Abstract
The possibility of additional strains in twinned Fe–Ni martensites (32.5%Ni) has been examined by analysing the traces of the twin interface planes, based on the two surface method with X-ray and optical microscopy techniques, besides electron microscopy of the fine details of twins. It has been verified from the two-surface analysis that the twin interface planes coincide with the (112) twinning plane within a few degrees, and therefore that large deviations between those planes, as detected in a previous electron microscopy, are apparent ones due to some bucklings of foil specimens. On the other hand, electron microscopy suggests the occurrence of slip on a plane including the [\bar1\bar11] twinning shear direction, revealing two kinds of twin traces even over a narrow region of the same martensite, and furthermore indicates the existence of planar faults or thin twins on the (1\bar2\bar1) or (\bar21\bar1)Tplane, accompanying streaks normal to the plane in diffraction patterns. From these results, it is suggested that the transformation twins in Fe–Ni martensites are subjected to additional strains by which the interface plane is not so much rotated (may be less than 3°) from the original (112) twinning plane.
