Correlation Between Different Relaxations And Properties Of Metallic Glasses

As a frontier problem, as well as a hot issue, in condensed matter physics and material science, the relaxation behaviors in metallic glasses (MGs) have attracted considerable interests of researchers. The study of the correlation between different relaxation behaviors and properties of metallic glasses is of great importance not only for better understanding the nature of glass transition, uncovering the origin of the fragile-to-strong (F-S) transition and the microstructural inheritance during the liquid-solid transformation, but also for improving the plasticity of MGs, promoting the standardization during the production and treatment technology of MGs. Bear this in mind, in this project, we start with studying the evolution of different relaxation behaviors over temperature. Then, we focus on investigating how the competition between the α and the slow β relaxations is linked to the F-S transition in supercooled liquids (SLs) and the Poisson’s ratio of glassy solids. The innovative results have been achieved as follow:(1) By comparing the fragile-to-strong transition extent parameter f and the ratio r of the activation energies for the a and the slow β relaxations in different metallic glasses, it is the first time to discover the quantitative relationship between the extent of the F-S transition and the degree of the the competition between the α and the slow β relaxations. This relationship verifies that the extent of the F-S transition is mainly determined by the degree of the comparability in structure units between the αand the slow β relaxations. It has been also discovered that the F-S transition could be closely associated with the splitting of the slow β relaxation from the a relaxation when dropping to a critical temperature. This work provides new insight into the microscopic mechanism of the F-S transition.(2) By comparing the relaxation competition parameter r in SLs and the v values for both metallic and nonmetallic glasses, it has been found that there is a positive exponential-like correlation between v and r. Such a correlation implies that Poisson’s ratio v of glass is greatly determined by the comparability of the structure units involved in the a and the slow β relaxations in SL. The structural heterogeneity frozen-in during the SL-glass transition might be intimately associated with the glass plasticity. This work gives new insight into uncovering the microstructural inheritance during the liquid-solid transformation.(3) By combining calorimetric approach and viscosity measurement, the origin of different presentation of the slow β relaxation (excess wing, shoulder or peak) in La-based metallic glasses has been systematically studied. The experimental results show that, thermodynamically, the presentation of the slow β relaxation is greatly determined by the ratio between the relaxation temperature region of the slow P relaxation (Ta,c-Tonset) and the width of the SL region (Tx-Tg). The larger the Ta,C-Tonset is and the smaller the Tx-Tg is, the more obvious the slow β relaxation is. Beside, the slow β relaxation could be intimately associated with the structural changes during the liquid-liquid transition. The larger the difference between the structures before and after the liquid-liquid transition, the less obvious the slow β relaxation is.