Atomistic Simulations of Carbon and Hydrogen Diffusion and Segregation in Alfa-Iron Deviant CSL Grain Boundaries
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.452
Atomistic Simulations of Carbon and Hydrogen Diffusion and Segregation in Alfa-Iron Deviant CSL Grain Boundaries Mohamed A. Hendy 1, Tarek M. Hatem 1, Jaafar A. El-Awady 2 1
Centre for Simulation Innovation and Advanced Manufacturing, the British University in Egypt, ElSherouk City, Cairo 11837, Egypt
2
Department of Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA
ABSTRACT
Polycrystalline materials’ mechanical properties and failure modes depend on many factors that include diffusion and segregation of different alloying elements and solutes as well as the structure of its grain boundaries (GBs). Segregated solute atoms to GB can alter the properties of steel alloys. Some of these elements lead to enhancing the strength of steel, on the other hand others can degrade the toughness of steel significantly. It is well known that carbon increases the cohesion at grain boundary. While the presence of hydrogen in steel have a drastic effects including blistering, flaking and embrittlement of steel. In practice during forming processes, the coincidence site lattice (CSL) GBs are experiencing deviations from their ideal configurations. Consequently, this will change the atomic structural integrity by superposition of sub-boundary dislocation networks on the ideal CSL interfaces. For this study, the ideal ∑3 (112) structure and its angular deviations in BCC iron within the range of Brandon criterion are studied comprehensively using molecular statics simulations. The GB and free surface segregation energies of carbon and hydrogen atoms will be quantified. RiceWang model is used to assess the strengthening/embrittlement impact variation over the deviation angles.
INTRODUCTION Solute segregation to grain boundaries (GBs) alters the mechanical properties of metallic alloys significantly [1,2]. Generally, the segregation of solute elements at GBs largely depends on the structure and character of these boundaries [3]. Some solutes increase the cohesive strength of the GBs while others have embrittlement effect [4]. Many studies have showed that Carbon segregation to GBs of α-iron increases the cohesive strength of these interfaces [5–7], while others have showed that carbon can increase slightly the embrittlement [8]. On the contrary, hydrogen segregation to GBs of α-iron always reduce the cohesive strength of the material’s interface causing premature intergranular fracture [9–13].
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Coherent twin boundaries (CTBs) have been shown to display good corrosion resistance in many engineering alloys [14]. It has been frequently observed that many GBs in real materials deviate from the ideal coincidence site lattice (CSL) symmetry plane [15–17]. Hence, The classification of a GB can be
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