Structural relaxation of Ti-based bulk metallic glasses

The enthalpy relaxation behavior of Ti41.5Cu37.5Ni7.5Zr2.5Hf5Sn5Si1 bulk metallic glass (BMG) was investigated in this study. It is found that relaxation behavior follows the general characteristics for amorphous materials: the annealing time dependence of recovery enthalpy follows a stretched exponential function with the mean relaxation time obeying an Arrhenius law. In addition, the equilibrium recovery enthalpy !HT eq , mean relaxation time τ and stretching exponent β are annealing temperature dependent, and the higher the annealing temperature, the lower the values of eq T H Δ , τ and higher of β. The activation energy for enthalpy relaxation is calculated to be 3.06 eV, suggesting that the governing mechanism for the enthalpy relaxation process of this alloy is the rearrangement involving the collective hopping mechanism for the small and medium size atoms. Two parameters, βg and τg, representing the stretching exponent and the mean structural relaxation time at the calorimetric glass transition temperature, respectively, have been introduced to construct the correlation with glass forming ability and thermal stability. The high value of βg for Ti41.5Cu37.5Ni7.5Zr2.5Hf5Sn5Si1 BMG that is higher than 0.84 however lower than that of typical BMGs which approaches unity reveals its relatively good, however worse glass forming ability compared with typical BMGs; in addition, its high value of τg indicates its comparable good thermal stability with typical BMGs.