Effect of hydrofluoric acid treatment on the crystallisation behaviour of Zr-Ti-Cu-Al-Ni metallic glass

The surface of the metallic glass Zr59Ti3Cu20Al10Ni8 has been modified by hydrofluoric acid (HF) etching treatment. The devitrification and crystallisation process has been mainly studied by isothermal differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The nucleation-growth process is the mechanism of crystallisation; nevertheless the JMA-model is not applicable in every situation. Alternative methods are used to interpret the data. Results show the devitrification process is strongly affected by surface nucleation, which depends on the surface topology. Zr3Al2 is the first phase formed on the concave areas whereas the quasicrystalline and Zr2Ni-based phases appears in the flatter ones. Nevertheless, the presence of an oxide surface layer acts upon the surface nucleation and dwarfs the consequences of such topological differences. Moreover, the quasicrystalline formation appears also to be in competition with the parallel formation of ZrO2 due to thermal re-oxidation during the DSC experiments.