Factors affecting stacking fault contrast in transmission electron microscopy Comparisons with image simulations

Abstract

Factors that affect stacking fault contrast in transmission electron microscopy have been studied with the aid of a many-beam program for calculating computer simulated images. In the first part of this work, simulated images were used to verify the standard methods that are generally used to identify the intrinsic/extrinsic nature of stacking faults. These methods were found to be valid when the fault had an average inclination in the thin foil, but geometrical exceptions to these rules were also observed. A geometric parameter that accounts for the orientation of the fault with respect to the diffraction vector (g) and the beam direction (B) has been proposed. In the second part, the effect of the strain field of the bounding dislocations on stacking fault contrast has been studied, and it was found that these effects can be significant when the dissociation distance is small and the Burgers vectors of the bounding dislocations are large. A comparison of experimental and simulated images of stacking fault dipoles in TiAl are presented in order to underscore the influence that the bounding dislocations can have on the stacking fault contrast. The advantages to be gained by comparing experimental observations with simulated images have been illustrated.