Tensile Creep And Stress Relaxation Behaviour Of Cu-Zr Metallic Glass

The deformation behaviour of metallic glass is closely related to the relaxation behaviour which are both current research hotspots in amorphous materials science.Cu-Zr binary metallic glass system has become one of an ideal model material because of its simple chemical component and excellent mechanical properties.In this work,Cu₅₀Zr₅₀ and Cu₆₀Zr₄₀ binary metallic glasses ribbons have been systematically studied by uniaxial tensile creep at temperature close to the T_g?glass transition temperature?via DMA?Dynamic Mechanical Analyzer?.The T_g was measured by DSC?Differential Scanning Calorimeter?and DMA under same heating rate respectively.The creep apparent activation energies obtained from Arrhenius equation for Cu₅₀Zr₅₀ and Cu₆₀Zr₄₀ are 5.3 eV and6.2 eV respectively,it indicates that the tensile creep deformation in Cu-Zr metallic glass is related to the glass transition??-relaxation?behavior.Creep stress exponent decreases to¹ with the increasing temperature,this result shows Cu₅₀Zr₅₀ and Cu₆₀Zr₄₀ metallic glasses tend to be Newtonian viscous flow when it approaches to glass transition stage.To futher investiagate the temperature dependence on activation energy,we calculated the activation energy of creep?Q_c?over a broad temperature range from room temperature?RT?to glass transition temperature?T_g?for Cu₅₀Zr₅₀ metallic glass.It is found that the activation energy spectra in different stress show similar tendencies,dramatically low at low temperatures,rise at sub-T_g temperatures and peaking around T_g.To further investigate the correlation between creep and relaxation behavior in Cu-Zr metallic glass,dynamic mechanical measurements were conducted to acquire loss modulus-temperatures curves with varying frequency in tensile model.The activation energy for secondary???relaxation,E_?,was measured to be?129±6.5?kJ/mol,which corresponds to the transitional stage energy value in Q_c.Besides,Cu₅₀Zr₅₀ metallic glass ribbons have been studied by uniaxial tensile stress relaxation at temperature close to the T_g.The temperature,initial strain and cycle index dependences on stress relaxation were systematically discussed by KWW model.It was found that relaxation exponent?decreases with increased temperature.When initial strain and cycle index increase,relaxation exponent?decreases,initial stress and relaxation time increase,the results show that the content of flow units grow in number with complicated structures.