Orientation relationships and interfaces of the Fe-Zn intermetallic phases in galvannealed CMnSi-TRIP steels

Hot-dip galvannealed coatings of two Mn-Si TRIP steels have been characterized by transmission electron microscopy to study the crystallographic orientation relationships between the α-Fe and Γ1 phases, the Γ1 and Γ2 phases, as well as the Γ2 and δ phases. Both the α-Fe/Γ1 phases and the Γ1/Γ2 phases were found to exhibit a cube-on-cube orientation relationship. The orientation relationship at the Γ2/δ interface was identified to be 112¯0δ//[011]Γ2 and (0002) δ//111¯Γ2. The interfaces of Γ2/δ and Γ1/Γ2 are basically the close-packed plane of each phase. The nucleation of Γ2 phase between the δ and Γ1 phases was discussed by the heterogeneous nucleation theory based on the orientation relationships and the interfaces.