Structure of multi-grain spherical particles in an amorphous Ti50Ni25Cu25 melt-spun ribbon

Microstructural observations of crystalline particles created by controlled thermal treatments in an initially amorphous Ti50Ni25Cu25 melt-spun ribbon have been carried out by means of transmission electron microscopy (TEM). After annealing at temperatures close to the crystallization temperature during short times (10 min at 693 K), a low dispersion of micrometric particles embedded in the amorphous matrix is obtained. Their lattice structure is cubic (austenite) and many of them exhibit a single crystallographic orientation, although particles with several grains have also been observed. In the latter case, each grain grows radial and simultaneously from the center of the particle, producing a spherical crystalline area divided in several crystallographic grains. Most of them show rather planar interfaces between adjacent grains in TEM images and twinning relationships in selected area electron diffraction patterns (SAEDP). However, the directions of the twinning planes in the SAEDP do not match with the traces of the interfaces between the corresponding grains observed in the TEM images. The experimental results indicate that the growth of the particular grains does not occur independently, and suggest that additional topological conditions yield the interfaces different from the twinning planes.