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

The substructure of martensite and the intervariant boundary structure in t he deformed 18R martensite in a Cu-Zn-Al shape memory alloy have been inves tigated in detail by a high resolution electron microscope (HREM). It is fo und that the deformation-produced dislocations, which mainly appear in the (0018) plane, extend into partial dislocations with a spacing of between fi ve and eight atomic layers. In addition to (0018)[010] slipping, dislocatio ns in the ((1) over bar 28) plane are also found. To accommodate strain, la ttice rotation takes place near the boundary plane to bring close packed pl anes of the related variants into parallelism, reducing the resistance for the boundary to move. The intervariant boundaries in the same plate group o r between different groups develop into stepped boundary structure due to d eformation. 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 reserv ed.