The generation and application of metallurgical thermodynamic data
The power of thermodynamics in the calculation of complex chemical and metallurgical equilibria of importance to industry has, over the last 15 years, been considerably enhanced by the availability of computers. It has resulted in the storage of data in databanks, the use of physical but complex models to represent thermodynamic data, the vast effort spent in the generation of critically assessed data and the development of sophisticated software for their application in equilibrium calculations. This thesis is concerned with the generation and application of metallurgical thermodynamic data in which the computer plays a central and essential role. A very wide range of topics have been covered from the generation of data by experiment and critical assessment through to the application of these data in calculations of importance to industry. Particular emphasis is placed on the need for reliable models and expressions which can represent the molar Gibbs energy as a function of temperature and composition. In addition a new computer program is described and used for the automatic calculation of phase diagrams for binary systems. Measurements of the enthalpies of formation of alloys in the Fe-Ti system are reported. All data for this system have been critically assessed to provide a dataset consistent with the published phase diagram. Critically assessed data for a number of binary alloy systems have been combined in order to perform quantitative calculations in two types of steel system. Firstly data for the Cr-Fe-Ni-Si-Ti system have been used to provide information about the long term stability of alloys used in fast breeder nuclear reactors. Secondly very complex calculations involving nine elements have been made to predict the distribution of carbon and various impurities between competing phases in low alloy steels on the addition of Mischmetall. Finally a new model is developed to represent the thermodynamic data for sulphide liquids and is used in the critical assessment and calculation of data for the Cu-Fe-Ni-S system. The phase diagram and thermodynamic data calculated from the assessed data are in excellent agreement with those observed experimentally. The work reported in this thesis, whilst successful, has also indicated areas which will benefit from further study particularly the development of reliable data and models for pure elements, ordered solid phases and liquid phases for high affinity systems.