Reductions in stacking fault widths in fcc crystals: Semiempirical calculations

Recent molecular dynamics simulations of nanocrystals have illustrated the importance of stacking fault width for mechanical behavior and microstructure. Stacking fault (SF) width is a balance between elastic strain energy and the SF energy. While the latter is a material constant, the former strain energy may vary due to local internal stresses thereby effecting SF width. The presence and intensity of these stresses are functions of dislocation interactions in the crystal. Recent high resolution electron microscopy observations reveal a range of narrow SF widths within grains of different sizes including those less than 10 nm. To understand the reason for the presence of dislocations with small SF widths in metals, we first demonstrate theoretically and numerically with molecular statics simulation, the reductions in SF width due to dislocation stress screening. Different dislocation arrangements are examined including a dislocation wall. Second, the reduction in SF width in a thin film is examined via the introduction of free surfaces. These results reveal a wide variation of SF widths depending on structure and indicate that stress screening is an important mechanism for creating the narrow widths observed experimentally.