Abstract:The crystallography and morphology of precipitates in different systems were rationalized based on the optimum matching conditions. The interfaces that obey these conditions were conveniently identified in reciprocal space, in terms of three Dg’s parallelism rules. The theoretic basis of the O-lattice and CSL/DSC theory for these rules was provided briefly. Examples of small lattice misfit system (a Ti alloy), and large lattice misfit systems (Al and Mg alloys) were presented. The effect of lattice parameters on the orientation relationship and morphology was also discussed.

Key words: precipitation crystallography; interfacial orientation;  Dg parallelism rules; misfit strain