Real-time detection of metastable phases in Zr-based bulk glasses during fast heating in a synchrotron beam

We have studied in situ crystallization from the glassy state and solidification from the liquid state in Zr-based bulk glass-forming alloy. The experiments were performed with a high intensity, high-energy monochromatic synchrotron beam. Samples of amorphous Zr₅₅Cu₂₀Al₁₀Ni₁₀Pd₅ alloy with rectangular section and 2 mm thickness, sealed under vacuum in specially designed quartz tubes were studied. Diffraction in transmission was used to minimize surface crystallization effects. The choice of the sample thickness and the monochromatic beam energy allow an acquisition time of 2 s per full pattern. The heating rate was around 20 K/s nearly 20 times greater than that usually used in DSC calorimetry and close to those of cooling rates for glass formation. In Zr₅₅Cu₃₀Al₁₀Ni₅, crystallization occurs via initial nucleation of a metastable phase that remains only a few seconds before transformation to the equilibrium phase, tetragonal Zr₂Cu. The increase of Zr content to 69% increases the stability of the metastable phase, which remains until melting. It was found that the Pd addition to the quaternary alloy with Zr 55 at.% also makes the metastable phase stable up to a temperature near melting. We have also found that, contrary to the Zr addition, the Pd addition eliminates the formation of bcc or hexagonal solid solution phase at high temperatures.