Nano-structures at martensite macrotwin interfaces in Ni65Al35Ni_{65}Al_{35}

The atomic configurations at macrotwin interfaces between microtwinned martensite plates in $Ni_{65}Al_{35}$ material are investigated using transmission electron microscopy. The observed structures are interpreted in view of possible formation mechanisms for these interfaces. A distinction is made between cases in which the microtwins, originating from mutually perpendicular \{110\} austenite planes, enclose a final angle larger or smaller than $90^{\circ}$. Two different configurations, a crossing and a step type are described. Depending on the actual case, tapering, bending and tip splitting of the smaller microtwin variants are observed. The most reproducible deformations occur in a region of approximately 5-10nm width around the interface while a variety of structural defects are observed further away from the interface. These structures and deformations are interpreted in terms of the coalescence of two separately nucleated microtwinned martensite plates and the need to accommodate remaining stresses