The crystallography and interfacial structure of martensite in Cu-38.6%Zn has been studied by conventional TEM and reported in these proceedings. The parent phase is bcc and the martensite phase has a 9R close-packed structure with the stacking order “ABC/BCA/CAB/A” normal to the c axis. Here, the bcc-9R interfaces are studied by using high resolution electron microscopy. The coherency dislocation/step structure of enclosed second phase particles has been treated by Olson and Cohen. The most significant coherency dislocation/step in an interface is formed by the intersection of interface and the most close-packed lattice plane which is nearly parallel to the interface. The average habit plane of martensite in Cu-38.6%Zn determined from experiment and CRAB crystallographic theory is very close to (4 21 22)b which is 7.6° away from the most close-packed lattice plane (011)b. Therefore, the best crystallographic direction for high-resolution electron microscopy studies is [01]b where the habit plane and the (011)b are all edge-on. Unfortunately, in this beam direction there is only one set of lattice fringes from both parent and martensite phases which can be resolved and they provide little information about interfacial structure. As shown in Figure 1 the high resolution images are therefore taken along the [11]b lattice invariant line (anti-coherency dislocation line) direction where the interfacial boundary and the internal stacking faults of the martensite are near edge-on. Figure 1 (a) and (b) are in the same area but taken with different defocus. These images were taken using the Berkeley ARM operated at 800 kv.
From simple O(Bi,M)4entities to the large family of bismuth-based oxyphosphate compounds: use of high-resolution electron microscopy imaging to the deduction of new structure types
