Investigations of three- dimensional geometry of annealing twins in FCC metals

Three-dimensional studies were conducted of the geometry of twin grains in NiMn2 alloy, Ni--1.8Mn--0.4Co--o.2Fe--0.1Si--0.1Cu--0.05Mg. The twins are shown to have a complicated three-dimensional geometry and can be viewed as aggregates of plate-like blocks of varying size and arrangement. Planar intersections of such aggregates result in different "types" of twin geometry, which in reality might have the same topological characteristics. The classification of twin grains based on observations made on a two-dimensional cross-section thus does not have much physical significance. 20 ref.--D.O.N.