Heterogeneous Gd-Hf-Co-Al metallic glasses by liquid-liquid phase separation

The unique microstructures of phase separated metallic glasses can lead to enhanced properties of materials with its heterogeneity. Phase separated metallic glasses were prepared in Gd-Hf-Co-Al system by rapid quenching of the melt. The compositions were chosen by the combination of Gd-Co-Al and Hf-Co-Al alloys showing high glass forming ability. Strong positive enthalpy of mixing (ΔHmix)between the principal elements Gd and Hf leads to a heterogeneous microstructure of Gd-Hf-Co-Al glassy alloys consisting of two amorphous phases Gd-enriched and Hf-enriched. The length scale of spherical shaped heterogeneities ranges from a few nanometers to tens of micrometers. For clearly phase separated composition with nano-meter scale (100 nm) secondary phase separation is observed in each amorphous phase. Furthermore, thermal behaviour of Gd-Hf-Co-Al phase separated metallic glasses was investigated in order to analyze the composition dependence of glass transition temperature (Tg) and crystallization temperature (Tx), as well as phase sequences upon heating.