Thermodynamics and Kinetics of Deeply Supercooled Multicomponent Metallic Glass Forming Melts

该方案的目的是研究过冷块体金属玻璃形成液的热力学和动力学，同时结合玻璃化转变以及抗结晶的热稳定性。它关注的问题是，为什么这些液体是比以前的金属玻璃成型剂更好的玻璃成型剂。该合金具有较高的粘度，熔化热小，过冷液体与晶态混合物的Gibbs自由能差小。这表明，至少该合金基团是一种相当致密的液体，自由体积很小。在拟议的研究中，将从动力学、热力学和结晶行为方面考察不同合金组的选择。将对三组合金进行研究。一组由不含铍的早过渡金属基合金组成，其中早过渡金属S可能是一个刚性主干。第二组包括块状金属玻璃形成的含Pd-Cu-Ni-P类型的类金属液体，最后一组是以镁和铝等简单金属为基础的。该研究的目的是测量过冷液体的粘度随温度、合金成分和剪切速率、比热容、熔化热和结晶热的变化，以确定合金的热力学函数，以及通过粘度和热焓松弛实验来探索玻璃化转变的动力学，以及玻璃化转变温度对升温速度的依赖关系。此外，还将研究不同过冷度下的晶化动力学和微观结构。将使用和开发各种模型来分析关于粘度的结果。根据实验数据计算了热力学函数作为温度的函数，并通过Adam Gibbs理论比较了熵曲线的函数形式和粘度。形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将被纳入这些计算。教育外展包括让本科生和当地高中生了解该计划的各个实验方面。块体金属玻璃由于具有高强度、大弹性应变极限、耐腐蚀性和可成形性等特性，代表着一类令人兴奋的新型结构材料。此外，这些合金具有抗结晶的高热稳定性，因此可以研究从熔点到玻璃化转变的过冷金属液体。过去，对于随机封闭的堆积液体，这一区域在实验上是不能到达的。拟议的工作将在复杂合金系统的晶化和玻璃可成形性领域具有重要意义，这一领域可以有技术支持，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.