Crystallization mechanism of Zr₅₅Cu₃₀Al₁₀Ni₅ metallic glass in an extended range of heating rates

The crystallization mechanisms of Zr₅₅Cu₃₀Al₁₀Ni₅ (Zr55) amorphous alloys from slow continuous heating to rapid laser heating are investigated. The multiphase nanocrystalline structures such as CuZr₂-type, NiZr₂-type and Al₂Zr₃-type phases with various compositions are observed at heating rates lower than 50 K/s, while the CuZr₂-type/ZrCu-type eutectic dendrites are produced at heating rates higher than 50 K/s. A numerical model is established to calculate the onset crystallization temperatures as a function of the heating rates. This model indicates that in addition to rapid dendritic growth from a certain number of quenched-in nuclei, the non-Arrhenius behavior of high diffusion coefficient in the supercooled liquid region contribute to the serious crystallization during rapid heating process. The activation energy of dendritic crystallization is obviously smaller than that of multiphase nanocrystallization, which is due to a much smaller scale of diffusion distance and larger atomic diffusivity during dendritic growth.