Correlating dynamic relaxation and viscoelasticity in metallic glasses

Relaxation dynamics,essential for the structural evolution of non-equilibrium systems like glassy materials,remain enigmatic.Here,we explore relaxation dynamics and viscoelastic properties in three types of metallic glasses with distinctβrelaxation behavior.In systems with significantβrelaxation,stress relaxation and creep experiments reveal a transition from two-step to one-step relaxation with rising temperature.However,such a phenomenon is absent in systems with weakerβrelaxation.We model the two-step relaxation process using a double Kohlrausch-Williams-Watts equation,and the obtained relaxation times elegantly adhere to the Arrhenius relationship.By combining fitted activation energies with theoretical analysis,we conclusively attribute these relaxation processes toβrelaxation andαrelaxation,respectively.Finally,we analyze the relaxation time spectra of two processes and establish a comprehensive picture linking dynamic relaxation with viscoelasticity.Our study provides new strategies for probing the complex relaxation behaviors of glasses from the perspective of viscoelasticity.

The anelastic origin of mechanical cycling induced rejuvenation in the metallic glass

Mechanical cycling is one of the effective methods to rejuvenate metallic glasses(MGs)and improve their mechanical properties.The anelastic origin of the rejuvenation by mechanical cycling in a La_(30)Ce_(30)Ni_(10)Al_(20)Co_(10) MG was investigated via differential scanning calorimetry(DSC)and dynamic mechanical analysis(DMA).We demonstrate that mechanical cycling promotes the activation of flow defects with short relaxation times,leading to anelastic strains and therefore considerable energy storage,which manifests itself as larger relaxation enthalpy on the DSC curves of MGs.However,the MGs release the excess relaxation enthalpy caused by anelastic strain with time,thus suppressing atomic mobility and elevating β relaxation activation energies.The strategy of mechanical cycling at small strains,as demonstrated in the current work,can expand the energy states of MGs over a wide range of relaxation enthalpies.

Dynamic mechanical relaxation and thermal creep of high-entropy La_(30)Ce_(30)Ni_(10)Al_(20)Co_(10)bulk metallic glass

Dynamic mechanical relaxation is a fundamental tool to understand the mechanical and physical properties of viscoelastic materials like glasses.Mechanical spectroscopy shows that the high-entropy bulk metallic glass(La_(30)Ce_(30)Ni_(10)Al_(20)Co_(10))exhibits a distinctβ-relaxation feature.In the present research,dynamic mechanical analysis and thermal creep were performed using this bulk metallic glass material at a temperature domain around theβrelaxation.The components of total strain,including ideal elastic strain,anelastic strain,and viscous-plastic strain,were analyzed based on the model of shear transformation zones(STZs).The stochastic activation of STZ contributes to the anelastic strain.When the temperature or external stress is high enough or the timescale is long enough,the interaction between STZs induces viscous-plastic strain.When all the spectrum of STZs is activated,the quasi-steady-state creep is achieved.

Aging and rejuvenation during high-temperature deformation in a metallic glass

High-temperature deformation has been demonstrated as an effective measure to rejuvenate and optimize the mechanical properties of metallic glasses(MGs).Clarifying the competition between aging and rejuvenation during high-temperature deformation is helpful in rejuvenating MGs accurately.Signatures of aging and rejuvenation in a La_(30)Ce_(30)Ni_(10)Al_(20)Co_(10)MG were investigated via high-temperature deformation and mechanical relaxation.The coupling of thermal history,aging,and mechanical disordering determines the transient deformation and the structural state of MGs.The stress overshoot and anelastic deformation induce structural rejuvenation,increasing the concentration of defects and erasing thermal history.Therefore,the eventually steady-state condition is dependent on ambient temperature and strain rate instead of the initial structure.Furthermore,the one-to-one relationship between defect concentration and strain rate clarifies the structural nature of rejuvenation in amorphous materials.Such a relationship also contributes toward a comprehensive understanding of the structural rejuvenation behavior in amorphous materials.

Effect of physical aging and cyclic loading on power-law creep of high-entropy metallic glass

The power-law relationship between creep rate decay and time is one of the intrinsic characteristics of metallic glasses.In the current work,a La_(30)Ce_(30)Ni_(10)Al_(20)Co_(10) high-entropy metallic glass was selected as the model alloy to test the influences of physical aging and cyclic loading on the power-law creep mechanism,which was probed by the dynamic mechanical analysis in terms of the stochastic activation,and contiguous interplay and permeation of shear transformation zones.It is demonstrated that a notable discrepancy appears between thermal treatment and mechanical treatment on the power-law creep mechanism of this high-entropy metallic glass.On the one hand,physical aging below the glass transition temperature introduces the annihilation of potential shear transformation zones which contribute to creep.On the other hand,cyclic loading can tailor the“forward”jump operations competing with the“backward”ones of shear transformation zones by controlling the interval time(recovery time).The current research offers a new pathway towards understanding the creep mechanism of high-entropy metallic glasses.