Tendency of primary crystal formation in ZrTiCuNiBe metallic bulk glasses

Bulk metallic glasses can be produced from the liquid melt at low cooling rates of <103 K/s. Although the bulk glasses appear to be fully amorphous when analyzed by X-ray diffraction (XRD), frequently small volume fractions of primary crystals are found. This problem is of various importance for the different bulk glass forming systems and even for glasses of the same family, but with different composition. For instance, the Zr41Ti14Cu12.5Ni10Be22.5-bulk glass is nearly free of crystals, whereas the thermally more stable Zr46.8Ti8.2Cu7.5Ni10Be27.5-bulk glass always contains a larger number of crystals, when produced under the same conditions. In the present work, the composition, structure and morphology of primary crystals in both ZrTiCuNiBe-bulk glasses are analyzed. These crystalline phases are compared with the equilibrium phases, which crystallize during very slow cooling of the liquid melt. The tendency for primary crystal formation is discussed in terms of constitutional arguments using a description of the ZrTiCuNiBe alloy by a quasi-ternary (Zr, Ti)-(Cu, Ni)-Be system.