Atomistic Simulations of Carbon and Hydrogen Diffusion and Segregation in Alfa-Iron Deviant CSL Grain Boundaries

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. Rice-Wang model is used to assess the strengthening/embrittlement impact variation over the deviation angles.