Twinned b.c.c. spherical particles in a partially crystallized Ti50Ni25Cu25 melt-spun ribbon

Some micrometric spherical particles containing several b.c.c. grains are obtained from an initially amorphous Ti50Ni25Cu25 melt-spun ribbon after a controlled thermal treatment. The microstructure and crystallography of these crystalline particles have been investigated by TEM, showing that each of the grains grows to the same distance from the center of the particle, keeping the isotropic growth of the entire system. The number of grains in each particle is variable, but self-accommodating arrangements have always been found. Most of the grains show {112}B2 (sometimes {114}B2) planes unchanged when moving to an adjacent grain, as typical twin crystals. However, the interfaces between adjacent grains usually do not match with these invariant planes. The morphology and self-accommodating arrangements found in these multi-grain particles are unusual for b.c.c. structures, but resemble in some way the case of multiple twinned particles present in other materials, as the five-fold twinned structures in f.c.c. systems.