Study On Dynamic Mechanical Relaxation And Static Stress Relaxation Behavior Of High-Entropy Metallic Glasses

Relaxation is one of the most important and general properties of amorphous materials.It involves wide scales of time,frequency and temperature,and plays a decisive role in the properties and applications of amorphous materials.The mechanical relaxation behavior of amorphous materials is not only crucial for understanding the supercooled liquid,glass transition,and the stability of the materials,but also one of the core issues in the field of amorphous physics.Although high-entropy metallic glasses?HE-MGs?have developed rapidly in recent years,we know little about some critical issues such as their glass nature or thermal stability.Therefore,it is of cardinal significance to study the mechanical relaxation behavior of HE-MGs.In this paper,we systematically studied the dynamic mechanical relaxation of HE-MGs in supercooled liquid region and the static stress relaxation in glassy state,revealing the kinetic mechanism of the relaxation process and deepening the understanding of the mechanical relaxation process of HE-MGs.The main results are summarized as follows.The dynamic mechanical relaxation behavior of Ti₂₀Zr₂₀Hf₂₀Cu₂₀Ni₂₀,Ti20Zr20Cu20Ni20Be20,Ti20Zr20Hf20Cu20Be20 and Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 HE-MGs was investigated by the dynamic mechanical analysis?DMA?.The?relaxation process was obviously observed.The lower activation energy and fragility could be attributed to the crystallization process during?relaxation.The temperature and frequency dependence of dynamic mechanical properties were discussed by Kohlrausch-Williams-Watt?KWW?model and Quasi-Point Defects?QPD?model.The smaller value of?_KWW of Ti₂₀Zr₂₀Hf₂₀Cu₂₀Ni₂₀ indicates the wider relaxation time distribution and larger dynamic heterogeneity,while the small value of?indicates the lower atomic mobility during the relaxation.In combination with thermal stability studies,it was found that the relatively wide?relaxation time distribution in HE-MGs results from their high thermal stability,which leads to the slow atomic motion of the quenched samples.The dynamic mechanical analyzer was used to study the static stress relaxation process of HE-MGs.A decoupling of the relaxation from a single-step to a two-step?slow relaxation and fast relaxation?was found in the glass state below T_g.The slow relaxation process exhibits a stretched decay??<1?and a marked Arrhenius dependence on the temperature.The relaxation time decreases sharply with the increase of temperature,which may relate to the wider relaxation time distribution and the long-range atomic rearrangements at larger scales.The fast relaxation,with the appearance of compressed decay??>1?,may relate to the atomic scale internal stress dominated ballisticlike motion.The results obtained in our paper deepen our understanding of the mechanical relaxation behavior of HE-MGs,broaden the applicable range of relevant theoretical models,and provide new ideas for the performance optimization and applications of HE-MGs.