Microstructural features of phase transformation in a binary Pd-Si metallic glass

Glassy ribbons of Pd-Si alloys were prepared by a combination of melt spinning and flux treatment. The crystallization behaviour of a Pd81Si19 glassy alloy was studied through isothermal annealing at temperatures ranging lower than the glass-transition temperature Tg to around the onset of crystallization. The evolution of microstructures arising from isothermal annealing was investigated by X-ray diffraction (XRD) and (high-resolution) transmission electron microscopy ((HR)TEM). XRD spectra showed that, after the sample was annealed at a sub-Tg temperature, its first diffraction peak was split into two overlapping broad peaks. TEM analysis revealed the formation of a spherical, particle-like glassy phase embedded in the glassy matrix together with a finely connected network morphology within both. Combining these observations with compositional analysis suggested that phase separation had taken place during sub-Tg annealing. When the glassy alloy was annealed at temperatures higher than Tg, nanocrystalline structures, composed of Pd3Si and Pd phases plus a Pd9Si2 phase with a lamellar structure, was formed.