Crystallization of Zr-based bulk metallic glasses during fast heating in a synchrotron beam

Direct real time observation of nucleation and crystallization in Zr-based bulk metallic glasses using high intensity high energy monochromatic synchrotron beam in transmission has been extended from the initial Zr₅₅Cu₃₀Al₁₀Ni₅ to alloys containing either titanium or a higher Zr content. Previously, it was established that crystallization of the amorphous phase occurs via initial nucleation and growth of metastable phases that transform to equilibrium tetragonal Zr₂Cu before melting. However, no trace of nucleation of the metastable phase was obtained during cooling of the liquid alloy from above liquidus temperature T₁ and Zr₂Cu forms directly from the liquid. The metastable crystalline nanostructure obtained during rapid heating was found to depend sensitively on the alloy composition. Ti addition suppresses the previously detected metastable state and leads to a new phase with structure close to that of tetragonal Zr₂Ni phase but with a highly stressed nanostructure. On the other hand, increasing the Zr content to nearly 70 at.% allows easy preparation of the metastable state during heating.