HIGH-RESOLUTION ELECTRON-MICROSCOPY OF THE SIGMA=5 [001] (310) GRAIN-BOUNDARY IN NIAL

The structure of a highly oriented NiAl Sigma=5 [001](310) grain bound ary has been imaged by high-resolution electron microscopy and analyse d by multislice image calculations. This grain boundary exhibits an as ymmetry produced by a rigid body displacement of approximately 1/2d(1( 3) over bar0$) along the grain boundary, but does not show any measura ble expansion of the grain boundary. The match between the simulated a nd experimental images of this grain boundary is improved by changing the stoichiometry of the boundary, which can be accomplished by adding antisite defects and vacancies. The final model structure incorporate s 50% constitutional vacancies on the nickel sites adjacent to the bou ndary plane and a replacement of the aluminium sites adjacent to the b oundary plane with 50% nickel antisite defects and 50% vacancies.