Phase separation and crystallization in the bulk amorphous Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy

Phase separation and crystallization in the bulk metallic amorphous Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy was investigated by small angle neutron scattering (SANS), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). All samples were measured after selected isothermal annealing of the samples at 623K, or after linear heating treatments. After an incubation time of about 100min, the SANS data of isothermally annealed samples show interference peaks at about q=0.5nm(-1), indicating a periodic variation in the scattering length density with a wavelength of about 12.5nm. These scattering length inhomogenities turn out to be nanocrystals with sizes of 2...4nm and a number density of about 10(18) cm(-3). TEM images also indicate the presence of nanocrystals in the isothermally annealed samples. DSC results show an additional crystallization event and a second glass transition temperature. During the heat treatment, a decomposition of the alloy on a length scale of 12.5nm occurs. This decomposition process precedes the crystallization and is assumed to be responsible for the observed periodic arrangement of the nanocrystals. Samples that crystallized during linear heating experiments do not show SANS interference peaks. They exhibit larger crystallites with a broad size distribution due to a different crystallization behavior.