کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
1485124 | 1510533 | 2007 | 16 صفحه PDF | دانلود رایگان |
The change in enthalpy on structural relaxation of two bulk metal–alloy glasses, Mg65Cu25Tb10 and Zr46.75Ti8.25Cu7.5Ni10Be27.5 has been investigated by differential scanning calorimetry (DSC) using an anneal-and-scan procedure. Two aspects of this relaxation have been investigated: (i) a monotonic decrease in the enthalpy with time, (ii) an increase in enthalpy with time and then a decrease, or the so-called ‘memory effect’. The non-exponential, non-linear model with a structure-independent parameter β fits the Cp scans, but yields a lower β value than an equally good fit to the isothermal enthalpy decrease without non-linearity. The memory effect is more pronounced in Zr46.75Ti8.25Cu7.5Ni10Be27.5 glass for which β is smaller. Despite the chemical and topological short-range order in their structures and no rotational diffusion, these glasses mimic the molecular, polymeric and network structure glasses. It is suggested that a reliable analysis of the memory effect data requires including a contribution from localized motions and avoiding the use of a time–temperature superposition. Even if this is done, molecular interpretation of the effect would depend upon whether a non-exponential relaxation is seen as a multiplicity of relaxation modes each with its own time and hence Tf, or another process that yields a characteristic overall time and Tf.
Journal: Journal of Non-Crystalline Solids - Volume 353, Issues 41–43, 1 November 2007, Pages 3796–3811