大块金属玻璃过冷液相区的形变及其对结构稳定性的影响

In recent years, particularly 90's in twenty century, significant progress has been made in the search for glass forming alloy system, which lead to the anufacture of the amorphous alloy in bulk form with an extremely low critical cooling rate. These bulk amorphous alloys typically exhibit distinct glass transition process, large supercooled liquid region and high thermal stability against crystallization and thus offer us a good opportunity to investigate not only the formation of metallic glass, structural evolution and glass transition but also the relationship between the microstructure and mechanical/physical properties.. In this research project, we have investigated the influence of element additions on the glass forming ability of multicomponent alloy system and microstructural characteristics, tructural relaxation, glass transition and thermal stability of bulk amorphous alloy. It is of significance to develop novel bulk glass-forming alloy system and further to understand the microstructure dependence of the metallic glass formation, tructural relaxation, glass transition, crystallization behavior and thermal stability of bulk amorphous alloy. The experimental data show that a limiting Be addition promotes the glass forming ability of ZrAlNiCu alloy system. The substitution of 12.5 at% Be for Zr induces the transition of Zr65Al10Ni10Cu15 amorphous alloy from an off-eutectic alloy into an eutectic one, and therefore enhances the reduced glass transition temperature Trg (Tg/Tm ) from 0.58 to 0.68, supercooled liquid region DTx from 105K to 142K. It has been verified that the enhancement of glass forming ability is associated with change of glass formation enthalpy from -26.55 KJ/mol to -30.61KJ/mol and the increase in the atomic size difference (Δa) by about 7% with adding Be. Analytic results in terms of quasi-point defect theory reveal that the ZrTiCuNiBe bulk amorphous alloy with 2%Fe has higher degree short range ordering and lower atomic ability and thus the extension of the average structural relaxation time and increase of viscosity. This is the key reason for the promotion of thermal stability for this alloy with Fe element addition. In order for the improvement of the applicability and relevant techniques for shaping bulk metallic glasses, large efforts have also been made on the study of the room temperature deformation and fracture mechanism as well as the flow behavior at high temperatures around the supercooled liquid region. Also included is the research on the influence of phase separation and primary ano-crystallization on the flow behavior of bulk amorphous alloy. The experimental results show that the tensile properties of bulk amorphous alloy are dependent on the strain rate at room temperature. While the failure of amorphous alloy is a process of nucleation of shear band and subsequent quick propagation for low strain rates, the fracture process of the materials could be considered to be an adiabatic shearing process at high tensile strain rates. It is found that homogeneous flow behavior of bulk amorphous alloy in supercooled liquid region depends on both temperature and strain rate. The transition state theory is applicable to explain the transition from Newtonian to non-Newtonian flow, yielding an activation energy of 413kJ/mol for viscous flow. The preliminary experimental results and analysis show that the flow behavior of the bulk ZrTiCuNiBe metallic glass at the temperature of 646K after phase separation and primary crystallizaion is mainly controlled by the viscous flow of remaining supercooled liquid, which follows a sinh relation similar to that of the initial homogeneous supercooled liquid. Concerning the influence of the deformation in suerpcooled liquid region on the microstructure, structural relaxation, glass transition and thermal stability of bulk metallic glass, it is noted that the glass transition emperature remains constant for the bulk amorphous alloy undergone the deformation at various temperatures in supercooled liquid range. However, as the magnitude of th

研究多组元大块金属玻璃过冷液相区的流变、超塑性形变特性；研究过冷液相区流变、超塑性形变与多组元大块金属玻璃微观结构特征的相互关系及其对金属玻璃热稳定性的影响。将有助于从原子尺度深入认识多组元非晶合金体系的结构特征和金属玻璃在过冷液相区的流变及超塑性形变机制；对金属玻璃材料成型加工、推进金属玻璃材料的实用化具有重要价值。.