University of Science&Technology; 2Korea University; 3Korea Instiutute of Science and Technology
    Hydrogen energy society is rapidly coming, and environmental condition of materials for hydrogen system is getting worse. The commercial austenitic alloys used for hydrogen system have high production cost due to high content of expensive Ni. The tendency of hydrogen embrittlement of new austenitic alloys replacing Ni with Mn, C, N elements, therefore, has been actively studied over the last decades. There are austenitic stability, and stacking fault energy of materials as a criterion to estimate the hydrogen embrittlement of austenitic alloys. In this study, the tendency to hydrogen embrittlement of high-Mn steels was compared with other austenitic alloys in terms of stacking fault energy and deformation behavior as well as austenite stability. High-Mn steels with the chemical composition of Fe-30Mn-0.2C-(1.5Al) were pre-charged with hydrogen using high pressure-high temperature hydrogen reactor, followed by tensile testing in air. The microstructure and fracture surfaces were characterized by XRD, SEM, EBSD analysis.

L-66: The Characterization of Grain Boundary Precipitates in Aluminum-Magnesium Alloys at Mildly Elevated Temperatures: Sarah Fakler1; 1University of Virginia
    The presence of β phase (Al3Mg2) on the grain boundaries of Al-Mg alloys promotes intergranular stress corrosion cracking (IGSCC). The effect of composition (5456/5083) and temper (H116/ H131/solution heat treat and quenched (SHTQ)) on β morphology is investigated at constant ASTMG67 NAMLT values of 10, 24, and 40 mg/cm2. Tensile tests on electrochemically pre-charged samples enable SEM fractographic study of the morphology of β on the grain boundaries. These data are augmented by EBSD and selective etching techniques that enable analysis of the grain orientation dependence of β precipitation. This detailed characterization of the β morphology provides a means to evaluate the fidelity of the NAMLT value as a relevant proxy for describing IG-SCC susceptibility in engineering relevant Al-Mg alloys with different compositions and thermal treatments.

L-67: The Influence of Global Slip Behavior on Hydrogen Environment-Assisted Cracking in Monel K-500: Zachary Harris1; James Burns1; 1University of Virginia
    Lot-to-lot variations in metallurgical features and hydrogen-metal interactions have been shown to influence HEAC susceptibility in peak-aged Monel K-500. Evaluating the effect of global slip morphology on HEAC behavior in Monel K-500 will enable further understanding of observed lot-dependent behavior and provide insight into the general interaction between the bulk deformation behavior and the plasticity developed in the near-crack region during HEAC. The effect of global slip on HEAC metrics is evaluated through slow-rising stress intensity testing in both inert and aggressive (marine) environments. Systematically varied heat treatments are used to produce precipitate (γ’) sizes that result in distinct global slip behavior. High-fidelity characterization of localized plasticity/dislocation structures are conducted via high-resolution electron backscatter diffraction and transmission electron microscopy of specimens lifted from the crack wake using focused-ion beam techniques. Results are evaluated in the context of existing micromechanical models and the overarching contribution of localized plasticity is discussed.