Experimental and Computational Thermodynamics of Some Ternary Transition Alloy Systems

点击翻译按钮获取中文摘要

TECHNICAL: Thermodynamic modeling of phase diagrams provides an opportunity to approach the phase equilibria aspects of alloy development in a more efficient manner than experimentally determining the phase equilibria in large numbers of alloys at many temperatures. The basic approach is to develop a thermodynamic description for the free energy of each phase as a function of composition and temperature and then to compute the minimum in free energy for a particular composition at a given temperature. In this way the phase diagram can be mapped in a matter of minutes or hours rather than the months involved with experimental methods of phase diagram determination. The accuracy of the computed diagram is dependent on the accuracy of the thermodynamic data used in the free energy descriptions of the phases. Such data on Al and Ni-base alloy systems are scarce or non-existent. For this reason it is common to utilize an existing phase diagram for the development of the thermodynamic models. Such models may not be unique and may not correctly reflect the underlying thermodynamics of the system. For reliable thermodynamic models it is essential to have some thermodynamic data on a system. In this project the PI will determine the heats of formation of a number of ternary Aluminum-Nickel-base alloy phases and some Rare earth B2 phases including the composition dependence for phases with substantial composition ranges. The heats of formation are determined using a custom-built high temperature reaction calorimeter with a typical accuracy of +/-1kJ/mole. In addition differential thermal analysis will be used to determine melting points and other phase transitions and differential scanning calorimetry will be used to determine heat capacity of selected alloys as a function of temperature. The DTA and DSC experiments will be performed in a SETARAM 1750 C calorimeter. The improved database will be used to compute several isothermal sections in each of the ternary alloy systems using Thermocalc. The data will also be used to validate various extrapolation models from the literature for the prediction of heats of formation of ternary compounds from binary data. NON-TECHNICAL: This project will maintain the only US based experimental thermodynamics group measuring alloy heats of formation and will provide training in this field to one graduate and two undergraduate students. A web server will be set up and maintained which provides the international community with a single source of recent experimental thermodynamic data from around the world. The data determined from the experiments will be used to develop an improved, self-consistent thermodynamic database for Aluminum-Nickel-base alloys in collaboration with Professor Bo Sundman, Division of Computational Thermodynamics, Royal Institute of Technology, Stockholm, Sweden and Dr. Evan Copland, NASA, Cleveland.