Precipitate assemblies formed on dislocation loops in aluminium-silver   alloys
  A detailed study of the precipitation of the \gamma' (AlAg2) phase in undeformed aluminium-silver alloys has been conducted. Several previously unreported features were observed, including the formation of discrete three-dimensional assemblies comprised of 5-7 precipitates on faulted dislocation loops. The precipitates assemblies adopted a morphology approximating a tetrahedral bipyramidal assembly. The bounding defect of the stacking fault was found to control both the nucleation of additional precipitates which was responsible for the formation of the assembly structure and also the growth characteristics of individual precipitates with these assemblies. 
Julian M. Rosalie, Laure Bourgeois and Barrington C. Muddle
cond-mat.mtrl-sci