Crystallography of the Simple HCP/FCC System

The edge-to-edge matching model has been used to predict the orientation relationships (ORs) between crystals that have simple hexagonal-close-packed (HCP) and face-centered-cubic (FCC) structures. Using the critical values for the interatomic spacing misfit along the matching directions and the d- value mismatch between matching planes, a total of seven ORs have been predicted for the most common HCP/FCC metallic systems. However, the ORs that appear more frequently in a particular system depend on the type of matching directions and the interatomic spacing misfit along these directions together with the d- value mismatch between the matching planes. The latter two are related to the lattice parameters of both phases. For example, in the Al/Ag 2 Al system, three ORs have been predicted. One is , (0002) γ 0.027 deg from , which is consistent with the previously reported OR-1. The second is from . Due to the larger mismatch values, this OR is not expected to occur frequently and has not been found experimentally to date. Another predicted OR is from . This OR is very close to the reported OR-1. Details of zigzag atom row matching and the principles and process of refining an OR using the Δg conditions are also discussed.