The atomic configurations at macro-twin interfaces between micro-twinned martensite plates in Ni65Al35 material were investigated by using transmission electron microscopy. The observed structures were interpreted in view of possible formation mechanisms for these interfaces. A distinction was made between cases in which the micro-twins, originating from mutually perpendicular {110} austenite planes, enclosed a final angle larger or smaller than 90°. Two different configurations, a crossing- and a step-type were described. Depending on the actual case, tapering, bending and tip-splitting of the smaller micro-twin variants were observed. The most reproducible deformations occurred in a region of approximately 5 to 10nm width around the interface while a variety of structural defects were observed further from the interface. These structures and deformations were interpreted in terms of the coalescence of 2 separately nucleated micro-twinned martensite plates and the need to accommodate any remaining stresses.

Nano-Structures at Martensite Macrotwin Interfaces in Ni65Al35. P.Boullay, D.Schryvers, J.M.Ball: Acta Materialia, 2003, 51[5], 1421-36