Microstructural studies of crystallization of a Zr-based bulk metallic glass

The evolution of the microstructure of a Zr 52.5Ti 5Cu 17.9Ni 14.6Al 10 alloy during isothermal annealing near the glass transition temperature was studied by transmission electron microscopy (TEM), small-angle neutron scattering (SANS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). In situ SANS experiments show that an interference maximum develops with isothermal annealing, which is attributed to decomposition in the undercooled liquid state. In agreement with these results, TEM observations show the formation of structural inhomogeneities in the glassy alloy in the early stages of annealing, which are correlated with the partially crystalline microstructure in the later stages. The TEM and XRD data show that finally two nanocrystalline phases form after long-term annealing as a result of the decomposition process in the early stages. Direct evidence for decomposition was obtained using Z-contrast imaging technique that showed a systematic variation of the Zr concentration between the two nanocrystalline phases.