In situ high-energy x-ray diffraction observation of structural evolution in a Ti-based bulk metallic glass upon heating

The structural evolution of the Ti₄₀Zr₁₀Cu₃₄Pd₁₄Sn₂ bulk metallic glass (BMG) upon was investigated by means of in situ high-energy x-ray diffraction. The position, width, and intensity of the first peak in diffraction patterns are fitted through Voigt function below 800 K. All the peak position, width, and intensity values show a nearly linear increase with the increasing temperature to the onset temperature of structural relaxation, T_r = 510 K. However, these values start to deviate from the linear behavior between T_r and T_g (the glass transition temperature). The changes in free volume and the coefficient of volume thermal expansion prove that the aforementioned phenomenon is closely related to the structural relaxation releasing excess free volume arrested during rapid quenching of the BMG. Above 800 K, three crystallization events are detected and the first exothermic event is due to the formation of metastable nanocrystals.