Parameter Selection Of Temperature Modulated Thermal Analysis Technology And Its Research On Enthalpy Relaxation Of Metallic Glasses

Amorphous materials are metastable materials with no periodicity in structure and non-equilibrium in energy,so relaxation behaviors is the most intrinsic feature of amorphous materials.After annealing at a proper temperature for an appropriate time,high energy hyperquenched glass obtained by a rapid cooling rate will occur a series of complex relaxation behaviors on the heat flow curve,including exothermic enthalpy relaxation and sub-T_g peak.However,compared with the theoretical explanation of enthalpy relaxation,the research of sub-T_g peak is still insufficient.The appearance of the sub-T_g peak is closely related to the glass transition,which is of great significance in the study of the glass transition and the relaxation dynamics mechanism.In this paper,conventional differential scanning calorimetry(DSC)and temperature modulated differential scanning calorimetry(TMDSC)are used to study the characteristic change of sub-T_g peak,the effect of glass transition and relaxation in the hyperquenched glass under different annealing conditions.TMDSC is a linear heat capacity measurement method based on heat flow.Two different time scales are introduced in the experiment at the same time.The choice of parameters determines whether the overlap phenomenon can be separated from the total modulation heat flow curve accurately,so it is necessary to explore the parameters.Firstly,TMDSC is used to give the modulated heat flow curves obtained under different modulation parameters in the amorphous materials of selenium,boron trioxide,Pd₄₀Ni₁₀Cu₃₀P₂₀and Au₄₉Ag_5.5Pd_2.3Cu_26.9Si_16.3 metallic glasses,and the optimal modulation parameters are given.Then,we performed DSC and TMDSC on Pd₄₀Ni₁₀Cu₃₀P₂₀and Au₄₉Ag_5.5Pd_2.3Cu_26.9Si_16.3 metallic glass ribbons under different annealing temperatures and different annealing times,a series of thermodynamic parameters were obtained,and the thermal stability of annealing process was analyzed.The influence of sub-T_gpeak on the onset temperature of dynamic glass transition under differernt conditions is discussed,and it was analyzed that the sub-T_g peak promotes the increase of the onset temperature of dynamic glass transition after it enters supercooled liquid,which ultimately leads to the improvement of the dynamic stability of the metallic glasses.At the same time,the evolution process of sub-T_g peak is a continuous evolution process from glass to supercooled liquid.Our results show that the evolution of the sub-T_g peak may be a localized dynamic process related to the glass transition,revealing the internal relationship between the evolution of the sub-T_g peak and the dynamic glass transition,which is a new inspiration for understanding the relaxation behavior and aging of metallic glass.