3 - Dimensional reconstruction of annealing twins shape in FCC metals by serial sectioning

Reconstruction of the three-dimensional shapes of annealing twins in metals by serial section is discussed. In the investigated alloy Ni--2Mn, the twins can be divided into two populations: lamellar twins LT and corner twins CT. The first population contains approx 60% of the investigated twins. Boundary contours of a LT and its different views are presented. The shape of LTs is characterized by the existence of two parallel planes of coherent grain boundaries and highly geometrically irregular non-coherent twin and grain boundaries. During 2-D observations, LTs are frequently seen as island grains. The population of CTs contains twins of a shape that can be approximated by tetrahedrons. These twins are usually revealed on cross-sections in the form of triangles. Both types of twins occasionally show a step-like structure. Studies of the LTs localization proved that the twins frequently have one of the edges common with the grain. The twins usually end in the grain interior, but frequently they extend through the whole grain. It has also been observed that two or more twins in one grain can form complicated geometrical patterns defying simple analysis.