Atomic diffusion in the Fe [0 0 1] ∑ = 5 (3 1 0) and (2 1 0) symmetric tilt grain boundary

Both the formation and diffusion activation energies of single vacancy migrating intra-layer and inter-layer near the Fe [0 0 1] Σ = 5 (3 1 0) and (2 1 0) symmetric tilt grain boundaries have been calculated by using the MAEAM and a MD method. From energy minimization, the vacancy concentration in the second layer is higher than the one in the other layers for both (3 1 0) and (2 1 0) STGBs. By the diffusion activation energies of the vacancies migrating intra-layer and inter-layer, the vacancies located from the first to the eighth layers of (3 1 0) STGB as well as the ones located from the first to the tenth layers of (2 1 0) STGB are favorably migrated to the second layer. Thus there is a vacancy aggregation tendency to the second layer near the grain boundary. For the vacancy migrating intra-layer and inter-layer, the influences of the grain boundary are respectively as far as to the fifth and eighth layers for (3 1 0) STGB as well as to the sixth and tenth layers for (2 1 0) STGB.     

Effect of Cr precipitates and He bubbles on the strength of 〈1 1 0〉 tilt grain boundaries in BCC Fe: An atomistic study

Molecular static simulations were carried out to study the fracture process of different 〈1 1 0〉 tilt grain boundaries (Σ19{3 3 1}, Σ9{2 2 1}, Σ3{1 1 1}, Σ3{1 1 2}, Σ11{1 1 3}, Σ9{1 1 4}). The main goal of this work was to investigate variation of the deformation mechanism and fracture stress in the presence of Cr precipitates, voids and He bubbles at the core of the grain boundaries (GBs). The corresponding deformation process was characterized in terms of stress–strain relationship and deformation mechanisms were inspected by visualization tools. Based on the obtained stress–strain curves, the studied GBs can be subdivided into two types, those that exhibit extensive slip and those that do not show slip at all. The presence of Cr precipitates at the GB core increases critical shear stress necessary to initiate the slip, and nucleation of a crack was regularly seen to occur at the precipitate–matrix interface. The effect of voids and He bubbles on the fracture stress is much stronger. It was revealed that the plastic deformation was essentially suppressed. The reason for the suppression was attributed to the emission of the dislocations from voids/bubbles and their pile up.