强脆转变是玻璃形成液体在从低温到高温升温过程中由强性液体转变为脆性液体的现象,反之从高温到低温冷却过程即为脆强转变.由于其意味着液体的结构发生了某种快速、非连续的变化,强脆转变现象成为异常动力学的典型代表.自1999年《Nature》杂志首次报道了水的强-脆转变现象之后,液体的强脆转变现象就作为凝聚态物理和材料科学领域中的前沿和热点问题被广泛关注.越来越多的研究表明,强脆转变现象在金属玻璃形成液体中普遍存在.为阐明金属玻璃强-脆转变现象对于深入理解玻璃转变本质、探讨液固遗传微观结构特征、揭示晶化过程相互竞争规律、提高玻璃形成能力、促进金属玻璃制备和处理工艺标准化等方面的重要意义,综合评述了强脆转变现象在金属玻璃形成液体中的普遍性、特殊性、定量表征、热力学表现以及结构起源等研究领域的最新进展,并指出了该领域今后的发展方向.%It has been observed that many glass-forming liquids are transformed from fragile to strong liquids in a supercooled region upon cooling. This is the so-called fragile-to-strong (F-S) transition. Since its discovery in water, the F-S transition, as a frontier problem, as well as a hot issue, in condensed matter physics and material science, has aroused the considerable interest of researchers. It has been generally accepted that the F-S transition might be a universal dynamic behavior of metallic glass-forming liquid (MGFL). Studying the F-S transition is important not only for better understanding the nature of glass transition, uncovering the microstructural inheritance during the liquid-solid transformation, clarifying the structural competition during crystallization, improving the stability of MGs, but also for promoting the standardization during the production and treatment technology of MGs. In this paper, the general and special features of the F-S transition for bulk and marginal MGFLs are studied and described in terms of a physical model. A characteristic parameter f is introduced to quantify the F-S transition. With two relaxation regimes, on the basis of Mauro-Yuanzheng-Ellison-Gupta-Allan model, we propose a generalized viscosity model for capturing the liquids with the F-S transition. Using this model, we calculate the F-S transition temperature for metallic glass. From the calculation results, the F-S transition might occur around (1.36 ± 0.03) Tg. By using the hyperquenching annealing-calorimetric approach, we find that the anomalous crystallization behavior occurs in both LaAlNi and CuZrAl glass ribbons. This phenomenon implies the existence of a thermodynamic F-S transition, which could be used as an alternative method of detecting the F-S transition in MGFLs. To date, the origin of the F-S transition is far from understanding. We find that the F-S transition in CuZr(Al) GFLs is attributed to the competition among the MRO clusters composed of different locally ordering configurations. By comparing the parameter f with the parameter r that characterizes the competition between the αand the slowβrelaxations in 19 MGFLs, we find that the slowβrelaxation plays a dominant role in the F-S transition and the extent of the F-S transition is mainly determined by the degree of the comparability in structure units between the α and the slow β relaxations. The existence of the liquid-liquid phase transition might also be the root of the F-S transition. The tendency of investigation of the F-S transition is also evaluated.
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