Thermodynamics and Kinetics of Deeply Supercooled Multicomponent Metallic Glass Forming Melts

本文的目的是研究过冷大块金属玻璃形成液体的热力学和动力学，以及玻璃化转变和抗结晶的热稳定性。它关注的问题是，为什么这些液体比以前的金属玻璃形成物更优越。Zr-Ti-Cu-Ni-Be合金具有高粘度，熔合热小，过冷液体和结晶混合物的吉布斯自由能差小。这表明，至少这种合金群是一种密度相当大的液体，自由体积很小。在拟议的研究中，选择不同的合金组将被检查，关于他们的动力学，热力学和结晶行为。将研究三组合金。一类是不含铍的早期过渡金属（ETM）基合金，其中ETM（TM）可以作为刚性骨架。第二组包括大块金属玻璃形成含Pd-Cu-Ni-P型的类金属液体，最后一组是基于简单金属，如Mg和Al。研究的目标是测量过冷液体的粘度作为温度，合金成分和剪切速率的函数，比热容，用熔合热和结晶热来确定合金的热力学函数，用粘度和焓弛豫实验来探测玻璃化转变的动力学，以及玻璃化转变温度对加热速率的依赖。此外，还研究了不同过冷度下的结晶动力学和微观结构。将使用和开发各种模型来分析粘度的结果。根据实验数据计算了热力学函数作为温度的函数，并利用Adam Gibbs理论将熵曲线的函数形式与粘度进行了比较。成核和生长模拟将应用于动力学和微观结构数据，测量的粘度和热力学驱动力被纳入这些计算。教育推广包括向本科生和当地高中生展示该计划的各个实验方面。大块金属玻璃具有高强度、大弹性应变极限、耐腐蚀和可成形性等特点，是一种令人兴奋的新型结构材料。此外，这些合金抗结晶的高热稳定性使得研究从熔点到玻璃化转变的过冷金属液体成为可能。在过去的实验中，这个区域还没有被随机封闭包装的液体所接近。所提出的工作将在复杂合金系统的结晶和玻璃成形性领域具有重要意义，这可以有技术基础，特别是在大块金属玻璃的加工方面。

The objective of this proposal is to study the thermodynamics and kinetics of supercooled bulk metallic glass forming liquids in conjunction with the glass transition as well as the thermal stability against crystallization. It focuses on the question why these liquids are superior glass formers compared to previous metallic glass formers. Together with the high viscosity, the Zr-Ti-Cu-Ni-Be alloys show small heats of fusion and a small Gibbs free energy difference between supercooled liquid and crystalline mixture. This indicates that at least this alloy group is a rather dense liquid with a small free volume. In the proposed research, a selection of different alloy groups will be examined with respect to their kinetics, thermodynamics and crystallization behavior. Three groups of alloys will be investigated. One group consists of early transition metal (ETM) based alloys that are free of Beryllium, in which the ETM(TM)s may serve as a rigid backbone. The second group includes bulk metallic glass forming metalloid containing liquids of the Pd-Cu-Ni-P type and the last group is based on simple metals such as Mg and Al. The goals of the study are to measure the viscosity of supercooled liquids as a function of temperature, alloy composition and shear rate, the specific heat capacities, heats of fusion and heats of crystallization to determine the thermodynamic functions of the alloys as well as the kinetics of the glass transition probed by viscosity and enthalpy relaxation experiments as well as the heating rate dependence of the glass transition temperature. In addition, the crystallization kinetics and microstructure for different degrees of undercooling will be investigated. Various models will be used and developed to analyze the results on viscosities. The thermodynamic functions are calculated as a function of temperature from the experimental data and the functional form of the entropy curve is compared with the viscosity via the Adam Gibbs theory. Nucleation and growth simulations will be applied to the kinetic and microstructural data and the measured viscosities and the thermodynamic driving forces are incorporated in these calculations. The educational outreach involves exposing undergraduate students as well as local high school seniors in various experimental aspects of the program. Bulk metallic glasses represent an exciting new class of structural materials, because of their properties like high strength, large elastic strain limit, corrosion resistance and formability. Furthermore, the high thermal stability of these alloys to resist crystallization allows investigation of supercooled metallic liquids from the melting point down to the glass transition. This region has not been experimentally accessible in the past for random closed packed liquids. The proposed work will have significance in the area of crystallization and glass formability of complex alloy systems, which can have technological underpinning, specifically in regard to the processing of bulk metallic glasses.