Substructure and boundary structure of deformed 18R martensite in a Cu-Zn-Al alloy

The substructure of martensite and the intervariant boundary structure in the deformed 18R martensite in a Cu-Zn-Al shape memory alloy have been investigated in detail by a high resolution electron microscope (HREM). It is found that the deformation-produced dislocations, which mainly appear in the (0018) plane, extend into partial dislocations with a spacing of between five and eight atomic layers. In addition to (0018)[010] slipping, dislocations in the ((1) over bar 28) plane are also found. To accommodate strain, lattice rotation takes place near the boundary plane to bring close packed planes of the related variants into parallelism, reducing the resistance for the boundary to move. The intervariant boundaries in the same plate group or between different groups develop into stepped boundary structure due to deformation. These steps correspond to twinning dislocations whose movement results in the migration of the boundary perpendicular to itself. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.